CA1282878C - Satellite communications system having multiple downlink beams powered by pooled transmitters - Google Patents

Satellite communications system having multiple downlink beams powered by pooled transmitters

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Publication number
CA1282878C
CA1282878C CA000543176A CA543176A CA1282878C CA 1282878 C CA1282878 C CA 1282878C CA 000543176 A CA000543176 A CA 000543176A CA 543176 A CA543176 A CA 543176A CA 1282878 C CA1282878 C CA 1282878C
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Canada
Prior art keywords
lines
satellite
signals
downlink
point
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CA000543176A
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French (fr)
Inventor
Harold A. Rosen
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DirecTV Group Inc
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Hughes Aircraft Co
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Classifications

    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01QANTENNAS, i.e. RADIO AERIALS
    • H01Q25/00Antennas or antenna systems providing at least two radiating patterns
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B7/00Radio transmission systems, i.e. using radiation field
    • H04B7/14Relay systems
    • H04B7/15Active relay systems
    • H04B7/204Multiple access
    • H04B7/2041Spot beam multiple access
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02DCLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00Reducing energy consumption in communication networks
    • Y02D30/70Reducing energy consumption in communication networks in wireless communication networks

Abstract

SATELLITE COMMUNICATIONS SYSTEM
HAVING MULTIPLE DOWNLINK BEAMS
POWERED BY POOLED TRANSMITTERS
ABSTRACT OF THE DISCLOSURE
A satellite communications system employs separate subsystems for providing broadcast and point-to-point two-way communications using the same assigned frequency band. The broadcast and point-to-point subsystems employ an integrated satellite antenna system which uses a common reflector (12). The point-to-point subsystem achieves increased communication capacity through the reuse of the assigned frequency band over multiple, contiguous zone (32, 34, 36 38) covering the area of the earth to be serviced. Small aperture terminals in the zones are serviced by a plurality of high gain downlink fan beams (29) steered in the east-west direction by frequency address. A special beam-forming network (98) provides in conjunction with an array antenna (20) the multiple zone frequency address function. The satellite (10) employs a filter interconnection matrix (90) for connecting earth terminals in different zones in a manner which permits multiple reuse of the entire band of assigned frequencies. A single pool of solid state transmitters allows rain disadvantaged users to be assigned higher than normal power at minimum cost. The intermodulation products of the transmitters are geographically dispersed.

Description

SATELLITE COMMUNICATIONS SYSTEM
HAVING MULTIPLE DOWNLINK BEAMS
POWERED BY POOLlED TRANSMITTERS

TECHNICAL FIELD

The present invention broadly relates to sateLlite eomT)unication systems~ especially of the type employing a s~tellite placed in geosynchronous orbit so as to fo~n a comnunication link between mQny sn~ll aperture terminals on the earth. More particularly, the invention involves a communications satellite having multiple transrnitters and the ability to simultaneously provide thousands of n~rrow, high gain antenna beams while drawing on the satellite's entire pool OI transmit$er power so that disQdvantaged users may be a^comnodated with higher power, vnthout reducing the satellite's overall channel capacity.

BACKGROUND ART

In a typical satellite system, either an areas~ride (e.g, n~tionwide) antenna beQm or narrow zone beams are ~nployed for canmlmications. In Ku band, the s~tellite colTmunication band most suitable for two-way service to very ~nall te~inals, the attenuation of the signals by rain is an ilr portant design eorlsideration. The rain attenuation is overcome on the downlink by using higher satellite trun~;mission power per channel than would be ne~essary ~or cleaP weather service, typically four t~nes as much. This approach to aeccmnodation of rain attenuation therefsre results in more expensi~e satellites having fewer ~vaila~le channels.

rypically, the geographic region covered by t~.e satellite is divided into zones with one downlink antenna beam being dedicated to each zone. When ~one downlink beams are employed) usuaUy each transmitter is associated with each zone and c~nnot be simultaneously used with any other zone. Although the use of zone beams is advantageous in that zcne beams have high antenna gain, these systerr~ do not sufficiently accomnodate disadvantaged dows~link users.
If a downlink user is located in an area experiencing heavy rainfall, in order to compensate for the rain attenuation, the uplink signal h~s to be made more powerful. Since each of the zone beams has a limited amount of power associated with it (iOe. the amount of power from its transmitter), the extra power needed to cornpensate ~or rain comes fran decreasing the amount OI power provided to the rest of the downlink users in that particular zone. Since the unattenuated users in the zone receive less power, the nunber of available channels in that particular ~one deereases because there is not enough power to supply all the users.

Conversely, systems employing one nationwide ~ntenna beam have a nationwide pool of power available to them because the nation is served by 8LI OI` the trar~nitter. To canpensate for rain attenuation, the uplink power can be increased without overtaxing the other users located throughout the nation. This is because the area over which heavy rain occurs at any instarlce, is ~naLI compared to the area of the entire nation. Hence the average penalty to the impaired users de~renses since their loss is spread out over a larger n~T~er o~
unimpnired users. Despite having a pool of power available, a nationwide bea n is not ideal for two-way ca~nuni~ations because Q wide antenna be~n rneans low anterma gain, ~nd for c~nnunication to very ~nall earth tenninals, a high gain antenna beam is highly desir~ble.

~J~

SUMMARY OF THE INVENTION

The s~tellite corrmunications system of the present invention combines the advan~ges of a narrow bean, i.e. a high downlink EIRP, w~th availability of a nationwide pool OI transrni~ter power, thus making it easy to overcome sign~l degr~dation due to fac~ors such as rain. The present system ITakes it feasible to overcome rain attenuation without reducing the satellite's overall channel c~pacity because the additional power required to c~npen~te for rain attenuation cornes from ~ large pool of transmitter power which serves the entire nation. Thus, the average penalty on unirnpaired users is rninin~ized because the reduction in available power is averaged out over thousands o~ users.

According to one aspect of the inventiorl) a meth~d is provided for con~municatively interconnecting any of a plurality terminal sites within ~n area on ~he earth using a comrnunications satellite. A
plurality of redio frequency uplink be~s, each c~rrying a receive signal, ~re transrnitted frorn uplink terminals sites in the area to a satellite, which is prefer~bly placed in geosynchronous orbit above the earth. The uplink bearrls are received at the satellite and the receive signals are converted to corresponding transmit signals destined to be transrnitted to downlink terminal sites in the area. All of the tr~nsrnit signals ~re eollectively Rrnplified using ~ plur~lity of arnplifiers at the satellite such that euch of the transmit si~n~ls is amplified collectively by all of the amplifiers. The sat011ite transmits to the area a plurality of downlink beams respectively covering portions of the area~ wherein each of the d~wnlink beams carrles one of the trarE;rr~it signals to be received by a downlink terminal site in a corresponding portion OI the ~reQ. The power of one or snore of the downlink be~ns is increased in order to overcoms the attenuating effects of rain by inCFeaSing the power of the uplink be~n carrying the corresponding re¢eive signal.

