US2471021A - Radio wave guide - Google Patents

Description

May 24, 1949.

w. E. BRADLEY 2,471,021

RADIO WAVE GUIDE Original Filed Aug. 15 1944 2 Sheets-Sheet 1 WILLIAM E. BRADLEY ATTORNEY INVENTOR. 53

May 24, 1949. E, BRADLEY 2,471,021

RADIO WAVE 'GUIDE 2 Sheets-Sheet 2.

Original Filed Aug. 15, 1944 FIG.5

FIGJO.

INVENTOR." WILLIAM E. BRADLEY BY ATTORNEY Patented May 24, 1949 *mesne assignments, to Philco Corporation, Philadelphia, Pa, a corporation of Pennsylvania Original application August 15, 1944, Serial No. 549,618. Divided and this application August 31, 1944, Serial No. 552,174

11 Claims. 1.,

application is 'a division -ofmy application Serial No. 549,618; filed August 1 5', 1944, now abandoned, and relates in general tothe fields of ultra-high frequency signal transmission and more particularly con'cerns'hovel means for gen erating particular modes of wave transmission.

In micro-wave transmission in wave guides and in various other applications; it is often desirable to transmit a single oscillation mode. For example, for transmission over a considerable distance, it is well known that the 'I'Eor mode of propagation is that which involves the lowest attenuation loss.

Moreover, for certain directional antenna structures, it is desirable todrive with a-particular oscillation mode in order to obtain the required directional characteristic, as for example a horizontally polarized energy distribution pattern omnidirectional in the horizontal plane. antenna array comprising a plurality of stacked biconical horns upon a slotted cavity resonator gives an excellent horizontal polarization act'eristic 'of high directivity. The antenna-structure is simpler and has lower loss than the conventi'onal stacked di-pole array and is better adaptedto operation on: ultra high frequencies. It. therefore has considerable application in micro-wave transmission.

However, in order to -obtain auniform circular energy distribution from the stacked biconica'l' horn antenna, it has been found that excitation must be accomplished by the TEOl mode of oscillation. Should other modes enter the drivin cavity towards this positive antenna, the field distribution pattern ate. distance from the antenna will no longer be quite circular, -but will have pronounced symmetrical lobes, the number of which will be determined by the nature of the spurious oscillation modes. For example, it has been found that attempts to excite a 'TEor-oscillation mode have been accompanied by the generationof a considerable TE21 mode in a circular pipe.

Since the T1321 oscillation can exist in'a smaller diameter pipe than the Thin, it is ordinarily difficult to remove this spurious mode. In the stacked biconical horn antenna structure, the TE21 wave Will result in a pronounced four-way symmetry over the circular horizontal field distribution obtained by the TEM wave alone.

In the past, attempts togenerate the low'a'ttenuation TEm oscillation mode have been accomplis'hed by complex driving apparatus and have resulted in an inpure wave, including several other oscillation-modes.

It has thus become thepractice to attempt to resonate the antenna struts-- tu-re whenever possible for the 'IEor wave order that maximum power output at this modecould be obtained.

My. invention contemplates a wave guide transmission system including a number of transducers permitting the excitation in one central cavity of the T1301 wave in its pure state.

In order to excite the 'IEo1 mode in a circular wave guide, my invention contemplates the use of a driving network which couples into the circular wave guide through symmetrically-arranged slots, excited to an equal extent in the same time phase with respect to the circular wave of the TEM mode and in the same sense. Feeding energyinto the wave guide through aslot prevents any longitudinalfield and thus prevents coupling tomodes having longitudinal patterns.

such phase as to excite the 'IEoi mode.

'IEzr mode.

It is therefore an object "of my invention. to

provide means vfor generating the 'I'Eor wave in.

its pure state.

Another object of .my invention: is to: provide transducers for coupling an oscillating:sourceto a wave guide or thelike which-will transmit only the T-Eor oscillation mode.

A further object of my invention isv-toxprovidea a means for coupling a rectangular Waveguideto a hollow circular waveguide in such 'a manner that the transmitted wave excited intheiguideis essentially the 'TEor mode.

Another objectof my invention i z t'oigenerate the TEm oscillation mode in pure form in a onciilar wave guide.

Still another object of my invention is to utilize a novel arrangement of symmetrical slits in an end plate of a Wave guide resulting in the genera'tion of a 'IEm wave.

