US2818566A

US2818566A - Center-fed waveguide antenna

Info

Publication number: US2818566A
Application number: US469695A
Authority: US
Inventors: Rankin John Bruce
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1954-11-18
Filing date: 1954-11-18
Publication date: 1957-12-31
Anticipated expiration: 1974-12-31

Description

Dec. 31, 1957 i J. B. RANKIIQ 2,818,566

CENTER-FED WAVEGUIDE ANTENNA Filed Nov. 18, 1954 v 2 Sheets-Sheet 2 INVENTORY JOHN B. RANKIN waveguide.

22,818,555 CENTER-'FEDYWAVEGUIDEANTENNA John Bruce Rankin, skillmaneNfiL a'ssi'gnor toRadio Corporation of America, a corporation of Delaware The invention relates to antennas. and particularly to ahighgain, omnidirectional, center-fed waveguide antenna capable of handlinghighpowerfor iiltra highfrequency broadcasting, and thefeeding system therefor.

Antenna arrays for transmitting ultrahigh frequency signalshave been devised which consist of radiating elements equally spaced about the circumference of a cylindrical waveguide. 'In the utilization of *such an antenna array, .forexample, in television broadcasting, picture and sound energy travel-from one end of the antenna .array along the length of the antenna to diiferent radiating layers. One disadvantage of 'suchan end fed antenna system is that the radiated beam will tilt vertically with frequency. A center-fed antenna maybe :used to remove this unwanted tilting of the transmitted signal.

In-a center-fed antenna used for television broadcasting, both the picture and accompanyingjsound signal 'may'be diplexed into the same antenna by a hollow pipe waveguide or a transmission line arrangement from'a part of the feed system for the antenna .withoutthe rnecessity for separate frequency selective ,filters. Antennas for television broadcasting which utilize coaxial and other wave transmissionlines in this type of antenna '.feeding system are limited with respectto theirpower handling capabilities. This invention utilizes pipe wave guides. of large dimensions throughout .its construction "because of the attendant higher power handling capabilities.

An object of the invention islto obtain an improved center-fed antenna for ultra highfrequency transmission utilizing pipe waveguides of large dimension'throug'hout.

Another object is to obtain'the centerfeeding of, signals from a single hollowpi'pe waveguide a single surrounding coaxial waveguide whichexc'ites a plurality of antenna elements.

Theinventionmakes useof a center-fed antenna system comprising a rectangular waveguide 'into which or from which is fed an ultra-high frequency signal. The rectangular waveguide 'is secured at'the free end to a circular,'hollowwave'guide by means .of a tapered circular to-rectangular coupling means or transition. .A section of a second rectangular waveguide is positioned at right angles to the first identified rectangular waveguide and secured to the circular waveguide. An absorbing resistor serves to terminate the second identified rectangular waveguide. I V

The antenna array includes the above-mentioned circular, hollow waveguide or "inner waveguide to which is connected at one end'by meanso'f the tapered transition the first identified rectangular waveguide, whereby energy maybe fed to or taken from .the circular waveguide. A

.second circular or outer'waveguideis positioned so .that

substantially one-halfof its total surface area surrounds the-effective portion of the first mentioned circular, hollow A plurality of radiating elements in-layers are equally spaced abouttlre circumference.oftthesecond or outer circular waveguide. Coupling .Pl'ObfiS PDSiii-Ollfid adjacent to the end ofthe first mentioned circular wave- 2,818,566 Ratented Dec. 31, 1957 "ice guide serve to transfer energy from the inner waveguide will be capable of handling high power.

A more detailed description follows in conjunction with the accompanying drawingin which like reference numerals refer tolike parts throughout the figures of the drawing and in which:

Fig. 1 is a diagrammatical view of an omnidirectional antennalarray in accordance with the invention and the feeding system therefor;

Fig. 2 is an enlarged elevation of the antenna array" 1 shown in Fig. 1;

Fig. 3 .is a view of a layer of radiating elements of the antenna array taken immediately below line 3-3 of Fig. 2;

Fig. 4 is a view of the layer of coupling probes between the waveguides of the antenna array taken immediately "below line 44'of Fig. 2;

Fig. 5 is a perspective view of a section of the antenna feeding system shown in Fig. 1 including the rectangular- .to-circu'lar waveguide transition.