According to another aspect of the inYention~ an apparatus is provided for comn~nicatively interconnecting any of a plurality oî terrninal sites within an area on the earth. ~he apparatus includes a satellite preferably positioned in a geosynchronous ear-th orbit. The satellite carries means for respectively receiving from uplink terminal site~ in the area a plurality of uplink radio frequency beams s each carrying a rec~ive signal. Means carried by the satellite are provided for converting khe receive signals into transmit signals, each of which includes a plurality of corresponding subsignals destined to be received at downlink terminals sites in the area, where the conversion is performed by changing the frequencies o~ the receive signals. A plurality of ampli~iers carried by the satellite collectively amplify all of the transmit signals such that each of the transmit signals is amplified by all oP the amplifiers. The sat~llite includes beam-forming means for plurality of downlink radio frequency beams each carrying one of the transmit subsignals destined to be received by one of the downlink terminal sites and covering only a portion of the area. Means are also provided on the satellite for rPspectively transmitting the downlink beams to corresponding portions of the area. Each of the transmit subsignals is a fre~uency division multiplex signal, and each of the downlink beams is frequency addressable. The transmitting meanæ includes an array of antenna elements Eor radiating electromagnetic energy, wherein the antenna array has a plurality of input transmit array element~ respectively coupled with the amplifiers of the transmit signals. The power of the receive signals in each of the uplink beams is essentially proportional to the power of the corresponding subsignal in each o~ the downlink beams~
It is an object of one aspect of the present invention to provide a satellite communications system providing a multiplicity o~ narrow~ high-gain downlink beam collectively powered by a pool of individual transmitters in order to overcome localized signal degradation to rain or the like without reducing the channel capacity of the system.
An object of another aspect of the present invention is to provide a system as described above which allows accommodation o~ disadvantaged downlinX
u~er sites without the need for substantially reducing the power of downlink signals transmitted to non-disadvantaged downlink usersO
An object of a further aspect o the present invention is to provide a system as described above having means for gorming downlink transmit signals in a manner which allows all of the trans~it signals to be amplified by a set of pooled amplifiers in a manner such that each transmit signal is amplified by all of the amplifiers.
These, and further objects and advantages of the present invention, will be made clear or will become apparent during the course of the following description of a preferred embodiment of the present invention~
Various aspects of the invention are as follows:
Apparatus for communicatively interconnecting any of a plurality of terminal sites within an area on the earth, comprising:
a satellite posi~ioned above the earth;
means carried by qaid satellite for respectively receiving from uplink terminal sites in said area a plurality of uplink radio frequency beams each carrying a receive signal;
means carried by sai~ satellite for converting said receive signals into transmit signals each including a plurality of corresponding subsignals destined to be raceived at downlink terminal sites : in said area by changing the frequencies of said receive signals;
a plurality of amplifiers carried by said satellite for collec~ively amplifying all of said 5a transmit signals such that each o~ said transmit signals is amplified by all of said amplifiers; and means carried by said satellite for forming a plurality of downlink radio fre~lency beams each carrying one of said transmit subsignals destined to be received by one of said downlink terminal sites and primarily covering only a portion of ~aid area, said beam-forming means including -(1~ a first plurality o~ lines for respectively carrying said transmit signals, and ~2~ a second plurality of spaced apart lines intersecting said first plurality of linss at crossoYer points and extending radially from a reference point so as to diverge from each other, each of said second ~lurality of lines being coupled with each of said first plurality of lines at said ~rossover points such that a portion of the energy of each of the transmit signals carried by each of the first plurality of lines is transferred to each of said ~econd plurality of lines, aach of said second plurality of lines having an output for outputting all of said transmit signal~, each of said outputs being associated with and coupled to one of said amplifiers such that ea~h of said amplifiers amplifies all the transmit signals from an associated one of said amplifiers; and means carriPd by said satellite for respectively transmitting said downlink beams to corresponding portions of said area.
Apparatus for communicatively interconnecting any of a plurality of terminal sites within an area on the earth, compri~ing:
~ satellite positioned above the earth;
means carried by said satellite for respectively receiving ~rom uplink terminal sites 5~
in said area a plurali y of uplin~ radio frequency beams each carrying a receive signal;
means carried by said satellite for converting said receive signals into transmit signals each S including a plurality of corresponding subsignals destined to be received at downlink terminal sites in said ar~a by changing the frequencies of said receive signals;
a plurality of ampli~iers carried by said lo satellite ~or collectively amplifying all o~ said transmit signals such that each of said transmit signals is amplified by all of ~aid amplifiers; and means carried by said satellite ~or forming a plurality of downlink radio frequency beams each carrying one of said transmit subsignals destinPd to be received by one of said downlink terminal SitQs and primarily covering only a portion o~ said area, said beam-fo~ming means including -(1) a first pluxality of lines for respectively carrying said transmit signals, and (2) a second plurality o~ spaced apart lines intersecting said first plurality of lines at crossover points and extending radially from a reference point so as to divexge ~rom each other~ each of said second plurality of lines being coupled with each of said first plurality of lines at said crossover points ; such th~t a portion of the energy of each of the transmit signals carried by each of the ~irst plurality of lines is transferred to each of said second plurality of lines, each of said second plurality of lines having an output for outputting all of said transmit signals, each of said outputs b~ing associated with and coupled to one of said amplifiers such that each of said amplifiers amplifies all the transmit signals from an associated 3L7d 82~ ~
5c one of said amplifiers, said first plurality of lines extending circumferentially about a reference point and being radially spaced relative to said re~erence point such that the distance between adjacent crossover points increases with increasing radial distance of the crossover points from said reference point; and means carried by said satellite for respectively transmitting said downlink beams to corresponding portions o~ said area.
BRIEF D~sc~IpTIoN OF ~ DRAWIN~S
In the 2ccompanying drawings:
Figure 1 is a perspective view o~ a communications satellite, showing the antenna subsystems, Figure 2 is a top plan view of the antenna subsystem6 shown in Figure l;
Figllre 3 is a sectional view taken along the line 3-3 in Figure 2;
~igure 4 is a sectional view taken along the line 4-4 in Figure 2;
Figure 5 is a view of the United States and depicts multiple, csntiguous receive 20nes covered by the satellite of the presant invention, the primary areas of coverage being indi~ated in cross-hatching and the areas of contention being indicated by a dimpled patt~rn;

7~

Figure 6 is a block diagram of the comnunic~tion electronics for the comnunications satellite;

Figure 7 is a schematic diQgram of ~ coupling net~qork which interconnects the point-to-point receive feed horns with the inputs to the comnunic~tions electronics shown in Figure 6;

Figure 8 is a reference table of the interconnect channels elr~loyed to connect the receive and transmit zones for the point-to-point system;

Figure 9 is a diagrarnnatic view of the United States depicting multiple contiguous transmit zones coYered by the satellite and the geographic distribution of the interconnec$ed channels for each zone~
across the United States;

Figure 9A is a graph showing the variation in ~Qin of the trRnsmit antenna beam ~or each zone in the point-to-point system in relation to the distance from the center of the beEun in the east-west direction;

Figure 9B is a graph sirnilar to Figure 9A but showing the variation in gain in the north-south direction;

Figure 10 is Q detailed schematic diagram of the filtar 2~ interconnection matrix employed in the point-to point system;

Figure 11 i5 a detailed, plan view of the besm-forming network employed in the point-to-point system;

Figure 12 is an enlarged, irQgmentary view of a portion OI the beam-Ponning network shown in Figure 11;

Figure 13 is a front elevational view of the tran~nit array for the point-to-point system, the horizontal slots in each transmit element not being shown for sake of sirnplicity;

Figure 14 is a side view of the tran~arit element of the array shown in Figure 13 and depicting a corporate feed network for the element;

Figure 15 is a front7 perspective view of one of the trar~mit elements ~nployed ln the transmit array of Pigure 13~

Figure 16 is a front view of the receive feed horns for the point-to-point system; and Figure 17 is a diagr~natic view showing the relationship between a traT~TIitted wave and a portion OI the transnit feed array for the point-to-point system.

DESC PTION OP THE PREFEREED EMBODIMENTS

Referring first to Figures 1-49 a co~munications satellite 10 is depicted which is placed in geosynchronous orbit above the earth's surface. The satellitets ~ntenna system, which will be described in more detail below, will typic lly be mounted on an earth-oriented pl&tfo~n so th~t the antenna system maintains a constant orientation with ao respect to the earth.

