US2557941A

US2557941A - Directive antenna

Info

Publication number: US2557941A
Application number: US603688A
Authority: US
Inventors: Anthony M Casabona
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC; Federal Telephone and Radio Corp
Priority date: 1945-07-07
Filing date: 1945-07-07
Publication date: 1951-06-26
Anticipated expiration: 1968-06-26

Description

June 26, 1951 A. M. CASABONA 2,557,941

E DIRECTIVE ANTENNA Filed July 7, 1945 v s Sheets-Sheet 1 ATYURNEY June 26, 1951 CASABQNA 2,557,941

DIRECTIVE ANTENNA Filed July 7, 1945 s She eis-Sheet 2 ATTORNEY June 26, 1951 CASABONA 2,557,941

DIRECTIVE ANTENNA Filed July 7, 1945 's Shets-Sheet s IN VEN TOR. 45 ANTHONY M. C/isflam/A NY m ATTORNEY Patented June 26, 1951 DIRECTIVE ANTENNA Anthony M. Casabona, New York, N. Y., assignor to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware Application July 7, 1945, Serial No. 603,688

4 Claims.

This invention relates to composite antennas and more particularly to directive antenna systems of a type dependent upon the resultant field radiation produced by directly energized antenna arrays in combination with parasitically energized antenna array or reflectors.

' In certain cases a sharply directive pattern of relatively small azimuth angle is desired having relatively high front-to-back ratio. If the parasitic members of the array constituting the reflectors are tuned to maximum reflection, the propagated signal is radiated in a desired direction having a horizontal and vertical directivity. In such a system the power output requirements of the transmitter are low and at the same time interaction between the directive antennas and other nearby antennas is eliminated. However, in order to insure maximum efficiency in such a system the antenna array must be constructed so as to eliminate any possibility of detuning due to changes in electrical characteristics. A rigid form of construction thus prevents undesirable variation in characteristics except those encountered when the array is subjected to accumulations of ice or snow on the radiating members. An antenna array utilizing a reflector varies in radiation resistance according to the spacing between the fed radiator and reflector. This property is useful in matching the array to feeder lines. The dimensions of the array can be established from known formulas one of which I include to compute the dimensions of a dipole array operative over a required frequency band (having a desired horizontal radiation pattern), and which will produce zero signal 40 from the azimuth angle at which maximum signal is obtained.

Having designed an antenna of the type above mentioned, its pattern may still be subject to some change due to various causes such as the weather conditions above mentioned. In order to maintain constant such a pattern, it is necessary to provide those features in the structure which will tend to minimize or prevent changes in the pattern arising from the physical conditions mentioned, or other causes.

It is an object of my invention to provide an antenna array having a high front-to-back ratio with the major lobe sensed in such a manner as to produce and maintain a horizontal pattern of zero signal a small number of degrees from the azimuth angle at which maximum signal is obtained.

It is a further object of my invention to provide an antenna array incorporating certain improvements in construction so as toprovide a rigid assembly which will prevent and eliminate variations of electrical characteristics due to changes in dimensions, variations in separation of constituting members of the array, or fragile design.

It is still a further object of my invention to provide an antenna array electrically designed and assembled so as to render negligible the losses in radiation power due to the accumulation of ice or snow on the exposed portions of the array which form the radiating surfaces.

It is an additional object of my invention to provide an antenna array electrically designed and assembled so as to reduce the detuning efi'ect of any accumulation of ice or snow on the radiating members of the antenna or on the junction points of the radiating members with their respective supporting systems.

Still another object of my invention is to provide an antenna assembly so designed as to possess a lumped capacity of relatively high value at the fed ends of each dipole thereby allowing matching stubs and shorting bars to be of compact size, contributing to the small size necessary for the enclosing shield around the ends of each dipole, the matching stubs, and shorting bars.

According to a feature of my invention, I provide an antenna consisting of four dipole antennas two of which are fed and are spaced substantially electrical degrees,

apart in the vertical plane while the alternate dipoles are utilized as reflectors, being spaced apart in a vertical plane an equivalent number of degrees and also being spaced behind the fed membersv or main radiators a predetermined amount, and tuned in such a manner as to ive a high front-to-back ratio. The vertical spacing of 180 electrical degrees provides for minimum radiation above and below the array, and, as may be concluded, the combination of horizontal and vertical directivity allows for maximum directive radiation usinga minimum of power.

The antenna units are supported at their innermost ends by two shield boxes, and are electrically insulated from these shield boxes by insulating bushings or suitable low loss material. The dipoles being center fed allows for a form of construction in which the inner end of about two inches of each antenna rod is enclosed in a shield box. This portion of each rod thereforedoes not radiate but contributes to the establishment of a large lumped capacity between the two antenna 'shield box.

