US2987721A - Broadband discage antenna - Google Patents

Description

June 1961 w. J. E. EDWARDS ETA]. 2,987,721

BROADBAND DISCAGE ANTENNA Filed Nov. 4, 1959 2 Sheets-Sheet 1 INVENTORB WILL/AM J.E. EDWARDS $14M E. PAR/(El? June 1961 w. J. E. EDWARDS ETAL 2,987,721

BROADBAND DISCAGE ANTENNA Filed Nov. 4, 1959 2 Sheets-Sheet 2 INVENTORS WILL IAM J. E. EDWARDS SAM E. PAR/(El? BY United States Patent 2,987,721 BROADBAND DISCAGE ANTENNA William J. E. Edwards, San Diego, and Sam E. Parker,

Pacific Palisades, Calif., assignors to the United States of America as represented by the Secretary of the Navy Filed Nov. 4, 1959, Ser. No. 850,977 2 Claims. (Cl. 343--725) (Granted under Title 35, U.'S. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for Governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates generally to communications antenna systems and in particular to broadband discage antennas having optimum radiation patterns consistent with selective low frequency, high frequency, and very high frequency operation. Even more particularly, the present invention concerns an antenna system consisting of a discone antenna which is combined structurally with a fat cage antenna in one compact, composite unit in such manner as to produce desirable impedance characteristics while using two or more driving points incorporated in appropriate mounting and feeding structure, although confined within a limited area or space such as would exist aboard ship.

With the ever increasing need for more communication channels in the high frequency band, a search for practical and functional broadband antennas which overcomes the limitations of narrowband antennas and which at the same time will provide desirable and usable radiation patterns is constantly in process. For example, antennas having small length-to-diameter ratios are already known to provide more nearly constant input impedance throughout a broad frequency band than those obtainable with so-called thin structures. In addition, it is also known to add one antenna to another and to decouple the combined elements thereof by means of frequency sensitive networks and transmission line stubs. However, although operable in a satisfactory manner for many purposes in an uncramped physical and electrical environment, it has been found that the existence of such environments are sometimes limited, which, in turn, limits their use to a considerable extent, inasmuch as broadband antennas are usually very large structures which naturally require more installation space than thin radiators. But even in desirable operating environments, it has been determined that the impedance and radiation characteristics of combined antennas are often changed and adversely affected by each other as well as by ambient external objects, due to the effective space-volume required to physically contain and position their coalescent structures.

This invention makes use of a simple but profound idea which is embodied in a structural device that involves the integration of two difierent but well known broadband antenna types into a single unitary device in such manner that the essential performance characteristics of each is retained without requiring substantially any more space than would be occupied by each antenna type taken separately.

The feasibility of combining a discone antenna and a cage antenna in one composite discage structure utilizing two feed points is substantiated by unusually good opera tional results, including improved impedance characteristics such that a voltage standing wave ratio of 3 to 1 or less is obtained over a frequency range of 6 to 1 when referred to a 50 ohm line. Moreover, in addition to individual antenna operation, the discage structure facilitates the handling of several communications channels simultaneously in, for example, the 5 to 30 mega base 23 which is constructed to improve the cage imped Patented June 6, 1961 cycle frequency range when multicoupling techniques are used in conjunction therewith, resulting in a reduction of the number of antennas needed which, in turn, should effect economies in construction and installation. Thus, it can be seen that the discage antenna systems constituting this invention are especially versatile and provides favorable impedance and radiation pattern characteristics over several octaves.

It is, therefore, a primary object of this invention to provide a communications antenna system having improved impedance and radiation pattern characteristics over a broad band of frequencies.

Another object of this invention is to combine a discone antenna and a cage antenna in a compact unit with a minimum of physical and electrical interference therebetween, regardless of whether each is used independently or whether both are used simultaneously.

A further object of this invention is to provide a broadband communications antenna system which requires substantially no more installation space than each would need separately.

Another object of this invention is to provide an antenna system with a 3 to 1 or less voltage standing wave ratio over a 6 to 1 operating frequency range.

Last, but not least, it is an object of this invention to provide a broadband communications system which is economical to construct and install.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof and wherein:

FIG. 1 is a perspective view showing the preferred embodiment of this invention shown schematically in part and structurally in part.

FIG. 2 is a perspective view of the invention with a modified feed system shown and a very high frequency antenna included.