The satellite lû is of a hybrid ~omnunic~tions-type satellite which provides two different types of comnunication services in a particular frequency band, for ex&mple, the fi~ed satellite serYiee Ku band. One type of c~nnunicatiorl service, reIerred to hereinafter as point-to-point service, provides two-Yvay comnunicAtions between Yery small apertur~ antenna terminals of relatively narrow band voice and data sigllals. Through the use of frequency division multiple access (FDMA) and reuse of the assigned frequency spectrun, te~ls of thousands of such '~2~

con~nunication channels are ~ccannodated simult~neously on a single linear polarization. The other type of comnunica~ion service provided by the satellite 10 is a broadcast serviee, And it is carried on the other linear polarizationO The broadcast service is primarily used for one-way distribution of video and dat~ throughout the geographic territory served by the satellite 10. As such, the transmit antenna beam covers the entire geogrflphic territory. For illustratiYe purposes throughout this description, it will be ass~ned that the geographic ~rea to be serviced by both the point-to-point and broadcast sèrviees will be the United States~
Accordingly, the broadcast service will be referred to hereinafter as CONIJS (Continental United States).

The antenna system OI the satellite 10 includes a conventional ornni antenna 13 ~nd two antenna subsystems for respectively servicing the point-to-point &nd CONUS systemsO The point-to-point antenna subsystem provides a two-way coJTITlunic~tion link to in~erconnect earth stations for two-way comnunications. The CONUS antenna system functions as a transponder to broadcast, over a wide pattern covering the entire United States, signQls received by one or more p~rticular locations on earth. The point-to-point transmit signal and the CONUS receive signal are vertically polarized. The CONUS transmit and point-to-point receive signals are horizontally polarized. The ~ntenna sys~em includes ~
large reflector assembly 12 canprising two reflectors 12a, 12b. The two reflectors 12a9 12b are rotated relativs to each other about a conanon axis and intersect at their midpoints. The reflector 12a is horizontally polsrized and operates with hori~ontally polarized signals, while the reflector 12b is verticfllly polarized and therefore operates with vertically polarized signals. Conseyuently, eech of the reflsctors 1 2a, 12b reflects signals which the other reflector 12a, 12b tr~nsn~its.

A frequency selective screen 18 is provided which includes two halves or sections 18a, 18b and is mounted on a support 30 such that the screen halves 18a, 18b ~re disposed on opposite sides of a centerline passing di~metrically through the satellite 10, as best seen in Figure 2. The Irequency selective screen 18 flmctions as a diplexer for separating difeerent bands of frequencies and may comprise an array of discrete, electrically conductive elements formed of any suitable materiall such as copper. Any of various types of known frequency selective screens may be employed in this antenna system. However, one suitable frequency selective screen, exhibiting sharp transition characteristics and capable of separating two frequency bands which are relatively close to each other, is described in Canadian Patent Application No. 543,179, filed July 28, 1987, and assigned to Hughes Aircraft Company. The frequency selective screen 18 efEectively separates the transmitted and rPceived signals for both the CONUS and point~to-point subsyst2ms. It may he appreciated that the two halves 18a, 18b of the screen 18 are respectively adapted to se~arate individual signals which are horizontally and vertically polarized.
The CONUS subsystem, which serves the entire country with a single beam, has, in this example, eight conventional transponders each having a high power traveling wave tube amplifier as its transmitter 82 (see Figure 6~. The CONUS receive antenna uses vertical polarization, sharing the vertically polarized reflector 12b with the point-to-point transmission system. CONUS
receive signals pass through the frequency selective screen half 18b and are focused on the receive feed horns 14 located at the focal plane 2$ of reflector 12b.
The antenna pattern so formed is shaped to cover CONUS.
The CONUS transmit antenna employs horizontal 3Q polarization, and shares reflector 12a with the point-to-point receive system. Signals radiatin~ from the transmit feeds 24 are reflected by the horizontally polarized frequency selective screen 18a to reflector 12a whose secondary pattern is shaped to cover CONUS.

~B~2~78 9a The point-to-point subsystem broadly includes a transmit array 20t a subreflector 22, and receive feed horns 16. The transmit array 20, which will be described later in more datail, is mounted on the support 30, immediately beneath the screen 18. The subreflector 22 is mounted forward to the transmit array 20 and slightly below the screen 18. The signal emanating from the transmit array 20 is reflected 1 by the subre~ector 2~ onto one half 18b of the ~creen 18. The subre~ector 22 in conjunction with the ~in reflector 12 functions to effectively mag~fy and enlarge the pattern of the signal e~nating from the tran~nit array 20. The signal reflected fron the subreflector 22 is~
in turn, re~ected by one half 18b of the screen 18 onto the large re~ector 12b, which in turn reflects the point-to-point sign~l to the earth. Through this srrangenent, ths perfo~nance of a large aperture ph~se array is achieved. The receive feed horns 16 Qre positioned in the focal plane 26 of the re~ector 12a. It consists of four m~in horns 50, 54, 58, 62 ~nd three auxiliary horns 52, 56, 60 as shown in Figure 16.

Ref~rring now a~o to Figures 13-15, the tran3nit array 20 c~nprises a plurality, for ex~nple forty, transmit waveguide el~nents 106 disposed in side-by~side relationship to fo~n an array, as shown in Figure 13. Each of the tran~nit waveguide el~nents 106 includes a plurality, ~or ex~nple twenty-six, of horizontal, vertica~y spaced slots 108 therein which result in the generation of a vertica~y polarized signal. As shown in Figure 14, the transmit array 20 is fed wnth a tr~nsmit signal by ~ans of a corporate feed network, genera~y indicated by the nuneral 110 which excites the array element in four places 114.
The purpose of the corporate feed network 110 is to provide a broadband match to the tran~nit waveguide el~nen~ 106. Sign~ls input to the waveguide opening 112 ex~ite the array slots 108 so that the slot excit~tion is designed to ~ive a ~at pattern in the north-south direction.

Attention is now directed to Fig~ e 5 which depicts a gsnera~y rectangu~ar bean cover~ge provided by the horizonta~y polarized point-to-point receive system. In this particul~r exanple, the ~rea serviced by the point-to-point system is the continental United States. The point-to-point receive syst~n c ~ prises four beans R1, R2, R3~ R4 respectively eT~nating fron the four uplink zones 32, 34, 36, 38 to the sate~ite, wherein each of the beans R1-R~ consists of a plurality of individual uplink beRns originating fr ~ individuAl sites in each ~one 32, 34, 36, 38 ~nd carries an individual signal fran that site. The uplink be ~ signals fr ~ the individual sites are Qrranged into e plurality of channels for each zone. For ex~nple, zone 32 may include ~ plurality, e.g. sixte~n 27 MHz channels with each of such channels carrying hundreds of individual bearn signals fran corresponding uplink sites in zone 32.

The sign~l strength for e~ch of the four be~m pattern contours, respectively designated by nurnerals 32, 34, 38 and 38, Rre approximately 3 dB down from peaks of their respective bearns. The antenna beams have been designed to achieve sufficient isolation between them to make feasible in the cross-hatched regions 3~, 41, 43, 45 reuse of the frequency spectr~n four times. In the dotted regions 40, 42, and 44, the isolation is insufficisnt to distinguish between signals of the same frequency originating in adjacent zones. Each signal originQting in these regions will generate two downlink signals, one intended and one extlaneous. The generation of extraneous signals in these ~reas will be discussed later in more detail.

