US 2774967 A
Description (OCR text may contain errors)
Dec. 18, 1 956 F. J. LUNDBURG BALANCED DOUBLET ANTENNA OF SMALL DIMENSION Filed Nov. 19
INVENTOR FRANK d. LUNDBURF! ATTORNEY United State atent BALANCED DOUBLET ANTENNA OF SMALL DIMENSION Frank J. Lundburg, East Orange, N. J., assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application November 19, 1949, Serial No. 128,332
Claims. (Cl. 343-818) This invention relates to radio antennas and more particularly to antennas made of small dimensions.
For convenience of construction and installation it is often desirable to have antennas made of small dimensions. This is particularly desirable when an antenna of directive characteristics is wanted, as the small construction makes physical rotation at relatively high speed practical. A difficulty arises however in the use of antennas having a length short with respect to a wave length. Such antennas have a generally low radiation resistance and so are not matched with the transmission line, thus resulting in inefliciency of operation.
It is an object of my invention to provide a relatively small easily rotatable antenna, and to use therewith a device for rendering the antenna eificient despite its small dimensions.
According to a feature of my invention I provide an antenna of relatively small dimensions, for example, a dipole in the order of from one to three-tenths overall wave-lengths, and supply about the antenna a loading resonator effectively open about one planar dimension of the antenna to provide a substantial impedance match between the antenna and the transmission line. The resonator may comprise an open wire cage made of rods perpendicular to the plane of polarization of the antenna covered at the top and bottom with plane conductive sheets. The antenna may be rotated within the cage resonator construction.
While I have set forth above the objects and features of my invention the operation thereof may be best understood from the description of a particular embodiment thereof made with reference to the accompanying drawing, the single figure of which shows an antenna incorporating features of my invention.
In this figure is shown a dipole antenna 1 supplied with energy over a coupler 2, connected to a feed line 3. Conductive plates 4 and 5 are spaced below and above dipole antenna 1, and these plates are interconnected by the rods 6, fastened to plates 4 and 5 to provide mechanical separation and electrical connection thereto. A rotary mounting may be provided as shown at 7 so that the antenna may be rotated independently of the resonator. The length of the dipole antenna may be of any desired length preferably between one twentieth and three tenths wave lengths. The plates and connecting wires form a cavity resonator which serves to raise the impedance of the antenna assembly to produce an elfective match between the radiating structure and the ether. The tie rods are closely enough spaced to form effectively a closed resonator and a polarizing grating to filter the vertically polarized components. Horizontally polarized energy, however, readily passes out around the periphery. While the assembly is completely matched at only one frequency, it is efiective over a relatively wide band with permissible mismatch.
2,774,967 Patented Dec. 18, 1956 In an actual example of a dipole radiator of substantially 30 electrical length at 800 megacycles was provided. This dipole had a. radiation resistance of three to four. ohms by itself giving very low efliciency radiation. A resonator cage was provided symmetrically about the dipole, the spacing between the plates being substantially a half wave length at the operating frequency and the diameter of the circle being likewise of the same dimensions. Twenty rods spaced uniformly around the periphery were used. With this arrangement a radiation resistance of approximately 44 ohms was achieved. This antenna was operated successfully over a wave band of approximately 60 megacycles with a mismatch of approximately 2:1.
While the specifiic example described covers a structure which was found very good it should be understood that the particular dimensions are not controlling.
It is clear that the principles of the invention may be achieved by other structures. The dimensions of the resonator may vary widely, it being borne in mind that the essential feature is to provide a loading resonator for the short dipole to elfect a desired impedance transformation. Also while any particular structure will have an optimum effect at the center frequency it is to be understood that the efiective tolerence of mismatch will permit operation over a relatively wide frequency band with reasonable efliciency. Although the particular example given is in the range of 800 megacycles it is clear that the invention may apply to lower frequencies as well, where the normal dimensions are greater so that the reduction in dimensions is of greater importance from a standpoint of ready rotatability.
1. A radio antenna assembly for radiating a plane polarized wave, comprising a radiating dipole antenna of small length relative to half a wave-length at the operating frequency, and a resonator including conductive vertical supports physically enclosing said antenna but open to radiation in said plane of polarization.
2. A radio antenna according to claim 1, wherein said dipole is between one twentieth and three tenths wave length long at the operating frequency.
3. A radio antenna assembly comprising a dipole radiator having an overall length short with respect to a quarter wave length at the operating frequency, a pair of conductive plates spaced apart on opposite sides of and substantially concentric with a perpendicular axis of said dipole, and a plurality of spaced rods interconnecting said plates and arranged in a circular pattern, and regularly spaced from one another at substantially a tenth wave length, said plates and rods forming a resonator cage substantially matching the impedance of said antenna to the radiation space at said operating frequency.
4. A radio antenna assembly comprising a dipole radiator having an overall length between one twentieth and three tenths wave length at the operating frequency, a pair of conductive plates spaced apart a half wave length at the operating frequency on opposite sides of and substantially concentric with a perpendicular axis of said dipole, and a plurality of spaced rods interconnecting said plates and arranged in a circular pattern of substantially one half a wave length diameter at the operating frequency, and spaced from one another substantially a tenth wave length.
5. A radio antenna assembly comprising a radiating antenna of small length relative to half a wave length at the operating frequency and capable of producing directive, substantially plane polarized radiations, a resonator comprising a pair of plates having conductive sur- 3 t faces spaced on opposite sides of said antenna, and a plurality of conductive rods perpendicular to the plane of polarization of said dipole, spaced around the antenna and connected to said plates.
References Cited in the file of this patent UNITED STATES PATENTS 4 Katzin Apr. 9, 1946 Hansen Feb. 4, 1947 Montgomery Mar. 25, 1947 Aram Mar. 29, 1949 Johnson Dec. 5, 1950 Wehner Jan. 30, 1951 Litchford et a1 Oct. 23, 1951 FOREIGN PATENTS Australia Dec. 9, 1941