US 3761934 A
A two-element antenna having front and rear antenna elements arranged in parallel relationship. Perpendicular elements on the ends of the front and rear elements with the rear ends of the perpendicular elements of the front antenna element being spaced from one to five percent of the wave-length of the received frequency from the front ends of the perpendicular elements on the rear antenna element.
Description (OCR text may contain errors)
United States Patent [191 Terakawa 1 TWO-ELEMENT RECEIVING ANTENNA WITH CRITICALLY SPACED END SECTIONS  Inventor: Koichi Terakawa, Tarumi-ku, Kobe,
Japan  Assignee: DX Antenna Company, Limited,
Kobe, Japan  Filed: May 8, 1972 211 Appl. No.: 251,360
 US. Cl. 343/752, 343/818  Int. Cl. HOlq 9/00  Field of Search 343/752, 792.5, 802,
[ 56] References Cited UNITED STATES PATENTS 2,563,243 8/1951 Hills 343/818 [4 1 Sept. 25, 1973 3,389,396 6/1968 Minerva et a1 343/792.5 3,543,277 11/1970 Pullara 1 343/802 2,558,145 6/1951 Mock 343/802 Primary ExaminerEli Lieberman At!0rneyEugene E. Geoffrey, Jr.
 ABSTRACT A two-element antenna having front and rear antenna elements arranged in parallel relationship. Perpendicular elements on the ends of the front and rear elements with the rear ends of the perpendicular elements of the front antenna element being spaced from one to five percent of the wave-length of the received frequency from the front ends of the perpendicular elements on the rear antenna element.
2 Claims, 3 Drawing Figures TWO-ELEMENT RECEIVING ANTENNA WITH CRITICALLY SPACED END SECTIONS This invention relates to a two-element receiving antenna and more specifically to an antenna structure comprising a folded dipole type half-wave doublet antenna and a single parasitic reflector of the same type, each having a pair of ring-like members at both ends.
As described in the article by G. H. Brown entitled Directional Antenna", I.R.E., January 1937, the power gain of a two-element antenna having a single parasitic element whether used as a reflector or a director, cannot be maximum when the distance between the both elements is equal to a quarter wave-length and increases with further reduction of the distance. For example, a large gain is obtained at this distance within a range of 12 to percent of the wave-length. On the contrary, however, the input impedance is lowered and the frequency band characteristic becomes narrow at such a short distance between the elements. Therefore, though it may be allowable when only a specific frequency is concerned as in the case of transmitting antenna, it is absolutely necessary to insure the gainfrequency characteristic and gain-impedance characteristic by expanding the distance between the elements even at the sacrifice of gain when a wide coverage is required as in the case of a TV receiving antenna. Therefore, it becomes essentially desirable to improve the power gain or a receiving antenna without reducing the distance between both elements.
Accordingly, one object of this invention resides in the provision of a two-element receiving antenna structure having improved power gain.
It has been known that the space occupied by a twoelement doublet antenna can be reduced remarkably by adopting a folded type and attaching a pair of lateral ring-like members to both ends. It has been found experimentally with this invention that the power gain of such an antenna is remarkably improved when the distance between the adjoining ring-like members respectively attached to the main antenna element and the parasitic reflector element is within a specific range relating to the wave-length concerned. According to this invention, this distance is selected as small as the order of one to five percent of the wave-length.
These and other features of this invention will be described in detail hereinunder with refernce to the accompanying drawings.
In the drawings:
FIG. 1 is a perspective view representing an example ofa two-element receiving antenna in which the principle of this invention is embodied;
FIG. 2 is a schematic plan view of the antenna of FIG. 1 representing a relative disposition of the structural components; and
FIG. 3 is a gain-frequency characteristic diagram of the antenna of FIG. 1 presented for an aid of explaining an effect of this invention.
Referring to FIG. 1, a horizontal connecting rod 3 is fixed to an antenna pole 1 through a fixture 2 and a main radiator element and a parasitic reflector element are fixed respectively to both ends of the connecting rod 3 through fixtures 4 and 6. The radiator element is composed of a pair of horizontal rods 5 arranged in parallel in a vertical plane which is perpendicular to the connecting rod 3 and a pair of elongated ring-like members 9 are fixed to both free ends of the horizontal rods 5 through fixtures 8 so as to lie in two vertical planes which are perpendicular to the vertical rods 5. The parasitic reflector element is composed of a pair of horizontal rods 7 and a pair of elongated ring-like members 11 which are arranged in the same manner as in the case of the radiator element through fixtures 10.