It m~y be readily appreciated fr~m ~igure 5 that the four zones covered by beans 32, 345 36, 38 ~re unequal in width. lhe East Coast zone covered by bearn 32 extends ~pproximately 1.2 degrees;
the Central zone covered by be~m 34 extends approxim~tely 1.2 degrees;
the Midwest rone covered by be~m pattern 36 extends ~ppro~imately 2.0 degrees, and; the West Coast zone covered by be~n pattern 38 extends approxirnately 2.0 degrees. The width of each of the four receive zones 3a, 34, 36 and 38 is detennined by the n~r~er of tem~inals and thus the population density in the various regions of ~he country. Thus3 beam pattern 32 is relatively narrow to accomnodate the relatively high population density in the Eastern part of the United States while beam pattern 36 is relatively ~nde due to the relatively low population density in the Mountain states. Since eAch zone utilizes the entire frequency spectr~n, zone widths sre n~rrower in regions where the population density is highJ to accomnod~te the greater demand ~or channel us~ge.
As shown in Figllre 9, the point-to-point transrnit system comprises four besms T1, T2, T3, T4 respectively covering the four trnnsmit zones 31J :13~ 35, 37, wherein each of the beams T1-T4 consists of a plurality of individual downlink beams destined for the individual downlink sites in each zone 31, 33? 35, 37 and carries an individual signsl to that site. The downlink bearn signals, destined to be received at the individual downlink sites, are arranged into a plurality of channels for e~ch zone. For example, ~one 31 may include a plurality, e.g. sixteen 27 MHz channels with each of such channels carrying hundreds of individual beam signals to corresponding downlink sites in zone 32.

The use of multiple downlink zones and downlink zones of unequal widths assist in causing the inte~nodulation products, generated by the later-discussed solid state power amplifiers, to be geogr~phically dispersed in a manner which prevents most of these products from being received at the ground terminals. The net effect is that the ~mplifiers may be operated more efficiently because the system can tolerate m~re interTodulation products. Although the widths of the transmit zones 31, 33, 35, 37 are neQrly the same as those of the receive zones R1, R2, R3, R4, snall differences between the two sets have been found to optimize the capacity of the system.

The h~lf power beam width of the individual tran~mit be~ms 29 is substantially narrower thun that of the tran~nit zones 31, 33, 35, 37. This results in the desirable high gaiIl~ and avoids the zones of contention 40, ~2, 44 characteristic of the receive zone arrangement.
These individual beuns 29 must be steered within the zones in order to maxi~ze the downlink EIRP in the directions of the individual desffnation tenninals. The transmit point to-point frequency address~ble narrow beams 29 are generated by an array 20 whose apparent size is msgnified by two confoc~ parabolas comprising a main reflector 12b and a subreflector 22. The eRst-west direction of each beam 29 is detennined by the phase progression of its sign~l along the array 106 of transn~it elements 20 (~igures 13 and 15). This phase progression is established by a later-discussed beam~fo~ning network 98 and is a function of the signal frequency. !E3ach of the transmit array elements 20 is driven by æ~

later-discussed solid state power ~nplifier. The power delivered to the array elements 106 is not uniform but is instead tapered with the ed~e elernents being more than 10 dB down. Tapering of the beams 29 is achieved by ~djusting the transmit gain according to the position of the tr&nsmit array elements 20. The excitation pattern determines the ch~racteristics of the transni~t secondary pattern, shown in Figure 9A.
Referring to Figure 9, the elose.st spacing between tran~nit zones 31, 33, 35, 37 occurs between zones 31 and 33 and is approximately 1.2 degrees.
This means that a signal addressed to zone 33 using a particular frequency would interfere with a signal usirlg the sarne frequency in zone 31 with its side lobe 1.2 degrees frorn its beam center. E~owever, the individual transmit gains have been adjusted to provide low side lobe levels thereby pe~nitting frequency reuse adjflcent zone. Referring to Figure 9A, it is seen that the side lobe level at this angle off beam center is more th~n 30 dB down, so that such interference will be negligibly small~ The ssme frequency uses in zones 35 and 37 are further removed in angle, hence the side lobe interference in those zones is even ~maller.

Figure gB is an illustration of the transmit bearn pattern in the north-south direction. The twenty six slots 108 in each of the transmit waveguide elements 10G are excited in ~ manner which creates a nearly flat north-south pattern, extending over the covered range of plus and minus 1.4 degrees Prom the north-south boresight direction.

Both the point-to-point and CONUS systems may utilize the s~rne uplink and downlink frequency bands, with the point-to-point system using horizontal polariz~tion ~or its uplink polarization, and the CONUS system using vertical polarization, as previously mentioned. For exa~rple, both services may, simultaneously, utilize the entire 500 MHz uplink frequency band betYveen 14 and 14.5 GHz9 as well as the entire 500 hSlIz downlink fre~guency band between 11.7 and 12.2 GHz. Each of the recelve zones 32, 34, 36, 38 and trans~nit zones 31, 33, 35, 37, eiTploying the point-to point service utilizes the enffre frequency spectrlDn (i.e. 500 MHz~. Furthermore, this total frequency spectrmn is divided into ~ plurality of channels, for ex~nple, sixteen ch~nnels eQch having a usable bandwidth of 27 MHz and A spacing of 30 r~Hz. In turn, e~ch of the sixteen channels may acco~nodate approximQtely 800 subchannels. Hence, within e~ch ~one, appro~rnately 12,500 (16 channeLs x 800 subchannels~ 32 kilobit per second channels may be aceomnodated, at any gisren moment. As will be discussed below, the comnunication architecture of the point to-point system allows ~ny terlTIinal to caTmunicate directly with any other terminal. Thus, within a single polarization, A total of 509000 subchannels may be accannodated nationwide.

Referring now particularly to Figures 1, 2, 6, 7 and 16, the point-to-point receive feed array 16 employs seven receive horns 50-62. Horns 50, 54, 58 and 62 respectively receive signals frcrn zones 32, 34, 36 and 38. Horns 52, 56 and 60 receive signals from the ones of contention 40, 42 and 44. Using a series of hybrid couplers or power dividers C1-Cg, the signals received by horrLs 50-62 ~re canbined into four outputs 64-70. For ex~nple, a signal originating fran the area of contention 44 and received by horn 60 is divided by coupler C2 and portiorls of the divided signal are respectively delivered to couplers Cl and coupler C4 whereby the split signal is canbined with the incoming signsls received by horns 58, 62 respectively. Similarly, signals originating irom the area of contention 42 ~nd received by horn 56 are split by coupler C5. A portion of the split sign~l is combined, by coupler C39 with the signal output of coupler CJ~9 while the rerr~ining portion of the split signal is combined, by coupler C7, with the sign~l received by horn 54.

Attention is now particularly directed to Figure 6 which depicts, in block di~gram form, the electronics for receiving and transmitting signals for both the CONUS and point-to-point systems. The point-to-point receive signals 64-70 (see also Figure ~) are derived ~r~n the point-to-point receive feed network in Figure 7, whereas the CONUS
receive signal 72 derives fran the CONUS reoeive ~eed horns 14, ~Figures ~39~d8 1 and 3). Both the point-to-point and CONU~ receive signal are inpu.
~o a switching network 76 which selectively connects input lines 64-72 with ~ive corresponding receivers, eight of which re~eivers are generally indicated at 74. The receivers 74 are of eonventionhl design, three of which are provided or redundancy and are not nomally used unless a mslIunction in one of the receivers is experienced. In the event of a rnalfunction, switching network 76 reconnects the appropriate incoming line 64-7~ with a back-up receiYer 74O Receivers 74 function to drivP
the filters in a filter interconnection matrix 90. The outputs of the receivers 74, which are connected with lines 64-70, are coupled by a second switching network 78 through four receive lines R1-R4 to a filter interconnection matrix 90. As will be discussed later below, the filter interconnection matrix (FIM) provides interconnections between the receive zones 32, 34, 36, 38, and the transmit zones 31, 33, 35, 37.
Operating in the above-mentioned 500 MHz assigned ~requency spectrum, separated into sixteen 27 MHz channels, four sets of sixteen fil$ers are employed~ Each set of the sixteen filters utilizes the entire 500 MHz frequency spectr~ and each filter has a 27 MHz banchNidth. As will be discussed later, the filter outputs T1-T4 are arranged in four groups, each group destined for one of the four tranærnit zones 31, 33, 35, 37.