Fig. ,6 isa plan view of the section of the antenna feeding system shown in Fig. 5.

Referring to Figs. 1 and 2, an antenna array 1 which may be mounted as a tower or fastened to a suitable support, not shown, includes a cylinder 2. A metallic short- .circuiting plug 5 is positioned in the cylinder 2 at a distance removed from one end thereof. A second cylinder 3 of greater diameter than that of cylinder 2 is mounted so as to surround the cylinder 2, approximately one-half of the total surface area of the cylinder 3 being located below the'short-circuiting plug 5. An antenna array consisting of two pipe waveguides has been constructed. The portion of cylinder 2 terminated by plug 5 constitutes one waveguide .9, the outer surface of cylinder 2 and cylinder 3 forming a second coaxial waveguide 6. Coupling probes 4 are mounted so as to pass through the wall of the inner waveguide 9 in proximity to the short-circuiting plug 5 and serve to couple energy traveling in the inner waveguide9 to the center of the outer waveguide 6. A number of radiator probes in the form of unipoles 10 are arranged in layers and are equally spaced circumferentially about the surface of the array 1. The ends of .the outer waveguide 6 are terminated by short-circuitingiplugs 7 and 8, the positions of which are adjustable. Energy traveling in the inner waveguide 9 will be coupled to the center of the outer waveguide 6. The energy so coupled will then travel up and down the waveguide 6 to the shortclrcuiting plugs 7 and 8, respectively. The energy in the waveguide 6 will be coupled from the waveguide to free space by the radiator probes 10 positioned about the surface of the array 1.

By making the short-circuiting plug 5 adjustable, it may be used for the matching of the antenna array by altering its position in the waveguide 9 above coupling probes 4, as well as for preventing energy from continuing on in the waveguide 9 beyond plug 5.

The arrangement of radiator probes 10 may be .more clearly understood by an examination of Fig. 3 showing a view of the probes 10 of the array 1 taken immediately below line 33 of Fig. 2. Each layer of the array comprises eight probes 10 in the form of 'unipoles :equally individualbrass bushing 20 and insulatedfrom cylinder 3 by an insulator 21 which may be made of a polytetrafiuorethylene material marketed under the trade name Teflon.

The arrangement of coupling probes may be more clearly understood by an examination of Fig. 4 which shows a view of the probes 4 of the array 1 taken immediately below line 44 of Fig. 2. Eight probes 4 are equally spaced circumferentially about the surface of the array 1, the ends thereof extending into waveguide 9 at substantially right angles to the longitudinal axis thereof. The probes 4 are slidably secured to the cylinder 3 by brass bushings 23 and insulated from cylinder 2 by insulator 22 which may be of the same material as used to insulate the radiator probes it) from cylinder 3. The energy traveling in hollow waveguide 9 will be coupled to coaxial waveguide 6 by the proper insertion of the probes 4 into the waveguide 9. While the coupling probes 4 are positioned between the ends of waveguide 9, the exact position thereof in relation to that of the shortcircuiting plug 5 will be determined in accordance with the tuning and matching requirements of the arrangement which are brought about in part by the adjustment of plug 5. By providing a plurality of coupling probes, the power handled by each probe is a fraction of total power. Adequate means for coupling the energy between waveguides thus is obtained and satisfactory operation of the arrangement is insured.

The antenna array disclosed, due to the use of large pipe waveguides throughout is able to transmit signals of high power and of high gain. It is particularly suitable when used in the transmission of ultra-high frequency television broadcasting signals. Such an arrangement is shown in Fig. 1. A picture signal from a source, shown for purposes of illustration as rectangle 24, is con nected to a bridge network by a coaxial conductor 26. A source of sound signals, shown for purposes of illustration as rectangle 27, is connected to the bridge network 25 by a coaxial conductor 28.