These and other objects of my invention will now become apparent from the-following sp'ecii'ication taken in connection with the accompanying drawings in-which:

'Figure l is a general diagrammaticrepresentation 'ofa stack biconical horn antenna structure coupled to a wave guide in which the "'IEbr wave is excited.

Figure 2 is a front view of one system-for excitinga 'TEti wave in a'circular wave guide.

Figure 3 is a top View of the Wave guide structure illustrated in Figure 2.

Figure 4 is a perspective view of the wave guide structure illustrated in Figures 2 and 3.

Figure 5 is a perspective of a wave guide show ing the T1311 mode.

Figure 6 is an end view showing the transverse mode TEn.

Figure '7 is a perspective of a wave guide with a 'IMoi mode.

Figure 8 is a longitudinal section of Figure 7.

Figure 9 is a cross-section of a wave guide showing the TE21 mode.

Figure 10 is an elongated section of Figure 9.

Figure 11 is a cross-section of a wave guide showing a TEUI mode.

Figure 12 is an illustration of the field distribution at slits in a plate.

In Figure 1, there is illustrated an antenna structure which presents certain decided advantages when driven by a TE-n signal. This antenna structure comprising essentially a stacked biconical horn array is commonly utilized to develop a field distribution having a uniform circular horizontal pattern. That is to say, the signal strength radiated from the structure illustrated in Figure 1 when excited by the TE-n wave is independent of azimuth.

Basically, the antenna structure consists of a segmental cavity resonator 2!. This cavity resona'tor comprises essentially a length of wave guide which is closed at the lower end by an adjustable metallic plate 53, and at the upper end by a movable piston-type plate 23. The movable closure 23 is utilized to resonate the cavity 2i at the desired frequency.

Extending from the outer wall of the cavity resonator iii are a plurality of plates 24, alternate ones being inverted, and in contact with each other as illustrated by the plates 25 and 26. cavity resonator 2! is excited as illustrated by energy fed over a hollow wave guide H2. The hollow wave guide H2 is, as will be more fully explained hereinafter, excited by the T301 mode only.

The coupling from the cavity for the biconical horns illustrated in Figure 1 is obtained by circumferentially slitting the cavity 2! as at 3!. The circular slits extend about the entire perimeter of the cavity between the stacked metallic plates as 25 and 23. The supporting means for maintaining the cavity segments such as 2! in the proper spaced relation are not illustrated but of course comprise conventional high frequency insulating means.

By the use of the single resonant cavity illustrated, it is possible by proper placement of the circumferential slits to obtain a highly intense field pattern in the horizontal plane.

The biconical stacked horn arrangement illustrated in Figure 1 is illustrative of an ultra-high frequency system which is best operative from a source of TEo1 electro-magnetic waves. Thus, with the use of TEoi waves in the cavity illustrated, the electric field is horizontal at all points and circular about the axis of the cavity. Accordingly, the field pattern radiated through the slits 3| and between the flared horn structure is essentially an intense horizontally polarized signal and has omnidirectional vertical activity. The circumferential slits such as 3! are placed in a location wher the waves radiating therefrom are in phase and form as intense a beam as is possible on the horizon. In the illustrated construction, the slits are shown of uniform width,

The.

although this need not always be the case. For example, in the three element structure shown, in order to further suppress side lobes, I prefer to make the center gap approximately fifteen per cent wider than the outer gaps, the latter being kept uniform.

This antenna structure which has lower loss and has far greater utility due to its simplicity than the stacked dipole array is dependent for proper operation upon the excitation of the TE01 waves in pure form in the cavity 2!. In the following description, various means will be illustrated embodying my invention for generating a TEOI wave. It is to be understood that the application of the transducers to be described is not necessarily limited to the biconical horn antenna disclosed in Figure l, but may be utilized wherever transmission of micro-wave for a considerable distance is required.

In order to more fully explain the operation of my novel transducers, a brief review of modes and structures for launching them will be given.

In Figures 5 to B, I show cavity modes in the order of their appearances as the frequency is raised. When the pipe is large enough to contain several modes, the modes which actually exist depend on the type of launcher.

The first mode that will appear is the TE'n, shown in Figure 5. As shown, the TEn is a transverse mode, the electric fields running from the top to the bottom of the pipe. Between points where there are large electric fields, there are nodal planes where the electric field vanishes. In the case of a traveling wave in the guide, this whole pattern is rushing along the guide and the pattern seems to move faster than the speed of light. In a cavity the pattern stands still, the electric field just reversing its phase at radio frequency. That is the first mode that appears. This mode obviously has polarization. It will appear with a polarization determined by the launcher and must be received in a suitable manner. A dipole would do for the launcher and receiver.

