US2485138A

US2485138A - High-gain antenna system

Info

Publication number: US2485138A
Application number: US701011A
Authority: US
Inventors: Philip S Carter
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1946-10-03
Filing date: 1946-10-03
Publication date: 1949-10-18
Anticipated expiration: 1966-10-18

Description

Oct. 18, 1949. P. s. CARTER HIGH-GAIN ANTENNA SYSTEM Filed Oct. 3, 1946 I INVEINTOR Grier 7%. W

ATTORNEY Patented Oct. 18, 1949 .Philip 8568M,

Delaware Port Jefferson, 1N. Ernest ne: to Radio Corporation-'01 America,

a. corporation of Application October 3, 19%, WIND. 1!;01'1 2 Claims. (Cl. 6250-3365) The present invention relates to antennas and more particularly to simple, readily adjusted, directive antenna systems.

An object of the present invention-is to provide a simple directive antenna having high gain and negligibly small back radiation.

Another object of the present invention is the provision of an antenna. 'as aforesaid which .re- .quires a'minimum of adjustments.

Still another object of the present invention is the provision of a directional antenna which is ruggedly constructed.

The foregoing objects and others which :may appear from the following detailed description are attained by providing an antenna system including a metallic screen with an energized dipole radiator a short distance in front of the screen and a parasitic dipole parallel to the energized dipole and located a half wave in front of the screen. Such an antenna arrangement is very simply adjusted for optimum operating characteristics and the measured gain is higher than that of a number of antennas of the Yagi type which were compared therewith. The Yagi type of antenna has an appreciable back radiation and usually contains 5 or 6 or more radiating elements, all of these elements being critical in adjustment. The antenna of the present invention contains only two adjustable antennas, one directly fed and one parasltically excited.

The present invention will be more fully understood by reference to the following detailed description in which:

Figure 1 illustrates in perspective view an embodiment of the present invention, while Figure 2 is a radiation pattern in the electric plane of the antenna of Figure 1 compared with the radiation in the electric plane from a simple reflecting plate and dipole arrangement, and

Figure 3 is a radiation pattern similar to Figure 2, except that it is taken in the magnetic plane.

Referring now to Figure 1 there is shown a reflecting plate P which may be constructed of a wire mesh. For best results the mesh should not be coarser than about 6 wavelength spacing between the wires. An antenna, which was actually constructed, and tested, used a reflecting plate having dimensions of the order of 1 /2 wavelength square. sions are of the order of one wavelength long by a half wavelength high. Arranged on a metallic supportin rod S and spaced in front of reflecting plate P, a distance approximateiy equal to wavelength, is a folded dipole radiator l0 hav- The minimum practical dimendue mitweasily extending arms H and it. The rspacmg of the ranergized unit m mm screen LP is not critical. Two itenths or m wavelength as shown in Figure 1 is a good practical compromice. Gloser spacings result in decreased iradiaitiufl resistance and lowered emciency more than counterbalmctng the somewhat higher theoreticaigain resulting theretrom. Fiihe antenna is sted tram transmission :line 11b. The transmission line is shown hem as lining a two-wire rom transmiaion tine, thus directly :giving a abalanoedieed tothe folded dipole I8. ld'lm'thermore wire tranniission il'me may i]!!! so amnstructed as to iiirwtlw match #the high input impedance the folded dipole. However, if 'desired, a straight dipole and .a coaxial teed time may be used. Also arranged on rod S and in front of dipole radiator l0 and parallel thereto at a distance from the screen equal to nearly a. half wavelength is a parasitically energized radiator I4. The radiator I4 is cut somewhat shorter than a half wavelength long. Preferably it is supplied at each end with adjustable sleeves 24 whereby it may be tuned to the optimum operating condition.

Now, at first consideration, it may not be apparent why the additon of a parasitically energized radiator, such as radiator l4, or an antenna. fed in any phase relationship whatever with respect to the main radiator and at a spacing from the screen of wavelength, would give any appreciable gain. A dipole spaced /2 wavelength from the screen gives zero radiation in the direction perpendicular to the screen. The high gain actually resultin from the present arrangement may be explained by the fact that the field from the parasitical radiator I4 is approximately in phase opposition to the field from the energized radiator ID, thus greatly reducing the overall radiation in directions off to the sides from the direction normal to the plane of reflector P. The parasitic radiator I4 is adjusted to be a little on the short side of resonance in order to obtain a current in the radiator approximately in phase opposition to the current in the energized unit IB. In an embodiment actually tested maximum results were obtained when the length of the parasitic radiator was approximately 0.45 wavelength while the theoretical length for resonance would be 0.48 wavelength.

In Figure 2 I have shown the measured radiation pattern in the electric plane obtained by using the present invention. This is illustrated in curve 20. The measured radiation obtained from a simple plate and dipole radiator is shown by curve 2|. It will be noted that nearly twice as much radiation is obtained in the direction normal to the plane of the reflector plate with the present antenna as is obtained with the previously known plate and dipole combination.

Similarly, Figure 3 shows in curve 30 the measured radiation in the magnetic plane obtained by utilizing the present invention while curve 3| shows the measured radiation pattern of the simple plate and dipole arrangement. Here again it will be noted that approximately a 2: power gain over the simple plate and dipole arrangement is obtained by utilizing the present invention. The power gain is nearly 8:1 over a dipole in free space.

While I have illustrated a particular embodiment of the present invention, it should be clearly understood that it is not limited thereto since many modifications may be made in the several elements employed and in their arrangement and it is therefore contemplated by the appended claims to cover any such modifications as fall within the spirit and scope of the invention.

What is claimed is:

1. In an antenna system, a conductive screen, a first radiator member in front of said screen a distance of substantially .2 wavelength and a second radiator member parallel to said first radiator and at a distance from said screen of substantially a half wavelength, said first radiator being a folded dipole, and transmission line means coupling said first radiator to a source of high frequency energy, and a straight metallic supporting member extending normally from said screen and attached to the center of said first radiator member for support thereof.

2. In an antenna system, a conductive screen, a first radiator member in front of said screen a distance of substantially .2 wavelength and a second radiator member parallel to said first radiator and at a distance from said screen of substantially a half wavelength and transmission line means coupling said first radiator to high frequency energy transducer means, said second radiator being parasitically excited and having a length slightly less than a half wavelength and at which the current therein is approximately in phase opposition to that in said first radiator and a metallic supporting rod extending normally from said screen and attached to the center of said first radiator member and the center of said second radiator member for the support of said radiators members.

PHILIP S. CARTER.

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

UNITED STATES PATENTS Number Name Date 2,163,770 Von Radinger June 27, 1939 2,204,175 Carter June 11, 1940 2,370,053 Lindenblad Feb. 20, 1945 2,407,057 Carter Sept. 3, 1946 OTHER REFERENCES Radio News (Engineering edition), April 1946, page 20.