Referring now to the drawings, there is shown in FIG. 1 a simulated disc antenna 11 containing a plurality of radiating conductors 12, each of which extends radially and horizontally from a center point 13. Coupled to radiating conductors 12 of said center point is an inner conductor 14 of a coaxial transmission line 15. An outer conductor 16 of said transmission line is so disposed as to simultaneously surround and contain said inner conductor and act as a support mast for the entire antenna assembly. Connected to the outer conductor of said transmission line is a cage antenna 17 containing a plurality of radiating conductors or wires 18 each of which is connected to external conductor 16 at an upper position 19 and a lower position 20 for electrical conductance therebetween. Said wires 18 extend outward and downward from upper position 19 to the outer extremity of support members 21 and then extend inward and downward therefrom toward the aforementioned lower position 20. Thus, it can be seen that wires 18 form a cagelike physical structure which, of course, produces a radiation pattern that depends upon the design parameters used in constructing same. Obviously, it is not intended that either the aforesaid disc or cage antennas be limited to the configurations herein disclosed, since the skilled artisan could readily design various and sundry angular and linear dimensions which would be suitable for producing desired structural forms and their inherently associated radiation patterns for any desired frequencies.

The base of support mast 16 is mounted on a floor surface 22 such as the deck of a ship or the like by means of an insulator type shunt feed system havinga mounting anceat the low frequency end of the operating range and to isolate the cage antenna from ground. The feed system contains a top cover 24 and a flange 25 which contains a plurality of bolt holes 26 for fastening it to said fioorsurface with bolts 27. Interposed between 'said cover and said flange is an upper insulator28 which providesiphysical support for the entire antenna array but prevents the grounding of same. The underside of said flange is connected to a lower insulator 28 whichextends through a hole in the floor surface, thus providing an insulated electrical path 'therethrough. The aforementioned cover, flange and insulators contain a hole along their assembled longitudinal axis whichaccommodates the lowerextension of mast 16. Inasmuch as mast 16 also acts as coaxial transmission line 15, said hole and transmission line accordingly constitute the foregoing electrical path. Mast "16 contains-threads 29 which cooperates with a 'nut 30*to hold it firmly in place after as .sembly of the mounting base. Alocknut 31 prevents loosening ofnut '30 due to vibration and, in addition, acts as a binding post foriconnecting a low frequency feed line '32 to the outer conductor of coaxial transmission line -15.

Attached to threads 29 at the lower extremity of mast 16 is an adapter 33 for changing therefrom to a coiled coaxial cable 34 of the RG8/U type or the equivalent. ThlS coaxial cable contains a plurality of coiled turns, depending on the frequency range of the antenna. The purpose ofthese coiled turns is toimprove the impedance characteristics of the high frequency antenna by providing a relatively high reactance thereat at the operating frequencies of the low frequency cage antenna and to isolate the low frequency antenna feed point from the high frequency antenna feed system.

Another species of the discage type antenna system constituting this invention is depicted in FIG. 2. The 'disc antenna and the cage antenna are shown to be in substantially comparable arrangement as the'discage an 'tenna of FIG. 1 and, therefore, provide similar impedance characteristics and radiation patterns. The distinguishing features, although small, facilitates the use of different mounting and feeding techniques and, moreover, may be used in conjunction with a very high frequency antenna without adding an exorbitant amount to the required installation space and without adversely affecting the operation of any one of the antennas of the entire array.

Referring now to FIG. 2, a disc antenna 35 is rigidly and electrically connected to an outer conductor 36 of a coaxial transmission mast 37. Mounted on said disc antenna is a very high frequency antenna 3-8 which is electrically coupled to an inner conductor 39 of said coaxial transmission mast. The position of the very high frequency is such that minimum interference exists between it and the disc and cage antennas during any predetermined operating conditions and consequently, it may be moved accordingly to accomplish such effect.

Coaxialtransmission mast 37 is rigidly mounted on a floor surface 40 such as the deck of a ship or the like. Mounting thereof may be achieved by any conventional means such as welding or bolting, as long as the attachment is sufficiently secure to prevent undue movement of the antenna array due to vibratory or turning motion of the aforementioned floor surface.