The next is a TMo mode shown in Figure 6. This mode shows no polarization. The electric field is shown by the arrows. It is conveniently excited by a launcher consisting of a simple quarter-wave antenna standing in the center along the axis.

The TE'21 shown in Figure '7 is the next mode. Like the 'IEn it is purely transverse, there being no longitudinal electric lines.

Figure 8 is the T5201. There are any number of them beyond these modes, but these will sufiice for the present discussion. In the TE01 mode, the electrical field nowhere touches a metal surface.

The Thin is obviously suitable for the radiation of horizontal polarization through a circumferential slot as shown in Figure l.

I have discovered that such a mode can be launched by opening a wave guide into a cavity through a symmetrical arrangement of slots. If, for example, two opposed slots are provided in the bottom of a wave guide fed from a suitable Wave guide, it is possible to drive the two slots exactly out of phase and the TEM mode whose electric field crosses both slots in the same sense is coupled into the wave guide. The TEn will not be excited since the Thin has a diametrical electric field across it. It will not couple to TMor because no net longitudinal electric field is set up.

With an orientation as shown by the two slots in solid lines in Figure 9, the TE21, however, will also-be excited; In this figure; the isshown dotted in the form in which it will becoupled. Ins the neighborhood of the slots, there will be electric fields which will be parallel to the electric field of the slots and the phase will be such as to-be excited by two slots which are driven with thesense of field shown by the solid arrows.

Figures 2to 4 are illustrative of a simple conveniently constructed transducer embodying the above principles in. which slots are excited symmetrically and. symmetrical branches of wave guides are provided for generating the TEoi transmission: mode in: a circular. wave guide. This is calledia gallery or two-way drive associated with a critical length tobalance out the TEZl mode.

Asillustrated, a circular hollow wave guide 4| is coupled near one end-thereof to a transducer 42: compr-ising essentially a rectangular wave-guide extending from the source of high frequency energy; The hollow wave guide 4| may be coupled? to whatever system is being driven by the ultra-high frequency energy, such as the cavity of. the biconical horns of Figure 1.

At: junction point 43, the rectangular wave guide 42 is split. to form a T joint thereat. The two sections of wave guide. extending from the joint 43 are circularly bent as best illustrated in Figure 3. to straddle the circular wave guide 4-|= and form curved sections 44 and 45. The cross-section. of the. curved sections 44 and 45 is of. course rectangular similar to the main guide 42;.

The two circular extensions 44 and 45 of the rectangular. wave guide. 42. are plugged at 46 and 41, Figure 3, respectively, by rectangular plates. Atdiametrically opposed points and 52-, the cylindrical waveguide 4| and the wave guide extensions 44. and 45 are slotted as is best illustrated in Figure 2. These slots 5| and 52 are the electro-magnetic coupling openings between the rectangular guide 42 and the circular guide 4|.

Asis illustrated in Figure 3, the distance measured along. the circumference between the rectangular slot 52 and the metallic plug 41 is substantially equal to one-half the wave length in guide 45-. This condition is also true for the distance between the slot 5| and the metal plug 46.

By. adjustment of the position of the plug with respect. to the slot, the inductance due to the peculiar place of the slit in the guide is compensated out. When the location of these two little plugs are found,.they are soldered in place. The cross-sectional dimensions of these branch guides must be carefully chosen by determining what the input impedance of these two slots will be for theTEoi mode.

It will. now be apparent from the above that the'slots will have an induction field having the proper polarization or'sense of phase which will tend todrive the TEM- In other words, the slots will be excited in push-pull provided the lengths of. the branch guides 44 and 45 are equal.

This gallery type of drive will, however, also excitethe TE21 as already explained in connection' with Figure 9, although it will successfully avoid excitation of TEn and TMoi. To balance outthe TEZI it is efiectively short-circuited. This is effected by sealing one end'of: the circular Wave guide 4| by an adjustable circular metal plate 53 as shown in Figure 4. By appropriately determining; the. length between the rectangular slots SI.- and: 52' and the metal plate 53, the TE21 mode of-oscillation may be. completely suppressed within the circular wave guide- 4|. That is to say, by'properly choosing the aforementionerf (1151' tance, the: energy oi-"tliissv undesiredr'm'm dscill.

lation mode which enterstiromi thez rectangular: guide 42- may becompletelw balanced out. This:

distance is: somewhat: critical: andz-ris'a arr integral 1 number of halfwavelengthswi the". TE21. mode;

as measured from theefl'ectiveacenten otrl slots 5 if and-52'.

