US2839729A - Multi-mode waveguide system - Google Patents

Description

June 17,1958 GIBSON 2,839,729

MULTI-MODE WAVEGUIDE SYSTEM Filed Feb. 15, 1954 v 2 Sheets-Sheet 1 Hen/i:- mpur A IN V EN TOR. JOHN .1 6/550 MM [6M June 17, 1958 J. J. GIBSON MULTI-MODE WAVEGUIDE SYSTEM 2 Sheets-Sheet 2 Filed Feb. 15. 1954 7'0 i/Y/i/Y/Yfl Jaw/b 62%; Mr

INVENTOR.

2,839,729 MULTI-MODE WAVEGUIDE SYSTEM John 3'. Gibson, Princeton, N. .L, as signor to Radio Corporation of America, a corporation of Delaware Application February 15, 1954,.Serial No.f41o,302

The terminal fifteen years ofthe term of :thepat'ent to be granted has been disclaimed 11 Claims. (Cl. 333-6) This invention relates 'to a multi-mode waveguidesystern, and particularly to means providing separate couplings for each of three decoupled signals in a single waveguide. A different construction for a similar purpose is shown in Patent No. 2,709,240, issued to me on May 24, 1955. r 1

While not limited thereto, this invention is particularly useful in the field of television broadcasting where separate transmitters are used to generate the sound-modulated and the picture-modulated radio frequency signals, and a single antenna is employed to radiate the combined or composite radio frequency signal. It is important that the means for coupling the two transmitters to the common antenna be such as to isolate the transmitters from each other, and to direct energy reflectedtrom the antenna (clue to mismatch) to a soak-up resistor rather than back to the picture transmitter.

A very effective way to feed high power ultra-high frequency signals to a radiating antenna is by'means of awaveguide. A waveguide can transmit very high power, and at ultra-high frequencies, waveguides have moderate physical dimensions which make'them inexpensive and practical. Ultra-high frequency antenna arrays preferably include waveguide systems having a' plurality of radiating slots, or dipoles or monopoles. One such antenna is shown and described in the U, S. Patent No. 2,807,018 issued to Oakley M. Woodward, Jr., onSeptember 17, 1957. The waveguide system of this invention is particularly useful in coupling two transmitters to an an tenna array of the type including a central waveguide from which energy is coupled to the-radiating elements of the antenna array. 1 I

An object of the invention isto provide a diplexer for I combining two separate radio frequency signals in a single waveguide.

Another object of this invention is to provide an ,im-

proved. system employing separate couplings for each of three decoupled signals in a single waveguide;

Itis another object to provide an improved single waveguide system within which three decoupled signals may be propagated, and three individual transmission l'mes connected to the single waveguide to selectively couple thru the three signals in the single waveguide.

It is a further object to provide a waveguide system including a generally circular waveguide whichat one end forms an integral part of an antenna array and which at the other. end is connected to three rectangular waveguides, two of which are adapted to be connected to the respective outputs of two radio transmitters, and the third of which is adapted :to be connected to a soakup resistor which absorbs energy reflected back from the antenna. Y

It is a still further object to provide an improved wave: guide system for coupling the outputs of two transmitters to a single generally-circular waveguide extending a considerable distance to an antenna array.

In one aspect, the invention comprises a generallvcircular waveguide capable of propagating the TB mode a 2,839,729 Patented June 17, 19.58

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' cu1ar or polygonal cross-section. One form of generally circular waveguide has a square cross-section. A generally circular waveguide having an octagonal cross-section may advantageously be employed. The upper end of the generally circular waveguide may be connected to an antenna array. The other end of the generally circular waveguide is connected thru a transformer ta tapered section) to a rectangular waveguide which may, at the other end, be connected to the output of a picture signal transmitter. A magic T is arranged with .respect to the generally circular waveguide so that the main wave guide of the magic T is formed around the generally circular waveguide, the E- plane arm extends out at right angles with the axis of the generally circular waveguide, and the H-plane arm of the magic .T extends downwardly in parallel spaced relation with the rectangular waveguide connected to the picture transmitter. The H-plane wave guide is adapted to be connected to the output of a sound signal transmitter, and the E-plane waveguide is adapted :to be connected to a soak-up resistor "for absorbing enetgy-reflecte'dtrom the antenna array. Meansare provided :for coupling energy from the main waveguide of the magic T at points equi-distant from the junction to points on opposite sides in the generally circular waveguide.