A typical example of the geometries of the antenna structure is as follows, with reference to FIG. 2.
Distance between both elements (D): 680 millimeters Span of radiator element (S1): 834 millimeters Span of reflector element (S2): 994 millimeters Length of ring-like members 9 and 11: 520 millimeters Width of ring-like members 9 and 11: 100 millimeters Distance between horizontal rods: 50 millimeters Within a frequency range of 76 to megaherz, the above geometries of the antenna structure give a uniform impedance characteristic and insure a sufficient receiving frequency band width.
From the above basic geometries, the spans S1 and S2 of both elements and the length of the ring-like element were successively changed to vary the distance between the rear end of the ring-like member 9 of the radiator and the front end of the ring-like member 11 of the reflector, which is indicated by d in FIG. 2. At the seme time, the power gain was plotted with respect to the receiving frequency and the gain-frequency characteristic diagram of FIG. 3 was thus obtained. In the diagram, curves A, B, C and D correspond respectively to four variations of the distance d, which are 1.12, 2.24, 3.36 and 4.62 percent of the wave-length corresponding to the center frequency 83 Mhz. The dotted curve E corresponds to a regular equi-interval folded two-element antenna combined with an extension coil so as to give the same aperature area and was presented for the purpose of comparison.
The most preferable characteristic in FIG. 3 is that shown by curve C. Since the power gain of a regular equiinterval antenna having the same aperture area is about one decibel throughout the frequency range, the antenna structure corresponding to curve C gives a power gain as high as about 3.5 times at the lowest frequency and 2.5 times at the highest frequency of the receiving frequency range. The curves A, B and D also represent improved gain-frequency characteristics though they are somewhat inferior to curve C. Therefore, it can be said that an improved gain-frequency characteristic is obtainable when the distance d is selected within a range of about one to five percent of the wave-length corresponding to the center frequency. When the distance d is selected greater than five percent of the wave-length, the gain drops abruptly at high frequencies as shown by curve D. On the contrary, when the distance d is selected to be less than one percent of the wave-length, the gain drops down in the low frequencies as shown by curve A. When the rear end portion of the ring-like member 9 of the radiator and the front end portion of the ring-like member 11 of the reflector come in superposition in the direction of the receiving wave, the gain characteristic is disturbed to form unstable peaks and the antenna structure becomes unusable.
In the case of horizontal reception by a regular antenna, the span of the antenna should be about two meters in order to cover the above mentioned frequency range, and a large space for installation is required. According to this invention, however, the span is substantially halved and the required space for installation is substantially reduced. Moreover, the antenna of this invention has such a superior feature that a high gain is maintained notwithstanding the fact that the aperture area is almost halved.
In the above embodiment, the ring-like members 9 are fixed symmetrically to the horizontal rods 5. However, this is based upon a consideration for conserving the original eight-type directional characteristic of the main antenna as a half-wave dipole antenna, and the ring-like members 11 of the reflector need not be symmetrical. Further, the reason why the main radiator element is provided in a folded dipole type is to make its impedance 300 ohms. Therefore, the reflector element need not be of such a folded type and may be rodshaped. In this case, the same operational effect can be expected even if the member 1 l is rod-shaped. Morever, though the above description is made in conjunction with the case wherein the parasitic element is used as a reflector, this invention is also applicable to the case wherein it is used as a waveguide element.
What is claimed is:
l. A two-element receiving antenna comprising front and rear antenna elements arranged in parallel with each other on a connecting rod, and two pairs of elongated ring-like members respectively attached to the ends of said antenna elements and arranged laterally to said elements, the distance between the rear end of said ring-like member of the front antenna element and the front end of the rear antenna element being selected within a range of one to five percent of the wave-length corresponding to the receiving frequency.
2. A two-element receiving antenna comprising front and rear antenna elements arranged in spaced parallel relationship, a connecting rod supporting said elements, and elongated members attached to the ends of said elements and disposed transversely thereof, the distance between the front end of each rear antenna member and the rear end of each adjoining front antenna member being selected within a range of one to five percent of the wave-length corresponding to the receiving frequency.