US 3096520 A
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July 2, 1963 w. EHRENSPECK 3,096,520
ENDFIRE ARRAY Filed March 6, 1958 v 2 Sheets-Sheet 1 HERMANN WE|W80K WW M MM/VAV ATTORNEYS y 1963 H. w. EHRENSPECK 3,096,520
ENDFIRE ARRAY .Filed March 6, 1958 2 Sheets-Sheet 2 o o o o o 0 2O 0 o o o o o o o o 0 \2"-0 O O o o o o 0 o icyo o b o o o o o o o o o o o o w 3 o o o o o o o QZB o o o o o o o o o 0 2 0 o o o 0 INVENTOR. HERMANN W.EHRENSPECK ML...- q
AT ORNEYS United States Patent 3,096,520 ENDFIRE ARRAY Hermann W. Ehrenspeck, 94 Farnham St., Belmont 78, Mass. Filed Mar. 6, 1958, Ser. No. 719,698 2 Claims. (Cl. 343-834) (Granted under Title 35, US. Code (1952), sec. 266) t The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without payment to me of any royalty thereon.
This invention relates generally to antennas and more particularly to a method and means for controlling the amplitude and phase across a virtual aperture.
Endfire arrays, such as Yagi antennas, may be analyzed in terms of the amplitude and phase distribution in a virtual aperture plane transverse to the array axis and located at the end of the array. Arrays of this type usually have high side lobes like horns which, according to my invention, may be reduced by afiecting the amplitude and phase distribution in the virtual aperture of the endfire array.
According to the teachings of my invention, both amplitude and phase distribution may be aifected by placing one or more parasitic side rows on both sides of the center array, thus transforming the array into a two-dimensional array.
The utilization of the parasitic arrays of my invention provide a reduction in side lobes, increased gain, and increased bandwidth with respect to pattern.
It is, therefore, an object of my invention to produce a novel method and means for reducing side lobes of an antenna pattern.
It is another object of my invention to produce a novel endfire array having good side lobe reduction and increased gain.
It is still another object of my invention to produce a novel method and means for increasing antenna bandwidth with respect to pattern.
It is a further object of my invention to provide a novel method and means for producing side lobe reduction which may be applied to existing endfire arrays.
It is a still further object of my invention to produce \a novel means for side lobe suppression not requiring additional feed systems.
Another object of my invention involves the utilization of parasitic side rows to a center array in the vertical as well as horizontal direction to improve pattern and gain performance.
Still another object of my invention involves the utilization of \a novel means for side lobe reduction applicable to both high and low frequency antennas.
A further object of my invention involves the production of an antenna suitable for use for scatter propagation.
These and other advantages, features and objects of the invention will become more apparent from the following description taken in connection with the illustrative embodiments in the accompanying drawings, where- FIGURE 1 is a representation of an antenna array with two parasitic side rows;
FIGURE 2 is a plan view of a two-dimensional endfire array with six parasitic side rows;
FIGURE 3 is an end view of a three-dimensional endfire array; and
FIGURE 4 is a schematic representation of an arrangement for rendering the parasitic arrays suitable for scatter propagation.
The end of an array may be considered to be a 3,096,520 Patented Jul 2, 1963 radiating aperture, and, because there are no physical -may be accomplished by changing the width of the virtual aperture and the amplitude and phase distribution within said aperture. An array change from single to two-dimensional allows an increase in gain by increasing the virtual aperture; reducing side lobes by changing amplitude and phase distribution within said aperture; and simultaneously increasing gain and achieving side lobe reduction by changing both aperture distribution and width.
Referring to FIGURE 1, a ground plane 10 may be used, although it does not form a necessary part of my invention. Mounted on the ground plane 10 is :an example of an endfire antenna shown as a Yagi array 11 of monopoles with a reflector 12. A coaxial feed means 13 excites the array from beneath the ground plane.
It was found that the width of, and distribution in the virtual aperture at effective energy levels can be changed in the desired manner by symmetrically placing one or more shorter rows of parasitic elements 14 and -15 V on either side of the center :array. The utilization of a non-symmetrical arrangement produces a change in pattern. Parasitic side rows :14 and 15 act as smaller wave channels fed mainly by coupling from the main center array 11 which results in a two-dimensional parasitic endfire array excited by a single feed 13 of the main array 11.