The bridge network 25 utilized serves to combine the picture and sound signals coupled thereto into a common output and many various types suitable for use herein are well known in the art. For example, a iilterplexer may be used. The filterplexer performs the two functions of combining picture and sound and serving as the sideband filter for the picture transmitter. The output of the bridge network 25 is a rectangular waveguide 29.

At the base of the antenna array 1 is a network for connecting the rectangular waveguide 29 and another rectangular waveguide 36 to the common circular wave guide 9. Energy from the rectangular waveguides will be coupled into the circular waveguide 9 as, for example, linearly polarized TE modes, the two modes oriented at 90 with respect to each other. A commonly used network for this purpose includes a tapered transition 31 from rectangular waveguide 29 to circular waveguide 9. The second rectangular waveguide 30 is brought into the side of the circular waveguide 9 so that its broad faces are parallel to the axis of the circular waveguide 9 and perpendicular to the broad faces of the first rectangular waveguide 29. The angular length of the tapered transition 31 is chosen so that when a matched load is connected to the circular waveguide 9, the rectangular waveguide 30 looking in toward the junction of waveguides will be matched. A matched absorbing resistor 32 serves to terminate the rectangular waveguide 30. The circular, hollow waveguide 9 becomes the inner waveguide of the antenna.

Referring to Figs. 5 and 6, showing views of a section of the antenna feeding system shown in Fig. 1, a circular polarizer is positioned between the tapered transition 31 and the central coupling probes 4 of the antenna array 1. A simple form of matched circular polarizer consists of a pair of

axial fins

33 and 3 attached to the inside of the circular waveguide 9 and spaced one hundred and eighty degrees apart. A plane passing through both fins should be inclined 45 with respect to the surfaces of the rectangular waveguide 29. It is to be noted that the

fins

33 and 34 have not been shown in Fig. 1 because they are not in the plane of the drawing. The fins will cause the TE mode containing picture and sound signals to be circularly polarized. If a signal were fed from rectangular waveguide 30, the fins would cause the resulting TE mode in the circular waveguide 9 to be circularly polarized with opposite rotation.

The eight equally spaced probes 4 at the center of waveguide 6 and adjacent to the end of waveguide 9 transfer the energy from the inner circular, hollow waveguide 9 to the outer coaxial waveguide 6 formed by the outer surface of the inner waveguide 9 and cylinder 3. In the inner circular waveguide 9, energy which is reflected by the probes 4 travels back down the guide as a counterrotating circularly polarized TE mode. The fins reconvert the mode to linearly polarized TE mode oriented at with respect to the original signal. This reflected energy then feeds into the side rectangular waveguide 30 and is absorbed by the resistor 32.

An antenna array and feeding system therefor has been disclosed for successfully transmitting an ultra-high frequency television broadband signal of high power. Pipe waveguides are used as transmission lines throughout. The picture and sound energy fed to the inner waveguide 9 as a circularly polarized TE mode is coupled to the outer waveguide 6 by the probes 4. It is to be noted that no mode conversion will take place at this location. The energy coupled into the outer waveguide 6 will travel up and down the waveguide as a counter-rotating circularly poralized TE mode. The energy will thereafter be coupled tofree space by the radiator probes 10 which are tuned so as to be excited by the energy traveling in waveguide 6.

The proper tuning and matching of the antenna array may be accomplished by altering mechanically the position of several of the components thereof. The location of short-circuiting plug 5 may be altered to allow the proper coupling between the two

waveguides

9 and 6 by coupling probes 4. The coupling probes themselves are variable and may be slidably positioned to provide the proper tuning and matching. The extent of insertion of the ends of probes 4 into waveguide 9 will determine the amount of energy abstracted from waveguide 9. The radiator probes 10 are also slidably adjustable and may be used to vary the tuning and matching of the array. Shortcircuiting plugs 7 and 8 are adjustably positioned at the ends of coaxial waveguide 6 to aid in the proper matching of the radiator probes. A further means of control is in the selection of ratio of the cylinder diameters which is a variable and may be used to control the coaxial guide impedance.