The drive mechanisnrillustrated' is :suchz as}. to permit only: the desired 'IEdr. oscillation: mode to: exist within: the circul'an waveaguide; 4|. As is. well known, this particularr mode will. be;-trans+- mitted' down the guide: withi mi'nimumza. attenua. tion. For the particular; transducer illustrated in Figures 2 to 4', the two-away symmetry provided by the rectangular. slots? 5| and. 52 permit the transmission of: the: 'IEorwave: and the metal.

plate 53 results in the balancing out of. undei-- sired oscillation modes:

The principle of operation of: the transducer.

illustrated in Figures 2 andiBumay be summarized. by the general. statement that thecircular Wave guide is energized from a transducer comprising two diametrically opposite slots having two-way symmetry in the circumferential. or angular dimension. The TEoiand TEfn are, as. will now be clear,- produced. The'I'Ezr mode" is suppressed: by sealing one end of the guide at a critical; distance from'the slots;

To excite the TEor mode, there=mustbe produced at-each slot an equal-"component ofielectromotive force in the samephase andin a circumferential direction. 'I'hel'ength of the guide from the point of junctions-to the slots must be such that both slots are drivenequally. This maybe done bythe gallery arrangement here:

illustrated or in any other construction which will effect such equal drives of the two slots.

It will now be clear that-thiswave guidein which a pure-TEor Wavehasbeen generated, maybe coupled to the resonant cavity 2| of the stacked horn antenna array and a horizontally polarized wave is thusdeveloped.

The circular wave guide 62, as already stated, is chosen such that its diameter is greater than-- that required totransmit the-TE'oi mode. However, this diameter is small'erthanthat required for transmission of the next higher mode.

If, however; it is desired totransmit this energy in a larger diameter pipe, and accordingly minimize attenuation, a flared fitting l l (Figure 1)- may be used' as a coupler between wave guide section 62 and larger" diameter circular wave guides 2 directly coupled in the illustration here to the cavity of the conical horn antenna.

As the TEZl mode is completely suppressed as As this oscillation mode is transmitted with minimum attenuation, it is clear'that transmission of high frequency energy-over considerabledistances as, for example, inter-city communication, may bebest accomplishedby this arrangement, the wave guide of which may be of the ond circular wave guide, said first wave guide having two branches extending on opposite-sides" of said second wave guide, a symmetrical arrangement of slots diametrically opposed in said second circular wave guide, a symmetrical arrangement of slots diametrically opposed in said first wave guide and in juxtaposed relation with said first mentioned slots in said circular wave guide for providing a coupling between said second circular Wave guide and said first wave guide, means for driving said slots from the first wave guide in the same time phase with respect to the TE01 mode and in the same phase for exciting the TEM mode in said second wave guide.

2. In a high frequency system, a first rectangular wave guide conducting high frequency energy, a second circular wave guide, said first wave guide having two branches extending on opposed sides of said second circular wave guide, a symmetrical arrangement of slots in the walls of said second circular wave guide adjacent to the walls of said first wave guide, a symmetrical arrangement of slots in the walls of said first wave guide adjacent to the walls of said second wave guide, said slots being juxtaposed with respect to each other for coupling said second wave guide to said first wave guide, means for exciting said slots in said first wave guide equally in such phase as to excite the TEOl and IE-21 modes in said second wave guide, and means within the second wave guide for balancing out the T1321 mode.

3. In a high frequency system, a first rectangular wave guide conducting high frequency energy, a second circular wave guide, said first wave guide having two branches extending on opposed sides of said second wave guide, a symmetrical arrangement of slots in the walls of said first wave guide adjacent the walls of said second wave guide, a symmetrical arrangement of slots in the walls of said second wave guide adjacent the walls of said first wave guide, said slots in said first wave guide being juxtaposed to the slots in said second wave guide for coupling said second wave guide to said first wave guide, said slots being in diametrically opposed relation with respect to each other, and means for exciting said slots in said first wave guide equally and in such phase as to excite the TEM mode in said second wave guide.