A cage antenna 41 surrounds said mast in a manner substantially similar to that illustrated in FIG. 1 but is insulated therefrom. The physical form may be somewhat different, though, depending on the design characteristics required to carry out desired operations. It is attached at the upper end to a wave stub bazooka transformer 42 which allows the disc antenna to be fed and still enables said mast to be grounded and mounted without an insulator and which, in addition, prevents the drive point of the disc and cage antennas from being' --2,9s7,7 21 A g short circuited by the feed cable of the aforesaid high r 4 7 frequency antenna or any other auxiliary antenna disposed on top of said disc antenna. It is attached at the bottom by a conductive ring 43 which, in turn, is held in suspension above said floor surface by the wires of the aforesaid cage antenna and insulator assemblies 44 connected to said floor surface through cables 45 Cage antenna 41 is fed a frequency of approximately 2 to 13 megacycles at ring 43 through a feed line 46 extending through a floor surface insulator "47 and an RG17 U-52 ohm coaxial cable '48.

Disc antenna 35 is fed approximately 13 to 30 megacycles through an RG17/U-52 ohm coaxial cable 49 having an outer conductor 50 connected to bazooka transformer 42 at' an aperture 51' in the side thereof and an inner conductor 52 extending through said aperture and coupled to outer conductor 36 of the aforementioned coaxial transmission mast 37 at a point electrically equal to 52 ohms resistance above the lower end of said transformer for impedance matching purposes.

A very high frequency of approximately 200 mega- .cycles may be fed to antenna '38 through the 52 ohm inner conductor 39 of said coaxial transmission mast, although it should be obvious that installation or use of the very high frequencyantenna is optional as far as operational characteristics of the other antennas of the discage array are concerned. Accordingly, it may be deleted from the entire assembly if so desired without adversely affecting impedance or radiation patterns thereof.

The operation of this invention is quite simple. Each of the antennas of the discage array is connected to its respective transmitters through well known switching mechanisms or multicoupling which will provide energization thereof either individually or in concert. Proper assembly and tuning as deemed necessary to produce optimum impedance and radiation patternsfor any given *location and operation produce exceptional results with minimum interference, even though the discage antenna array inphysically disposed in a limited space.

.Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It'is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A discage antenna array adapted to broadcast electromagnetic energy over a broad range of frequencies comprising in combination a first coaxial transmission line having outer and inner conductors, a disc antenna disposed at one end of said transmission line and electrically connected to the outer conductor thereof, a very high'frequency antenna mounted 'onsaid disc antenna for electromagnetic isolation therebetween and electrically coupled to the inner conductor of said first coaxial transmission line, an apertured bazooka stub transformer spacially disp'osedfrom but in contiguous relationship with said disc antenna surrounding said first coaxial transmission line'nar the other extremity thereof, a fat cage antenna symmetrically surrounding and spatially disposed from said first coaxial transmission line interconnecting the aforesaid bazooka stub transformer and conductive ring, support surface means, mounting means connected to the other end said first coaxial transmission line for securing same to saidr'support surface means, a second coaxial transmission line having outer and inner conductors, said outer being coupled to said bazooka stub transformer at an aperture therein, said inner conductor extending through said aperture and connected to the outer conductor of the aforesaid first coaxial transmission line, and conductive means attached to'said conductive ring and said fat cage antenna for feeding electromagnetic energy thereto.

2. A broadband discage antenna system comprising in combination a coaxial transmission mast having outer and inner conductors, a support surface, means for securing the outer conductor of said coaxial transmission mast to said support surface, a disc antenna mounted on and electrically coupled to the end of the outer conductor of said coaxial transmission mast opposite said support surface, a one-quarter wave stub transformer spatially disposed from but in close proximity with said disc antenna and surrounding said coaxial transmission mast, a conductive ring concentrically surrounding but insulated from said coaxial transmission mast adjacent the aforementioned support surface and securing means, a substantially diamond shaped cage antenna electrically interconnecting said transformer and said conductive ring, a very high frequency antenna mounted on but electromagnetically isolated from said disc antenna electrically coupled to the inner conductor of said coaxial transmission mast at the end thereof opposite said support surface, and means for feeding energy to each of the afore- References Cited in the file of this patent UNITED STATES PATENTS 2,102,410 Flyer Dec. 14, 1937 2,158,875 Leeds May 16, 1939 2,267,889 Aubert Dec. 30, 1941 2,393,218 Caraway Ian. 15, 1946 2,756,420 Kolar et a1. July 24, 1956 FOREIGN PATENTS 935,558 Germany Nov. 24, 1955 OTHER REFERENCES Kraus: Antennas, McGraw-Hill Book Co., Inc., 1950, pp. 420-421.

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