In another aspect, the waveguidesystern utilizes a generally circular waveguide having a coaxial inner conductor so that the generally circular waveguide is capable of propagating the TE mode and the TEM or coaxial line mode. In both forms of the invention, the generally circular waveguide is adapted for the propagation of two decoupled signals in the TE modes, the two modes be ing oriented atright angles with each other. These and other objects and aspects of the invention will be apparent to those skilled in the art from the following more detailed description taken together withthe appended drawings wherein: e

Fig. l is a perspective view, partly broken away, of a waveguide system constructed according to the teachings of this invention and including a generally circular wave guide which is circular or cylindrical in form;

Fig. 2 is a transverse cross-sectional view taken on the line 22 of Fig. 1;

Fig. 3 is a perspective view, partly broken away, of a multi-mode waveguide system utilizing a generally circular waveguide of square cross-section, and including .a coaxial inner conductor;

Fig. 4 is a transverse sectional view'taken on the line 4.-4 of Fig. 3; and

Fig. 5 .is a transverse sectional view taken on the line 5-5 of Fig. 3.

.array.

.A magic T includes a main rectangular waveguide 13, an E-plane rectangular waveguide arm 14, and an H;- plane rectangular waveguide-arm-IS. A known-magic 'I is shown and described starting on page 259 of :volume 16, Microwave Mixers, of the Radiation. Laboratory Series, 1948. The magic T has a main rectangular waveguide extending .in a straight l-ineatright an les with both the E-plane arm and the H-plane arm. A-

cording to the present invention, the main waveguide 13 is formed around the generally circular waveguide 10. The E-plane arm 14 is adapted for connection to a soakup resistor, and the H-p'lane arm 15 is adapted for connection to the output of a sound signal transmitter of a television station. r 7 Energy is coupled from the main waveguide 13 to the interior of the generally circular waveguide by means of probes 16 and 17 extending thru apertures 18'and 19, respectively, into the interior of the generally circular waveguide 10. Itwill be noted that the probes 16 and 17 are equi-distant from the junction 20 of the magic T. The ends of the main waveguide 13 are short-circuited at 21 and 22 at distances which are electrically in the v order of a quarter-wavelength from the probes 16 and 17, respectively. I

In the operation of the multi-mode waveguide system shown in Figs. 1 and 2, as applied to a television transmitting system, energy in the TE mode from the picture transmitter is applied thru rectangular waveguide 12, and :thru' tapered portionll to excite the TB mode in the generally circular waveguide 10. This energy is propagated up the generally circular waveguide 10 to the antennaarray from which it is radiated into space. The generally circular waveguide 10 includes fins (not shown) which translate the linearly polarized TE mode to a circularly polarized'TE mode at the antenna. A small amountof energyis reflected back down the generally circular waveguide 10 because, in practice, it is difiicult to match'the antenna to the circular guide over a broad frequency band. The reflected energy is translated back to a linearly polarized TE mode by the fins.

The incident TE mode in the generally circular waveguide 10 is so oriented that it does not couple to the probes 16 and 17. The reflected TE mode, however, is polarizedat right angles to' the incident wave, due to the action of the fins, so that reflected energy is coupled thru the probes 1'6Iand 17 to the two ends of the main waveguide 13 of the magic T. At an instant of time, the reflected TE mode in the generally circular waveguide 10 couples the positive potential to probe 16 and a negative potential to probe 17. This results in energy flowing from the two ends of the main waveguide 13 toward the junction from which the'energy is coupled to the -E-plane waveguide 14. The waveguide 14 is connected to a soak-up resistor which absorbs the energy reflected from the antenna. The reflected wave in the rriain waveguide 13 is sooriented that it cannot couple to the H-plane waveguide 15 which is connected to the sound transmitter. Energy from the sound signal transmitter is applied in the TE mode thru the H-plane waveguide 15 to the junction point 20 of the magic T. From the junction 20, the energy divides in both directions along the main waveguide 13 and excites the probes 16 and 17. The