The tr&nsn~it signals T1-T4 are respectively connected9 via switching network g4, to four of six driving ~nplifiers 92, two of such amplifiers 92 being provided for beck-up in the event of failure. In the ev~nt of the failure of one of the alf plifiers 92, one of the be~k-up arnplifiers 92 will be recoImected to the corresponding trensmit sign~l T1-T4 by the switching network 94. A si~dlar switching network 96 couples the empliied output of the amplifiers 92 to a beam-fom~ng network 98.
As will be discussed later in re d~ail9 the beam fomling network 98 consists of a plurality of transmission delay lines ~nnected at equal intervals along the four delay lines. These intervals and the width of the deley lines are chosen to provide the desired centerbend beam squint and the besm scsn rate with freguency for the corresponding transmit zones 31, 33, 35, 37 to be serviced. The tran3nit signals, coupled frcrn the four delay lines9 are swnned in the beem-fo~ning network 98 as shown in Figures 11 Qnd 12, to provide inputs to solid state power ampli~iers 100, which may be embedded in the point-to-point system's trQnsmit array 20. In the illustrated embodiment discussed below, forty solid state power amplifiers (SSPAs) 100 ~re provided. Each of the 5SPAs 100 arnplifies fl corresponding one OI the forty signals forrned by the be~n-forming network 98. The SSPAs 100 possess dif~erent power capacities to provide the tapered array exc!itation previously mentioned. The output of the SSPA 10a is connected to the input 112 (Figure 14) at one of th el~nents OI the transmit array 20.

The receive signal for CONIJS on line 72 is connected to an appropriate receiver 74 by switching networks 76, 78. The output of the receiver connected with the CONUS si~nal is delivered to an input multiplexer 80 which provides for eight channels, as mentioned aboYe.
The purpose of the input multiplexers 80 is to divide the one low level CONUS signal into subsignals so that the subsignals can be amplified on an individual basis. The CONUS receive signals are highly arnplifled so that the CONUS trar~nit signal may be distributed to very snall earth terminals. The outputs OI the input multiplexer 8Q ~re connected through a switching network 84 to eight of twelve high power traveling wave tube amplifiers (TWTAs) 82J four of which TWTAs 82 are ~nployed for b~ck-up in the event of fQilure. The outputs o the eight TWTAs 82 are connected through another switching network 86 to an output mutliplexer 8~ which recon~ines the eight ~nplified signals to form one CONUS
transmit signal. The output of the multiplexer 88 is delivered via waveguide to the trar~mit horns of the CONUS trarE;mitter 24 (Figures 2 and 3)~

Attention is now directe~ to ~igure 10 which depicts the details of the FIM 90 (Figure 6~. As previously discussed, the FlM
90 ef~ectively interconnects any temunal in any o~ the receive zones 32, 34, 36, 33 (Figures 5) with any tem~inal in any of the transnlt zones 31, 33, 359 37. The FIM 93 includes four waveguide inputs 120, 122, 124 and 126 for respectively receiving the receive signals :E~l, R2, R3 Rnd R4.
As previously mentioned, receive signals Rl-R4., which originate fran a corresponding receive zone 32, 34, 36, 38 (Figure 5), e~ch contain the entire assigned frequency spectr~n, (e.g. 500 MHz), and flre sepflrated into a plurelity of ch~nnels, (e.g. sixteen 27 MHz channel~). The channels are further separated into a plurality of subchannels, where e~ch of the subchannels c~rries a signal fran a corresponding uplink site.
The FIM 90 includes 64 filters, one of which is indicated by the n~neral 102. Each of the filters 102 has ~ passband corresponding to one of the chQnnels te.g. 1403-1430 MHz). The filters 102 are arranged in four groups, one for each receive zone 32, 34, 36, 38, wi$h each group including two banks or subgroups of eight filters per sl~bgroup. One subgroup of filtPrs 102 contains those filters for the even-n~nbered channels and the other subgroup in each group contains eight filters for the odd- mnnbered channels. Thus, for ex~rnple7 the filter group îor receive signal R1 cornprises subgroup 104 o~ filters 102 for odd channels, and subgroup 106 of ~ilters 102 for ~ven ch~nnels. The foLlowing table relates the receive sign~ls and zones to their filter subgroups:

Filter Sub~rou~s Receive Zone eceive S~nal Odd Channels Even Chlmnels 38 ~4 116 118 The filters are grouped in a unique mQnner such th~t when the receive signals R1 R4 are filtered, the filtered outputs sre con3bined to ~olm the tr~nsmit signalsO The transmit signals T1-T4 also utilize the entire assigned frequency spectrun, (e.g. 500 MHz~. In the illustrated ~nbodiment~ each of the tra~nit signals T1 T4 possesses sixteen 27 MHz wide channels, and cornprises four channels fran each of the four receive ~one~ 32-38 ~Figure 5).

The in~aning receive sign~ls R1-R4 are divided into the corresponding subgroups by respectively associated hybrid couplers 128-13~ which effectively divert 50% of the signal power to each subgroup. Hence, for ex~rnple, one-half of the Rl signal input at waveguide 12û is diverted to tran~nission line 136 which services the subgroup 104 of filters 102, and the r~naining hslf of the Rl signal i3 diverted to transmission line 138 which services subgroup 106 of filters 102. In a similar manner, each of the subgroups 1û4-118 of filters 102 is served by a corresponding distribution line, sirnilar to lines 136 and 138.

The construction of subgroup 104 wiLll now be described in more detail, it being understood that the resnEIining subgroups 106-118 are identical in architecture to subgroup 1û4. At interv~ls along the transmission line 136, there are eight ferrite circulators 140, one associated with each of the odd-nurnbered channel filters 102. The function of the circulators 140 is to connect the transmission line 136 to each of the odd channel filters 102 in a lossless m~nner. Thus, for ex~3nple, the Rl signal enters the first circulator 140a and circulates it counterclockwise whereby the 27 MHz band of signals corresponding to channel 1 passes through it to circulator 142. All other frequencies are reflected. These reflected signals propagate via the circulator toward the next filter where the process is repeated. Through this process, the Rl receive signal is filtered into sixteen channels by the sixteen filters 104-108 corresponding to the Rl signals. Hence, the R1 signal with frequencies in the range of channel 1 will p~ss through the first ferrite circulator 140a and it will be filtered by Iilter 1 of group 104.

The outputs frcm a filter subgroup 1û4-118 are s~lectively coupled by a second set of ferrits cir~ulators 142 which s~s, in a criss-cross pattern, the outputs fran An adj~cent group of filters 102. For e2tarnple, the outputs of ch~nnel filters 1, 5, 9, and 13 of group 104 are s~med with the outputs of channel filters 3, 7, 11 and 15 of filter group 112. This smn appe~rs at the output tem~inal for Tl 144.
Referring to Figure 8, these sign~ls correspond to the ~onnections b~tween re~eive ~.ones Rl and R3 ~nd to tra~nit zone Tl.