4. a high frequency system, a first rectangular wave guide conducting high frequency energy, a second circular wave gide, said first wave guide having two branches extending on opposed sides of said second wave guide, a symmetrical arrangement of slots in the walls of said first Wave guide adjacent the walls of said second wave guide, a symmetrical arrangement of slots in the walls of said second wave guide adjacent the walls of said first wave guide, said slots being juxtaposed with respect to each other for couplin said second wave guide to said first wave guide, means for driving said slots from the first wave guide in the same time phase with respect to the TEM mode in said second wave guide, and means within the second wave guide for balancing out the TE21 mode.

5. In a high frequency system, a rectangular wave guide conducting high frequency energy, a second Wave guide, a third wave guide having two branches, said rectangular Wave guide being joined to said third wave guide at the junction of the two branches, the branches extending to opposite sides of said second wave guide and slots formed in said two wave guide branches, and said second wave guide in diametrically opposed relation with respect to each other, said slots of said two wave guide branches being juxtaposed to the corresponding slots of the second wave guide, said slots being symmetrically arranged to receive equal and in phase energy from said rectangular wave guide.

6. In a hi h frequency system, a rectangular wave guide conducting high frequency energy, a second wave guide, a third Wave guide having two branches, said rectangular wave guide being joined to said third wave guide at the junction of the branches, the branches extending to opposite sides of said second wave guide and slots formed in said two wave guide branches, and said second wave guide, said slots of said two wave guide branches being juxtaposed to the corresponding slots of the second Wave guide, said slots being symmetrically arranged to receive equal ener y from said rectangular wave guide, and a closure for said second wave guide at a critical distance from said slots for balancing out the TElzi mode.

7. In a high frequency system, a rectangular wave guide conducting high frequency energy, a second wave guide, a third wave guide having two branches, said rectangular wave guide being joined to the third wave guide at the junction of the two branches, the branches extending to opposite sides of said second wave guide and slots formed in said two Wave guide branches and said second wave guide, said slots of said two wave guide branch-es being juxtaposed to the corresponding slots of the second wave guide, said slots being symmetrically arranged to receive equal energy from said rectangular wave guide, said wave guide branches being closed at their ends at a distance to the slots formed therein substantially equal to one half wave length.

8. In a high frequency system, a rectangular Wave guide conducting high frequency energy, a second Wave guide, a third wave guide having two branches, said rectangular wave guide being joined to the third wave guide at the junction of the branches, the branches extending to opposite sides of said second wave guide and slots formed in said two Wave guide branches and said second wave guide, said slots of said two wave guide branches being juxtaposed to the corresponding slots of the second wave guide, said slots being symmetrically arranged to receive equal energy from said rectangular wave guide, the cross-sectional dimensions of said wave guide branches being determined by the input impedance of the slots for the 'IEor mode.

9. In a high frequency system, a rectangular wave guide conducting high frequency energy, a second Wave guide, a third wave guide having two branches, said rectangular wave guide being joined to the third wave guide at the junction of the branches, the branches extending to opposite sides of said second wave guide and slots formed in said two wave guide branches and said second wave guide, said slots of said two wave guide branches being juxtaposed to the corresponding slots of the second wave guide, said slots being symmetrically arranged to receive equal energy from said rectangular Wave guide, and a closure for said second Wave guide placed from the effective center of said slots, a distance determined by an integral number of half wave lengths of the TE21 mode.

10. In a high frequency system, a rectangular wave guide conducting high frequency energy; a circular wave guide having diametrically opposed slots, and a transducer extending from said rectangular to said circular wave guide for coupling said wave guides, said transducer comprisll'lg two diametrically opposite slots juxtaposed to said slots in said circular wave guide having two way axial symmetry in the circular dimension.

11. In a high frequency system, a rectangular wave guide conducting high frequency energy; a circular wave guide having diametrically opposed slots, and a transducer extending from said rectangular to said circular wave guide for coupling said wave guides, said transducer comprising two diametrically opposite slots juxtaposed to said slots in said circular Wave guide having two Way axial symmetry in the circular dimension, said circular wave guide being closed at one end at a critical distance from said slots for suppressing the TE21 mode.

WILLIAM E. BRADLEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,129,669 Bowen Sept. 13, 1938 2,206,923 Southworth July 9, 1940 2,241,119 Dallenbach May 6, 1941 10 2,401,751 Friis June 11, 1946 FOREIGN PATENTS Number Country Date 417,564 Great Britain Sept. 29, 1934

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