The dotted line portion represents an aperture plane with arbitrary limits of 20 db of maximum power level in the vertical and transverse directions.
Side rows '14 and 15 are adjusted so that the phase front in the virtual aperture is as uniform as possible and the amplitude distribution is given the form needed for a specified pattern. Phase may be controlled by adjusting the phase velocity which depends on the spacing, height, and diameter of the parasitic elements. An infinite number of combinations of these parameters may be used to achieve a desired phase velocity. Amplitude may be controlled by variation of side row length. The adjustments of the phase front and amplitude distribution can be performed, within limitations, relatively independently of each other.
In order to couple sufiicient energy to the side arrays 14 and 15, the usual placement of these arrays falls within the virtual aperture. The phase deviation in the virtual aperture of the center array 11 without the parasitic side rows undulates and side row placement is usually made at the point of maximum deviation; however, adjustment of the various parameters allows a placement anywhere within the virtual aperture and even slightly outside it depending on the amount of coupling energy desired.
Tests made on the array of FIGURE 1 indicate an increased gain of 30% and an increased virtual aperture of 37% using the following exemplary physical dimensions:
Element diameter .04 8x FIGURE 2 is a top view of an antenna having a center array 11 with reflectors 12, a feed 13 and six side rows 16, 1'7, 18, 119, 20, and 21 wherein the virtual aperture is increased by 66% above the Yagi type endfire array, and the measured gain increase is 60%.
An extension of the principle of this invention to increase the height of the virtual aperture in the vertical direction would be to place side arrays above (and below if there is no ground plane) the center array 11. By thus passing from a two-dimensional to a three-dimensional array a further increase in gain results. FIG- URE 3 is a representation of an end view of a threedimensional antenna having a central Yagi array 11 and parasitic arrays 22, 23, 24 and 25. Of course the absence of a ground plane indicates the use of dipoles rather than monopoles in this embodiment. Since the parasitic arrays do not act as reflectors, the height of the elements of the arrays will be less than a quarter wavelength for monopoles and a half wavelength when dipole elements are used.
Thus, the performance of an endfire array may be explained relative to the concept of a virtual aperture located at the end of the array, and accomplishment of control of this aperture by coupling energy parasitically from the main array into adjacent side rows.
Utilization of the teachings of my invention produce changes in side lobe level and gain, simultaneously. These accomplishments are obtained by low cost antenna construction without an appreciable increase in space compared with conventional endfire arrays of the same length. Furthermore, the initial feed system can be used without complicated power distribution networks common to other antennas capable of producing comparable results.
Non-symmetrical arrangements of the parasitic arrays fall within the scope of my invention in that assymetry produces a change in the pattern of the resutling beam; therefore, it follows that a sweep for scatter propagation may be achieved by changing the phase by changing the height of the parasitic array; e.g., by attaching the 4! monopoles to a single support and moving the elements through the ground plane and controlling the height by means of an eccentric or cam acting on said support. or by rotating the dipoles of the parasitic side rows, which, in effect, change their electrical length.
Although the invention has been described with reference to particular embodiments, it will be understood to those skilled in the art that the invention is capable of a variety of alternative embodiments within the spirit and scope of the appended claims.
1. A method for controlling the side lobe and gain characteristics of an endfire antenna array by controlling the virtual aperture of the array comprising the steps of placing parasitic arrays about said endfire array adjusting the phase distribution in the virtual aperture by varying the height, spacing and diameter of the parasitic elements of said parasitic arrays, and adjusting the amplitude within said virtual aperture by varying parasitic array length.
2. An endfire antenna array comprising a main endfire antenna, and a series of parasitic arrays located symmetrically about said main endfire antenna at points of maximum phase deviation in the virtual aperture of said main endfire antenna.
References Cited in the file of this patent UNITED STATES PATENTS 1,860,123 Yagi May 24, 1932 2,199,050 Jenkins Apr. 30, 1940 FOREIGN PATENTS 399,770 Great Britain Oct. 12, 1933 OTHER REFERENCES Beam Antenna Handbook, by W. I. Orr, copyright 1955, pages 2224 TK 7872 A607.
Silver, 8.: Microwave Antenna Theory and Design, I 1949, published by McGraw-Hill Book Company, Inc.,
New York, N.Y., pages 158, 159, 179, 180.