Attention is now directed to ~igures 8 Hnd 9 ~hich depict how the tr~nsmit and receive signals are interconnected by the FIM 90 to ~llow two-way caTsnunication between any te~ninals.
Specifically, Figure 8 provides a table showing how the receive and transmit zones are connected together by the interconnect channels while Figure 9 depicts how these interconnec~ channels are distributed geographically across the transmit zones 31, 339 35, 37. In Figure 8, the receive signals R1-R4 are read across by rows of interconnect channels and the tran~nit signals T1-T4 ~re read by col~Tms of intereonnect 10 channels. It e~n be readily appreciated fran Figure 8 that each of the transrnit signals T1-T4 is made up of sîxteen channels ~rrenged in four groups respectively, where e~ch group is associated ~nth one OI the receive signals Rl-R4. The s~tellite co Tmunications system of the present invention is intended to be used in conjunction with a ground 15 station referred to as Q satellite network control center which coordinates comnunications between the ground tenninals via packet switched signals. The network control center assigns an uplink user with an uplink frequency based on the location of the desir~d downlink, assigning the available frequency whose downlink longitude is closest to 20 that of the destination. The frequency addressable downlink transmit bea~ 29 are thus ~ddressable by the frequencies of the uplink signals.
This strategy maximizes the gain of the downlink signal.

As shown in Figure 9, the continental IJnited States is divided into four primary zones 31, 33, 35, 37. Zone 31 may be referred 25 to as the East Co~st zone, zone 33 is the Central zone, zone ~5 is the ~/lountain zone, and zone 37 is the West Coast zone. As previously mentioned, each of the zones 31, 33, 35, 37 utilizes the entire assigned frequency spectr~n (e.g. 500 MHz~. Thus~ in the case of a S00 MHz assigned frequency band, there ex~sts sixteen ~7 MHz channels plus guard 30 bands in each of the zones 31, 33, 35, 37.

The n~nbers 1-16 repeated four ~mes above the be~m;
29 in Figure 9 indicate the longitude of the be~rns corresponding to the center frequencies of the channels so n~nbered. BecQuse of the ~ ;~d ~ ~,''7 ~3 frequency sensitivity of the bearr~, the longitude span between the lowest and highest ~requency narrow band signal in a channel is approximately one channel width. Each beam is 0.6 degrees wide between its half power point, about half the zone width in the East Co~st and Central zones ~nd nearly one-third the zone width in the Mountain and West Coast zones.
The antenna bearns 29 overlap each other to ensure a high signal density;
the re that the beams overlap, the ~rea$er channel capacity in a given area. EIence, in the East Coast ~one 31, there is a gre~ter overlap than in the Mountain zone 35 because the signal traffic in the East Coast zone 10 31 is considerably greater than that in the Mountain zone 35.

The interconnect scheme described ~bove Mll now be explained by way of a typical ~omnunication between terminals in different zones. In this ex~mple, it w~ll be assum~d that a ~aller in Detroit, Michigan wishes to place a eall to a te~ninal in Los Angeles9 15 California. Thus, Detroit, Michigan, which is located in the Cerltral zone 34, is the uplink site, and Los Angeles~ C~lifornia, which is 1Ocated in the West Coast zone 37, is the downlink destination~ As shown in Figure g, each geographic location in the continental United States can be associated with a specific channel in a specific zone. Ttlus, Los Angeles 20 ls positioned between ch~nnels 14 and 15 in tr~nsmit zone 37.

Referring now concurrently to ~igures 5, 8 and 9 particularly, receive and trar~nit zones Rl and T1 lie within the East CoRst zone 32 ~nd 31, R2 and T2 lie within the Central zone 34 and 33, R3 and T3 lie within the Mountain zone 36 and 35, and R4 and T4 lie 25 within the West Coast ~one 38 ~nd 37~ Since Detroit lies in the Central or R2 zone 34, it can be seen that the only channels over which signals can be transrnitted to the West Coast or T4 zone 37 are channels 1, 5, 9 and 13. This is dete~nined in the table of Figure 8 by the intersection of row R2 ~nd col~nn T4. ThereIore, from Detroit, the uplink user would 30 uplink on either channel 1, 59 9 or 13, whichever of these ch~nnels is closest to the downlink destination. Since Los Angeles is locdted bet~een chann~ls 14 Qnd 159 the network control center would uplink the sign~l on channel 13 beeause ch~nnel 13 is the close~t to ch~nnel 14.

--21~
The downlink bearn width is broad enough to provide high ~Qin at Los Angeles.

Conversely, if the uplink site is in Los Angeles and the downlink destination is in Detroit, the intersectivn oî row R4 and col~nn S T2 in Figure 8 must be consulted. This intersection reveals that the signal can be transmi~ted on channels 1, 5, ~ or 13 depending upon which channel is closest to the downlink destination. The network control center would uplink the signal from Los Angeles on channel 9 since channel 9 is closest to ch~nnel 11 which, in tUl'n9 iS closest to Detroit.

Returning now to Figure 10, the eonversion of a receive signal to a transmit sig3lal will be described in connection with the ex~nple mentioned above in which the uplink site is in Detroit and the dowrlink site is in Los Angeles. The uplink signal tran~mitted frcm Detroit would be tran~;rnitted on channel 13 carried by r2ceive signal R2.
Thus, the R2 receive signal is input to transmission line 122 and a porffon of such input signal is diverted by the hybrid coupler 130 to the input line of subgroup 108 of filters 102. Subgroup 1û8 includes a bank of eight filters for the odd channels9 including channel 13. Thus, the incoming sign~l is ~iltered through by filter 13 and is output on a line 164 2~ along with other signals from subgroups 108 and 116. The ~hannel 13 signal present on line 164, is canbined by the hybrid coupler 153, with signals emanating from subgroup 106 ~nd 114, and fo~ns the T4 sign~ cn output line 15û. The transmit signal T4 is then downlinked to Los Angeles.

It is to be understood that the above ex~mple is samerihat simplified ina~much as the network control center would assign a more specific chQnnel thRn a 2~ MHz wide bQnd cha~mel, since the 27 MHz wide ch~nnel may actuslly c;xnprise ~ mulffplicity of sm~ller channels, for e~mnple, ~Oû subch~nnels of 32 KH2 bandwidth.

Referring now Q~ain to ~igures 5, B and 9, in the event that an uplink ~ign~l originates from one of the ~Pe~ of contenffon, 401 42, ~4 (Figure 5), such signal will not only be tran~nitted to its desired downlink destination, but a non-neglible signal will be transmitted to another geographic area. ~or example, ass~ne that the uplink signal originates frcm Chicago, Illinois which is in the area of contention 42 and th~t the signal is destined for Los Angeles, California. The area of contention 42 is produced by the overlap of the be~rns forning zones 34 and 36. Hence, the uplink signal can be transrnitted as receive signals R2 or R3. The network control center determines whether the uplink comnunication is carried by receive signals R2 or R3. In the present example, since Chicago is closer to zone 36, the uplink c~mnunication is carried on receive signal R3.

As previously discussed, the downlink desffnation, Los Angeles, is located in zone 37 and lies between channels 14 and 15. As shown in Figure 8, the intersection of R3 with colu~ T4 yields the possible ch3lmels over which the clxTmunication can be routed. Thus, the Chic~go uplink signal will be transmitted over one of ¢hannels 2, 6, 10 or 14. Since Los Angeles is closest to channel 14, channel 14 is selected by the network control center as the uplink channel. Note, however, that an undesired signal is also transmitted fr~n zone 34 on chflnnel 14.
To determine where the undesired signal will be downlinked, the table of Figure 8 is consulted. The table oî Figure 8 reveals that uplink signals carried on ch~nnel 14 in ~he R2 ~one 34 ~re downlinked to the T1 transrnit zone 31. The desired signal is transmitted to Los Angeles and the undesired signal (i.e. an extraneous signal3 is transmitted to the East Coast (i.e. ~one 31). The network control center keeps track of these extraneous signals when m~king frequency assigr~nents. The effect of these extraneous signals is to reduce slightly the capHcity of the syst~n.