As an illustrative instance, according to a feature of my invention, the desired radiation pattern for a specific application was secured by utilizing known formulas and the general equation determining the horizontal pattern of a dipole of any length 2L:

sine (l sine ][sine +sine 0?] COS 0 where L is one-half of the total length of the dipole. Using this equation it is possible to compute the size of a dipole which will produce zero signal 40 degrees from the azimuth angle at which maximum signal is obtained. The total length 2L of the dipole is found to be 440 degrees. By reducing the spacing between the fed radiator and reflectors from approximately -9() electrical degrees to 35 electrical degrees a point will be reached at which the maximum front-toback ratio is obtained, while the reflector stubs are tuned to assist in obtaining'this front-toback ratio. The fed-radiator stubs are tuned to match the line impedance.

In this manner a directive, sharp pattern was secured as the signal increased from zero to maximum in 40 degrees azimuth angle.

Abetter understanding of my invention and the objects and features thereof may be had by referring to the accompanying drawings, in which:

Fig. 1 is a front view in partial section;

Fig. 2 is a side view in partial section;

Fig. 3 is a top plan view of the uppermost shield box A with the cover removed; and

Fig. 4 is a bottom plan view of the lower'box B with the cover removed.

Turning first to Fig. 1 there is shown generally the central portion of the directive antenna array in which directly fed dipole antenna elements I, 2 and 3, 4 are shown mounted in shield boxes 5, 5 which are made of conductive material.

Likewise, parasitically fed dipole antenna ele-- ments 1, 8 and 9, it are spaced approximately 35 behind the directly fed dipoles in the same shield boxes 5, 6, as shown in Fig. 2. Each antenna element is supported in and insulated from the shield box by insulated bushings ll secured to shield box by screws l2. As may be seen from the view of shield box 5, the inter-- mediate ends of the antenna elements such as I and 2 are brought closely together to effect a high degree of capacitive coupling. Terminals f 3 are placed on the endof each element to effect electrical connection to a transmission line l4, preferably of shielded dual beaded line, as well as being the junction points of short tuning stubs l5 adjustably tuned by means of shorting bars IS. The transmission line 14 electrically interconnects antenna elements I, 2 only, thereby enabling them to be energized to act as radiators. Similar connections exist inside shield box 6, with antenna elements 3, 4 being energized through transmission line (4. Midway the length of transmission line 24 there are feed line terminals ll for connection to feed line l8 which extends vertically downward iromjunction box 19 directly through the center of shield box 6, terminating in a screw-capped coupling unit 26 for connection to a line of any length. Shield boxes 5 and 6 are arranged vertically one above the other, and spaced apart in such a manner that the spacing between the contained dipoles shall be substantially a half-wavelength at the operating frequency. Enclosing beaded line H are two sections of tubing 2i and 22 joined together by junction box l9, with their flanged ends 23 fastened to shield boxes 5 and 6 by screws 24. A length of tubing 25 encloses feed line 18 between junction box [9 and lower shield box 6. These tubular sections add strength and rigidity to the array, as well as ensuring weatherproof electrical connections. To enable electrical connections to be made, shield boxes 5 and 6 are provided with covers 26, 27 and sealing

gaskets

28, 29, the covers being held in place by screws 30. The antenna elements I, 2, 3, 4 and i, 8, 9, It, are of equal length, each being approximately 220 in length. When mounted, the distance between their ends is approximately 440, this length being determined by formula to produce a desired pattern.

Mounted 90 from the ends of the antenna elements and rigidly spacing the parasitic element from the fed element are low loss dielectric spacers 3|, as shown in Figs. 3 and 4. The spacers consist of two

rectangular portions

32 and 33 held tightly clamped to the antenna element by means such as bolts 34, lock washers 35, and hex nuts 36. In this manner a spacing approximating 35 between adjacent elements is maintained.

As may be seen best in Fig. 2, 'the tuning stubs and shorting bars for the parasitic antennas 'l, 8 and 9, it] are contained within

tubular sections

31 and 38, mounted on shield boxes 5, 6 at their flanged ends 39 and 40 by screws M. In order to further strengthen the array, supporting struts 42 are fastened to the back of shield boxes 5, 6 by means such as screws 43 and lock washers 44. Adjustable clamps 45 are fastened to these supporting struts by bolts 46 and clamping plates 41, for mounting the entire array on a pole or mast.

As will be seen, the proximity of the intermediate ends of the antenna elements within the shield boxes serves to increase capacitive couang; In addition, the enclosed portions of each element lies adjacent to a portion of the shield box, thereby affording more capacitive coupling, resulting in a high degree of lumped capacity at this point. This enablesrelatively short tuning stubs to be used, affording compact design.