probes. 16 and 17, at an instant of time, are both excited positively. The energy is therefore such as to excite the TM v mode in the generally circular waveguide 10. This energy is propagated up the generally circular waveguide -10 to the antenna from which it is radiated into space. The sound signal energy in the H-plane waveguide 15 is so oriented that it cannot couple to the E-plane arm 14. The sound signal energy in the generallycircular waveguide 10 is in the TM mode and is thus decoupled from "the two TE picture signals simultaneously propagated in opposite directions thru the generally circular waveguide 10.' Y

Figs. 3, 4 and 5 show a modified form of the invention" wherein the corresponding parts bear the same nurnerals as that used in Figs. 1 and 2 except that prime designations are added. The generally circular waveguide 10' has a square cross-section, and the main waveguide 13' of the magic T is formed in an angular configuration. The form of the invention shown in Figs. 3,-'4 and 5 also ditfers from the form already described asound-signal to the antenna array.

in that the generally circular waveguide 10' includes an --inner coaxial conductor 25 having a tapered end 26 in the tapered portion 11'.

As shown to advantage in Fig. 4, the probes 16' and 17"connect directly to the inner conductor 25. The two TE modes in the generally circular waveguide 10' coupled from the picture input waveguide 12 and coupled to the reflected signal output waveguide 14' are essentially unaflEected by the presence of the inner conductor 25 and its tapered end 26. The sound signal applied thru the waveguide 15' and the main waveguide 13' of the magic T to the probes 16 and 17 excites theTEM or coaxialline' mode in the generally circular waveguide 10'. This energy is then conveyed or propagated in the coaxial line mode to the antenna.

Figs. 3 and 5 also illustrate a construction including a baflle 28 extending in a plane and connecting the tapered end 26 of the inner conductor to the opposite parallel sidewalls of the tapered portion 11'. The baffie 28 lies in the equi-potential plane for the TE mode propagated thru the tapered portion 11' from the rectangular waveguide 12. The baffle 28 therefore has no effect on the propagation ofthe picture signal from the transmitter to the antenna array. The baffle 28, however, serves to produce a short circuit for the reflected TE mode and to the TM mode at a location with respect to the probes 16 and 17- favorable from a bandwidth viewpoint. Furthermore, the baffle reduces the cross-coupling between the waveguide 12 and the waveguide 13.

It will be understood that the form of the invention shown in Figs. 1 and 2 may 'be modified for the propagation thru the generally circular waveguide 10 of a coaxial line mode byincorporating the construction shown in Figs. 3 thru- 5 including a coaxial inner conductor 25 having a tapered end 26, probes 16' and 17 connected to the inner conductor 25, and a baffle plate 28. The TEM or coaxial line mode is employed for the propagation of -By the use of the coaxial line mode for this purpose, the waveguide system is useful over a broader range of frequencies. This is due to the fact that the coaxial line mode has no lower cut-off frequency, whereas the TM mode has a fairly high lower cut-ofl? frequency. A waveguide system operative over a broad range of frequencies is of considerable commercial importance when, for example, it is desired to build a system for television broadcasting in such a way that a structure of a given size may be used forany one of the considerable number of television channel frequencies.

a It will be understod that the invention is useful in applications other than television broadcasting and that it may be utilized for energy flow in either direction be-' tween the generally circular waveguide and each of the rectangular waveguides. What is claimed is: Y

1. Means to provide separate couplings for each of three decoupled signals in a single waveguide, comprising, a generally circular waveguide, a rectangular waveguide having one cross-sectional dimension smaller thanv the cross-sectional dimension of said generally circular waveguide, a waveguide transition connecting one end of said generally circular waveguide to one end of said rectangular waveguide, a magic T having a main wave guide, an 'E-plane arm and an H-plane arm connected together ata junction, said main waveguide being formed around said'generally circular waveguide, and means coupling energy from saidv main waveguide at points equi-distant from said junction to points on opposite sides of said generally circular waveguide.