Referring now again to Fi~ure 6, the bessn-Ionning network 98 receives the transmit signals T1-T4 and flmctions to couple aLI of the individual comnunication sign~ls in these tr~n3nit signals together so that ~ tran.~nit antenna bearn for each signal is formed. In the exsmple disc~ssed above in which the ~ssigned frequency spectrun is 500 MHz, a total of approximately 5û,000 overlQpping antenna beams are fo~ned by the beam-forming~ network 98 when the system is fully loaded with narrow band signals. Ench antenna be~un is fo~ned in a manner so th~t it can be pointed in a direction which optimizes the perforsnance of the system. The incremental ph~se shift between adjacent el~nents dete~nines the direction of the antenna bea~T. Since this phase shift is determine~ by the signal frequency, the systern is referred to as frequency addressed.

Attention is now direeted to Figures 11 ~nd 12 which depict the details of the besm-fo~ning network 98. The be~m-forming network, genera~ly indichted by the nmneral 98 in Figure 11, is ~rrQnged in the general form of an arc ~nd may be conveniently mounted on the comnunic~tion shelf (not shown) of the s2tellite. The ~rc sh~pe of the fo~ning network 98 facilitates an arrangement which ~sures that the paths of the signals passing therethrough are of correct length.

The beam forming network 98 includes a ~irst set of circunferentially extending transmission delay lines 168, 170, a second set of tr~nsmission del~y lines 172, 174 which are radially spaced fran delay lines 16B and 170, and a plurality of radiQlly extending waveguide assemblies 176. In the illustrated embodiment9 forty waveguide ass~nblies 176 are provided, one for each of the elements 106 of the transmit array 2U (Figure 13~. The waveguide ass~nblies 176 intersect ea~h of the delay lines 168-174 and are equally sp~ced in angle.

Each of the waveguide ~ssemblies 17~ defines a radial line summer and intersects each o~ the delay lines 168-174. As shown in Figure 12, at the points of interssction, between the radi~l line s~mers 176 and the transmissisn delay lines 188-174, a crossguide coupler 180 is provided. The cro6sguide coupler 180 connects the del~y Lines 16B-174 with the radi~l line sunners 176. The function of ths crossguide couplers 180 will be disc~Lssed later in n~re detail.

Four delay lines 168-174 are provided respectively for the four trarEanit zones Tl-T4 (Figure 9). Hence, transn~it signal T1 is ao~

1 provided to the input of delay line 170, T2 is provid~d to input of delay line 168, T3 is provided to the input of delay line 174, 2nd T4 is provid~d to the input of del~y line 172. As shown in Figure 12, the dist~nce between the radial line sumners is indicated by the letter "1" and the s width of each of the r~dial delay lines is designated by the letter ~w~.Although the radial line sunmers 176 ~re sp~ced at equ~l angu1ar intervnls along the delay lines 168 174, the d~tance between them varies fron delay line to delay line due to the fact that the delay lines 168-174 are radia~y spaced fron each other. Thus, the further from the center of the arc, which is fo~ned by the radial line sunxners 176, the greater the distance between the radial line sunrners 176, at the point where they intersect with the delay lines 16B-174. In other words, the spacing ~l"
between radial line sunlners 1~6 for delay line 168 is less than the spacing between adjacent r~dial line sumners 176 than for delay line 174.
Typica1 vrlues for the d~nensions ~l" and "w~ are ~s follows:

Delay Line ~ 2~

168 T2 1.66 0.64 170 T1 1.72 0.66 172 T4 2.45 0.74 174 T3 2.55 0.76 The width of the delay lines 168-174, "w", snd the distance ~1" between ~djacent radial line s~nners ~re chosen to provide the desired center be ~ squint and be ~ scan rate so that the beam pninting is correct for ea~h ch~nnel. This results in the desired st~rt ~nd stop points for e~ch of the tr~n3nit 7ones T1-T4.

Referring partieularly to Pigure 12, the tr~n~nit signa1 T2 propagates down the delay ~ne 1~8 for a preeise d~tance, ~t which point it reQches the f~st radia1 line su~mer 176. A porffon of the T2 signal p~sses through the cro6sguide ~oupler lr,0, which nn~y, for exaTple, be ~ 20 dB coupler, such that one percent of the tr~nsmNtted pcwer of tr6nsmut sign~l T2 is diverted down th~ r~dial line sunnner 176. This diverted energy then prop~gates down the waveguide 176 towards a corresponding solid state power flrnplifier 100 (Figures 6 Qnd 11). This process is repeated for signal Tl which propagates down del~y line 170.
The portions of signals T1 ~nd T2 which are dive~ted by the crossguide couplers 180 (i.e~ 0.01 Tl and 0.01 T2) are surnned together in the radial line summer 176 and the eombined signal O.G1 (T1 + T2) propagates radially outwardly toward the next set of delay lines 172, 174. This same coupling process is repeated for signals T3 and T4 in delay lines 174 and 172 respectively. That is, 0.01 o~ signals T3 and T4 are coupled via crossguide couplers 180 to the r~dial line sumner 176. The resulting cornbined sign~l 0.01 (Tl ~ T2 + T3 ~ T4~ propagates radially outwardly to an associated solid state power ~Tplifier 100 where it is amplified in preparation for tran~nission.

After encountering the first radial line sumner 176, the remainirg 0.99 of signals T1-T4 propagate to the second radial line sumner where an additionPl one percent of the signals is diverted to the s~Tner 176. This process of diverting one percent of the signals T1-T4 is repeated for each of the radi~] line sunmers 176.

The sign~ls, propagating through the radial line sumners 176 towards the SSPAs 100, are a mixture of all four point-to-point transmit signals Tl-T4. However, each of the trar~nit signals T1-T4 may comprise 12,500 subsignals. Consequently, the forty signals propagating through the radiel line s~Tmers 1~6 m~y be a n~ixture of Qll 5û,000 signals in the c~se of the embodiment mentioned above where the ~ssigned f equency spectr~n is 500 MHz wide Therefore, each of the SSPAs 100 arnpli~ies all 50,000 signflls which ern~nate frorn each of the plurality of wave guide assemblies 176.

Since each of the SSPAs 100 amplifies all 50,000 signals which are destined ~or ~1l regions of the country, it can be appreciated that all of the narrow, high gain downlink hearns are fom~ed frn a cornrnon pool of transmitters1 i.e. Qll OI the S~PAs 100. This ~rrangement may be thought oi as ~ffectively providing ~ n~tionwide pool of power 37~

since each of the downlink be~ms covering the entire country is produced using all of the SSPAs 100. Consequently, it is possible to divert a portion of this nationwide pool of power to accomnodAte specific, disadvantaged downlink users on an individufll bssis without materially reducing the signsl power of ~he other bean~. For example, a downlink user may be 'idisadvantaged" by r~in in the downlink destination which attenuates the signal strength of the beam. Such a rain disadvantaged user n~y be individually accomTlodated by incre~sing the signal str~ngth of the corresponding uplink bea3n. This is accoraplished by diverting to the disadvantaged downlink beam, a sma~l portion of the power fran the pool of nationwide transmitter power (i.e. a fraction of the power supplied by all of the SSPAs 100). The power of an individual uplink bearn is proportional to that of the corresponding downlink beArn.
Consequently, in order to increase the power of the downlink besrn it is merely necessary to increase the power of the uplink be~m.
In practice, the preYiously mentioned network control center keeps track OI all of those regions of the country in which it is raining and determines which of the uplink users are placing caTmunications to downlink destinations in rain ~ffected ~reas. The network control center then instructs each of these uplink users, using p~cket switched signals, to increase its uplink power for those signals destined for a rain affected area. The increase in power of the uplink user's signals results in greater collective ampli~ication of these signals by the SSPAs 100, to produce corresponding downlink beams to the rain affected areas, which have power levels Increased sufficiently to cnmpensate for rain attenuatiorlO Typically, the n~ber of si~nals destined for rain affeeted areas is smflll relative to the total nunber of signals being hEmdled by the total pool of SSPAs 100. Accordingly, other downlink users not in the r~in ~ffected zones do not suffer substantial si~l loss sin~e the ~all loss th~t m~y oc~ur in their sign~ls is spread out over the mQny thousand users.