As is well known in the art, the best receiving antenna is a well-designed efiicient transmitting antenna. While I have described my invention primarily as a transmitting array, it is clear that the same may be used as a receiving array of maximum efficiency at the operating frequency.

While I have disclosed as a particular embodiment of this invention a possible structural example, many variations in the detail and assembly thereof may be had without departing from my invention. It should be understood that this specific example is made merely by way of example,'and is not intended as a limitation on my invention as set'forth in the objects thereof and the attached claims.

I claim:

l.-A directiveantenna system comprising a pair of component antennas spaced thirty-five electrical degrees with respect to the operating frequency in the horizontal plane, one of said antennas forming a dipole energized to act as a primary radiator, transmission line means for energizing said dipole, the other antenna acting as a parasitic dipole or reflector, conductive shielding and supporting means enclosing the central portions of each dipole, insulatedly supporting and aligning said dipole antennas, and effecting substantial capacitive coupling between said central portions and said shielding means adjustable tuning means for said dipole antennas within said shielding means for tuning the energized dipole to present a matched impedance to the line, corresponding tuning means connected between the adjacent ends of the parasitic dipole to secure a maximum front-to-back ratio of reflection, said shielding means effectively preventing radiation from and increasing lumped capacity between the central portions of said pair of dipole antennas, the lumped capacity at this point offsetting the detuning elTect of any small additional amount of capacity that may occur external to said shielding means.

2. A directive antenna system comprising four dipole antennas arranged in pairs, conductive shielding means for the central portion of each pair of said dipoles, said dipoles being insulatedly supported and'shielded over a predetermined length of said central portion by said conductive shielding means whereby substantial capacitive coupling is efiected between said central portion and said shielding means, said antennas being spaced to effectively produce a rectangular array, transmission means electrically interconnecting two of said dipoles lying in the same vertical plane for applying energy to said dipoles for radiation, a feed line coupled to said transmission means, tuning means to tune said dipoles to present a matched impedance to said feed line, and other tuning means for tuning the remaining two dipoles to effectively secure maximum front to back radiation ratio.

3. A directive antenna system adapted for operation at a given wavelength comprising four dipole antennas arranged in pairs, conductive shielding means for the central portion of each pair of said dipoles, said dipoles being insulatedly supported and shielded over a predetermined length of said central portion by said conductive shielding means, units of said conductive shielding means being spaced one hundred and eighty electrical degrees at said operating frequency apart in the vertical plane, the dipoles of each pair being spaced substantially thirty-five electrical degrees at said operating frequency apart in the horizontal plane thereby effectively producing an array of rectangular shape, transmission means electrically interconnecting two of said dipoles lying in the same vertical plane for applying energy to said dipoles for radiation, a feed line coupled to said transmission means, tuning means to tune said dipoles to present a matched impedance to said feed line, and other tuning means for tuning the remaining two dipoles to effectively secure maximum front-to-back radiation ratio.

4. A directive antenna system comprising a plurality of dipole antennas substantially arranged to define a rectangular solid being spaced in the vertical plane and in the horizontal plane, said dipole antennas forming an array having two dipoles energized to act as radiators, transmission line means for energizing said dipoles, said array having two dipoles acting as parasitic elements or reflectors, conductive shielding and supporting means enclosing the central portions of each pair of horizontally spaced dipoles insulatedly supporting and aligning said dipole antennas and effecting substantial capacitive coupling between said dipole antennas and said shielding means, adjustable tuning means for said pair of said dipole antennas within said shielding means for tuning the energized dipoles to present a matched impedance to the line, corresponding tuning means for tuning the parasitic dipoles to secure a maximum front-to-back ratio of reflection, said shielding means effectively preventing radiation from and increasing lumped capacity between the central portions of said pair of dipole antennas, the lumped capacity at this point offsetting the detuning effect of any small additional amount of capacity that may occur external to said shielding means.

ANTHONY M. CASABONA.

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

UNITED STATES PATENTS Number Name Date 2,166,100 Sullinger July 11, 1939 2,177,416 Alford Oct. 24, 1939 2,183,784 Carter Dec. 19, 1939 2,238,245 Brown Apr. 15, 1941 2,240,298 Heindel et al. Apr. 29, 1941 2,251,997 Goldmann Aug. 12, 1941 2,255,520 Schuster Sept. 9, 1941 2,268,640 Brown Jan. 6, 1942 2,272,608 Hoffman Feb. 10, 1942 2,350,916 Morrison June 6, 1944 2,380,519 Green July 31, 1945 2,419,552 I-Iimmel et al Apr. 29, 194'? 2,436,843 Watts et al. Mar. 2, 1947