An actual embodiment of the invention constructed to operate on a frequency range in the area of 800 me. would have the following electrical and physical dimensions. The wavelength of the signal in free space would be 14% (inches). It would be 24%," in the inner waveguide 9 and 15.9 in the outer waveguide 6.

The outer diameter of the cylinder 3 would be 14%.", the inner diameter thereof being 14". The outer diameter of the cylinder 2 would be 11", the inner diameter thereof being 10%". The distance between the longitudinal axis of each one of the coupling probes 4 and the bottom of the plug 5 would be or 18 measured in the waveguide 9. The distance' between the same longitudinal axis of the coupling probes 4 and the longitudinal axis of the adjacent radiator probes 10 would be %)r or 11.9 as measured in waveguide 6. The radiator probes 10 extending along the aperture of the antenna on each side of the coupling probes 4 would be one wavelength in the outer waveguide 6 or 15.9" apart. The short-circuiting plugs 7' and 8 would be positioned M4 in the outer waveguide 6 or '4" removed from the longitudinal axis of the end radiator probes 10. The length of the radiator probes will be approximately M4 or 3 The length of the coupling probes 4 will be of approximately the same value but, as in the case of the radiator probes 10, are slidably variable to allow for the proper tuning of the antenna array.

What is claimed is:

1. An antenna comprising a hollow waveguide, a second waveguide surrounding said first mentioned hollow waveguide, the outer surface of said first hollow waveguide constituting the inner surface of the second waveguide, circumferentially positioned probes extending into the said first mentioned waveguide at points removed from the end and at substantially right angles to the longitudinal axis thereof, said probes also extending into the said second waveguide substantially at the center thereof, a short-circuiting plug extending across said first waveguide at a point intermediate the ends of said second waveguide for preventing the flow of energy in said first waveguide therebeyond, energy traveling in said first waveguide being coupled to said second waveguide by said probes, and means for coupling said energy from said second waveguide to free space.

2. An antenna comprising a hollow pipe waveguide, a cylinder, said cylinder surrounding said hollow pipe waveguide, the outer surface of said hollow pipe waveguide constituting the inner surface of a coaxial waveguide in conjunction with said cylinder, circumferentially positioned probes extending into said hollow pipe waveguide at a point removed from the end and at substantially right angles to the longitudinal axis thereof, said probes also extending into said coaxial waveguide substantially at the center thereof, a short-circuiting plug extending across said hollow pipe waveguide intermediate the ends of said coaxial waveguide for preventing the flow of energy in said hollow pipe waveguide therebeyond, and means for coupling energy transferred from said hollow pipe waveguide to said coaxial waveguide by said probes to free space.

3. An antenna comprising a hollow pipe waveguide, a cylinder, said cylinder surrounding said hollow pipe waveguide, the outer surface of said hollow pipe waveguide and said cylinder forming a coaxial waveguide, short-circuiting plugs positioned at the open ends of said coaxial waveguide, a short-circuiting plug extending across said hollow pipe waveguide at a point intermediate the ends of said coaxial waveguide for preventing the flow of energy in said hollow pipe waveguide therebeyond, coupling probes secured to said cylinder and extending into said hollow pipe waveguide at a point removed from the end and at right angles to the longitudinal axis thereof, said probes being equally spaced circumferentially about the center of said coaxial waveguide, and means coexistent with said coaxial waveguide for coupling energy coupled to said coaxial waveguide from said hollow pipe waveguide by said probes to free space.