The SSPAs 100 (Figures 8 and 11~ rnay be mountedl for ex~nple, on the rim of the camnuni~ation shelf (not shown) of the -27~
satellite. Th~ signals ~rnplified by the SSPAs 100 are fed into the corresponding el~nents 106 of the transrnit array 20 (Figure 13 and 14~.

As previously discussed, an incremental ph~se shift is achieved between the signals thut are coupled in the forty ra~isl line s~ners 1~6. Hence, the beam-fonning network 98 permits the antenna be~rs eman~ting fran the transnit arr~y 20 (Figures 1, 2, and 13) to be steered by freguen~y ~ssigr~ent, The incr~ntal phase shift i~ related to the time delay between the waYeguides 176 as well as frequency.
Attention is now directed to Figure 17 which is ~ diagrarnn2tic view of four of the forty transmit array elements 106 (~igure 13), showing the waYefFont ~nating therefram, wherein "d" is equal to the spacing between transmit ~rray elements 106. The resulting antenna beam h~s ~n angular tilt of a , where ~ is defined as the beam scan angle. This means that ~ is the angle fram normal of the transrnit be~n ~enter.
The incremental phase shift produced by the delay line arrangement is a~
The relationship between ~ ~ ~3d ~ is giYen by ll ~ = ~ 8i11 ~) where:
~ = signal wavelength 9 = be~rn scan ~ngle d = spacing between Qrr~y elements Hence7 the east-west direetion of the ~ntenna beam is detennined by the ineremental ph~se shift which is different for the four delay lines 1~8-174 of the besm-folsning network g8, resulting in the four tr~r~mit ~ones Tl-T4 previously noted, Having thus described the inYention, it is recogniz~d th~t those ~killed in the art msy rr~ke ~arious n~ficRffons or additions to the pre~erred ~odiinent chosen to illustrate the invention without 3~ 8~ ~

departing from the spirit and scope of the present contribution to the art. Accordin~ly, it is to be understood that the protection sought ar,d to be afforded hereby should be deffned to extend to the subject matter claimed and all equivalents thereof fairly wnthin the scope of the 5 invention.

Claims (7)

1. Apparatus for communicatively interconnecting any of a plurality of terminal sites within an area on the earth, comprising:
a satellite positioned above the earth;
means carried by said satellite for respectively receiving from uplink terminal sites in said area a plurality of uplink radio frequency beams each carrying a receive signal;
means carried by said satellite for converting said receive signals into transmit signals each including a plurality of corresponding subsignals destined to be received at downlink terminal sites in said area by changing the frequencies of said receive signals;
a plurality of amplifiers carried by said satellite for collectively amplifying all of said transmit signals such that each of said transmit signals is amplified by all of said amplifiers; and means carried by said satellite for forming a plurality of downlink radio frequency beams each carrying one of said transmit subsignals destined to be received by one of said downlink terminal sites and primarily covering only a portion of said area, said beam-forming means including -(1) a first plurality of lines for respectively carrying said transmit signals, and (2) a second plurality of spaced apart lines intersecting said first plurality of lines at crossover points and extending radially from a reference point so as to diverge from each other, each of said second plurality of lines being coupled with each of said first plurality of lines at said crossover points such that a portion of the energy of each of the transmit signals carried by each of the first plurality of lines is transferred to each of said second plurality of lines, each of said second plurality of lines having an output for outputting all of said transmit signals, each of said outputs being associated with and coupled to one of said amplifiers such that each of said amplifiers amplifies all the transmit signals from an associated one of said amplifiers; and means carried by said satellite for respectively transmitting said downlink beams to corresponding portions of said area.
2. The apparatus of Claim 1, wherein said first plurality of lines extend circumferentially about said reference point and are radially spaced relative to said reference point such that the distance between adjacent crossover points increases with increasing radial distance of the crossover points from said reference point.
3. The apparatus of Claim 2, wherein at least certain of the lines in said first plurality of lines are unequally radially spaced apart from each other.
4. The apparatus of Claim 2, wherein said first plurality of lines includes a first set of essentially contiguous lines and a second set of essentially contiguous lines spaced apart from said first set thereof.
5. Apparatus for communicatively interconnecting any of a plurality of terminal sites within an area on the earth, comprising:

a satellite positioned above the earth;
means carried by said satellite for respectively receiving from uplink terminal sites in said area a plurality of uplink radio frequency beams each carrying a receive signal;
means carried by said satellite for converting said receive signals into transmit signals each including a plurality of corresponding subsignals destined to be received at downlink terminal sites in said area by changing the frequencies of said receive signals;
a plurality of amplifiers carried by said satellite for collectively amplifying all of said transmit signals such that each of said transmit signals is amplified by all of said amplifiers; and means carried by said satellite for forming a plurality of downlink radio frequency beams each carrying one of said transmit subsignals destined to be received by one of said downlink terminal sites and primarily covering only a portion of said area, said beam-forming means including -(1) a first plurality of lines for respectively carrying said transmit signals, and (2) a second plurality of spaced apart lines intersecting said first plurality of lines at crossover points and extending radially from a reference point so as to diverge from each other, each of said second plurality of lines being coupled with each of said first plurality of lines at said crossover points such that a portion of the energy of each of the transmit signals carried by each of the first plurality of lines is transferred to each of said second plurality of lines, each of said second plurality of lines having an output for outputting all of said transmit signals, each of said outputs being associated with and coupled to one of said amplifiers such that each of said amplifiers amplifies all the transmit signals from an associated one of said amplifiers, said first plurality of lines extending circumferentially about a reference point and being radially spaced relative to said reference point such that the distance between adjacent crossover points increases with increasing radial distance of the crossover points from said reference point: and means carried by said satellite for respectively transmitting said downlink beams to corresponding portions of said area.
6. The apparatus of Claim 5, wherein at least certain of the lines in said first plurality of lines are unequally radially spaced apart from each other.
7. The apparatus of Claim 5, wherein said first plurality of lines includes a first set of essentially contiguous lines and a second set of essentially contiguous lines spaced apart from said first set thereof.
CA000543176A 1986-08-14 1987-07-28 Satellite communications system having multiple downlink beams powered by pooled transmitters Expired - Lifetime CA1282878C (en)

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US896,910 1986-08-14
US06/896,910 US4831619A (en) 1986-08-14 1986-08-14 Satellite communications system having multiple downlink beams powered by pooled transmitters

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EP (1) EP0277188B1 (en)
JP (1) JPH01500953A (en)
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US4831619A (en) 1989-05-16
JPH01500953A (en) 1989-03-30
DE3781395D1 (en) 1992-10-01
WO1988001454A1 (en) 1988-02-25
DE3781395T2 (en) 1993-04-01
EP0277188A1 (en) 1988-08-10
EP0277188B1 (en) 1992-08-26
CN1008678B (en) 1990-07-04
CN87105576A (en) 1988-05-11
JPH0552099B2 (en) 1993-08-04

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