2. The combination as defined in claim 1 wherein said H-plane arm of said magic T is arranged in parallel spaced relation with said rectangular waveguide, the plane of the larger sidewall of one being parallel with the plane of the larger sidewall of the other.

3. The combination as defined in claim 1, and in addi- Ltion, a coaxial inner conductor extending longitudinally in said generally circular waveguide and having a tapered end in said transformer.

4. The combination as defined in claim 1 wherein said means for coupling energy from said main waveguide to said generally circular waveguide comprises probes extending from said main waveguide thru apertures into said generally circular waveguide.

5. The combination as defined in claim 4, and in addition, a coaxial inner conductor extending longitudinally in said generally circular waveguide and having a tapered end in said transformer, said probes extending to and making contact with said inner conductor.

6. The combination as defined in claim 5, and in addition, a bafiie plate extending in a plane in both directions from said tapered end of the inner conductor to opposite sidewalls of said transformer.

7. A broadband high-power waveguide system for coupling the output of a television picture transmitter and the output of a television sound transmitter to a single antenna, comprising, a generally circular waveguide adapted at one endfor coupling to a transmitting antenna, a rectangular waveguide having one cross-sectional dimension smaller than the cross-sectional dimension of said generally circular waveguide, a tapered portion connecting the other end of said generally circular wave guide to one end of said rectangular waveguide, a magic T having a main waveguide, an E-plane arm and an H-plane arm connected together at a junction, said main waveguide being formed around said generally circular waveguide, a coaxial inner conductor in said generally circular waveguide, and means coupling energy from said main waveguide at points equi-distant from said junction to points symmetrically disposed in said generally circular waveguide.

8. A waveguide system as defined in claim 7 wherein said coupling means comprise transverse conductors axially aligned with each other and extending from said inner conductor thru apertures in said generally circular waveguide on opposite sides thereof to sidewalls of said main waveguide.

9. A diplexer for combining two decoupled signals in a single waveguide, comprising, a generally circular waveguide, a first rectangular waveguide having one crosssectional dimension smaller than the cross-sectional dimension of said generally circular waveguide, a waveguide transition connecting one end of said generally circular waveguide to one end of said first rectangular waveguide, a second rectangular waveguide wrapped at least partially around said generally circular waveguide with the greater cross-sectional dimension parallel with the longitudinal axis of said generally circular waveguide,

a third rectangular waveguide connected to an intermediate junction point on said second rectangular waveguide, and means coupling energy from said second waveguide at points equi-distant from said junction point to opposite sides in said generally circular waveguide, whereby TE modes in said first and third rectangular Waveguides excite decoupled modes in said generally circular waveguide.

10. A diplexer for combining two decoupled signals in a single waveguide, comprising, a generally circular waveguide, a magic T having a main waveguide, an E-plane arm and an H-plane arm connected together at a junction, said main waveguide being formed around said generally circular waveguide, and means coupling energy from said main waveguide at points equi-distant from said junction to points on opposite sides in said generally circular waveguide, whereby TE modes in said E-plane and H-plane arms excite decoupled modes in said generally circular waveguide.

11. A diplexer for combining two decoupled signals in a single waveguide, comprising a generally circular waveguide, a first rectangular waveguide, a waveguide transition connecting one end of said generally circular waveguide to one end of said first rectangular waveguide, a second rectangular waveguide wrapped at least partially around said generally circular waveguide, means for shortcircuiting the ends of said second rectangular waveguide, a third rectangular waveguide connected to said second rectangular waveguide at a point substantially equidistant from said ends of said second rectangular waveguide, and means coupling energy from said second rectangular waveguide at points substantially equidistant from said ends of said second rectangular waveguide to opposite sides in said generally circular waveguide.

O. G. June 10. 1952. PP. 659.

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