4. An antenna comprising a hollow pipe waveguide, a cylinder, said cylinder surrounding said hollow pipe waveguide, the outer surface of said hollow pipe waveguide and said cylinder forming a coaxial waveguide, a metallic short-circuiting plug mounted intermediate the ends of said coaxial waveguide in said hollow pipe waveguide, short-circuiting plugs mounted at the open ends of said coaxial waveguide, a layer of coupling probes secured to said cylinder wall and extending into said hollow pipe waveguide at a point removed from said first mentioned short-circuiting plug and at right angles to the longitudinal axis of said hollow pipe waveguide, said probes being equally spaced circumferentially about the center of said coaxial waveguide, a plurality of layers of radiator probes extending into free space at right angles to the surface of said coaxial waveguide, said radiator probes in each of said layers being equally spaced circumferentially about said antenna whereby energy coupled be- 6 tween said waveguides by said coupling probes is coupled to free space.

5. An antenna comprising a hollow pipe waveguide, a cylinder, said cylinder surrounding said hollow pipe waveguide, the outer surface of said hollow pipe waveguide and said cylinder forming a coaxial waveguide, a short-circuiting plug mounted intermediate the ends of said coaxial waveguide in said hollow pipe waveguide, short-circuiting plugs mounted at the open ends of said coaxial waveguide, a layer of coupling probes secured to said cylinder wall and extending into said hollow pipe waveguide at a point removed from said first mentioned short-circuiting plug and at right angles to the longitudinal axis of said hollow pipe waveguide, said probes being equally spaced circumferentially about the center of said coaxial waveguide, a plurality of layers of radiator probes extending into free space at right angles to the surface of said cylinder, said radiator probes being secured to the wall of said hollow pipe waveguide and passing through insulated apertures in the wall of said cylinder, the radiator probes in each of said layers being equally spaced circumferentially about said antenna whereby energy coupled between said waveguides by said coupling probes is coupled to free space.

6. An antenna comprising a hollow pipe waveguide, a cylinder, said cylinder surrounding said hollow pipe Waveguide, the outer surface of said hollow pipe waveguide and said cylinder forming a coaxial waveguide, a short-circuiting plug mounted intermediate the ends of said coaxial waveguide in said hollow pipe waveguide, short-circuiting plugs mounted at the open ends of said coaxial waveguide, a layer of coupling probes adjacent said first mentioned short-circuiting plug secured to said cylinder wall and extending into said hollow pipe waveguide at a point removed from the end and at right angles to the longitudinal axis of said hollow pipe waveguide, said probes being equally spaced circumferentially about the center of said coaxial waveguide, means for propagating energy of a circularly polarized TE mode in said hollow pipe waveguide, said energy being coupled to said coaxial waveguide by said coupling probes without mode conversion, a plurality of layers of radiator probes extending into free space at right angles to the surface of said cylinder, said radiator probes being secured to the wall of said hollow pipe waveguide and passing through insulated apertures in the wall of said cylinder, the radiator probes in each of said layers being equally spaced circumferentially about said antenna whereby energy coupled between said waveguides by said coupling probes is coupled to free space.

7. An antenna comprising a hollow waveguide, a second waveguide surrounding said first waveguide so that substantially one-half of the total surface area of said second waveguide surrounds said first waveguide, the outer surface of said first waveguide constituting the inner surface of said second waveguide, circumferentially positioned probes extending into said first waveguide at points removed from the end and at right angles to the longitudinal axis thereof, said probes also extending into said second waveguide at the center thereof, a short-circuiting plug extending across said first waveguide at a point intermediate the ends of said second waveguide for preventing the flow of energy in said first waveguide therebeyond, energy traveling in said first waveguide being coupled to said second waveguide by said probes, and means for radiating said energy from said second waveguide to free space.

References Cited in the file of this patent UNITED STATES PATENTS 2,408,435 Mason Oct. 1, 1946 2,658,143 Fiet et al. Nov. 3, 1953 2,705,305 Bailey Mar. 29, 1955