US2598005A - High-gain directionalized antenna - Google Patents

Description

May 27, 1952 Filed Jan. 13, 1950 GAIN IN DB COMPARED TO REFERENCE DIPOLE K. H. LlPPlTT 2,598,005

HIGH-GAIN DIRECTIONAL-IZED ANTENNA 2 SHEETSSHEET 2 Tic]. '3.

CHANNEL 8? MEGACVCLES FREQUENCY IN INVENTOR.

Byway? ,9 T TOP/V5 V Patented May 27, 1 952 HIGH-GAIN DIRECTIONALIZED ANTENNA Kendrick H. Lippitt, Earlville, N. Y.,assignor to Technical Appliance Corporation, 'Sherburne, N. Y., a corporation of New York Application January 13, 1950, Serial No. 138,356

1 Claim. 1

This invention relates to directionalized antennas, and more particularly to antennas for operation at ultra-high-frequencies.

A principal object of the invention is to provide a directionalized antenna of the Yagi type, and particularly useful in television systems and the like.

Another object is to provide an improved directionalized antenna array of the kind employing one or more director elements.

Another object is to provide an improved antenna of the Yagi type.

A feature of the invention relates to an antenna array of the Yagi type, wherein at least one of the director elements is driven or connected to the feeder or transmission line which also excites the main antenna element of the array.

Another feature relates to an antenna array of the Yagi type, wherein at least one of the director elements is connected physically in circuit with the main antenna element whereby optimum current-phase relations can be obtained throughout the various elements of the Yagi array, while maintaining the desired directional sensitivity and gain characteristics of the Yagi antenna.

A further feature relates to an improved antenna of the Yagi kind, which has a much higher operating impedancethan the conventional Yagi array. As a result of this feature, it is possible to use either one or more stacked arrays of Yagi units, while permitting an impedance match to a high impedance feeder line, such for example as the standard 300-ohm wave transmission line.

A still further feature relates to the novel organization, arrangement and relative location and interconnection of parts which cooperate to provide an improved antenna of the Yagi type.

In the drawing,

Fig. 1 is a perspective view of an antenna array embodying features of the invention.

Fig. 2 is a top-plan view of Fig. 1.

Figs. 3 and 4 are respective coordinate and polar graphs explanatory of the operation of the antenna array of Figs. 1 and 2.

As is well-known in the antenna art, the Yagi antenna comprises a main antenna element in the rear of which is mounted a reflector which is electrically floating and adjusted in length, and spaced from the main element a distance of between .1 and .27\, where A is the wavelength of the radiation to be transmitted or received by the antenna. The conventional Yagi antenna also has a series of director elements mountedin front of the main antenna element, these director elements electrically floating so as to be parasitically excited from the main antenna element. For a detailed description of such a typical Yagi antenna, reference may be had to.Radio Engineers Handbook by F. E. Terman, First Edition, pages 811 and 812, published by McGraw-Hill Book Company, Inc., New York, 1943.. While such Yagi antennas have pronounced. directional characteristics'because of the spacing and parasitic excitation of the reflector and directors, the antenna array as a whole has an operating impedance of extremely low value, for example of the order of 15 ohms. On the other hand, in certain installations, for example in television systems, it is desirable to use a feeder or wave transmission line of relatively high characteristic impedance, for example 300 ohms, and still be able to maintain an impedance match between theantenna and transmission line without.using complicated impedance matching networks This problem of impedance matching to the feeder or line. In such a case the parallel connection renders the operating impedance of the Yagi array even smaller, and depending upon the number of bays in the stacked array.

According to the present invention, it is' possible to provide a Yagi antenna having the desired directional features, while providing the antenna with a characteristic impedance upwards of 250 ohms. In fact, it is possible to provide an impedance approximating 600 ohms, so' that two such arrays can be stacked and connected in parallel to a common feeder line.

Referring to the drawing which shows a two stack array, each array, according to the invention, comprises a main antenna element 1 0, preferably, although not necessarily, inthe form of a. folded dipole-comprising spaced horizontal legs I I, I2, directly united at their opposite ends by the end sections l3, I4. The lower leg I2 is discontinuous at its center and is fastened by suitable bolts [5, to an insulator strip or block Hi. This block I6 also has fastened thereto a U-shaped metal bracket I! having lateral lugs which are adapted to be fastened, for example by bolts 18, to a metal bar or strip l 9, and with the center-of leg II also clamped'therebetween. Bracket'll is 20, which in turn is fastened in any suitable manner'to a tubularmetal mast 2|. This fastening may comprise, for example, a horizontal chanv neled member 22, and a vertically channeled member 23, respectively clamped to each other and to the members 20, 2i, by suitable screws or bolts (not shown) Mounted on the cross arm 20, in spaced relation to element I0, is an adjustable parasitically excited reflector, comprising for example a pair of overlapping metal rods 24, 25. These rods may be anchored to the flattened end 28 of arm by suitable screws 21, and are preferably bound by a pair of metal bands 28, 29, to hold them together as a unit. Mounted in front of the main element In is a first director elements 30, preferably, although not necessarily, in the.

form of a folded dipole having the spaced legs 3!, 32, with integral end sections 33, 34. This director can be adjustably attached to the cross arm 20 by a U-shaped metal bracket and clamping plate 36 located at the center of the leg- 3l,.tlie bracket 35 being also. fastened to the cross: arm: 20 by suitable. screws (not shown). The bracket 35 carries anr insulator strip 37.. to which the. central gapped ends of the leg 32 are fastened by suitable bolts 38'. Attached to the arm 2|)v infront of the director 30, is another director 39 which may comprise a. pairof overlapped metal. rods4li, ii, similar to rods 24 and 25, and similarly attached to the arm 26.

Themain element H] has a physical length 2 equal to approximately A/Z. Preferably also, the-director 30 has approximately the. same length esthe main element 2%. The reflector is: spaced; from themain antenna element a distance s. between 0.1x and 025i. rector 30'is spaced from the main antenna element Ill a distance 31 equal to approximately 012A, and the second director as is spaced from the first director 33 approximately 0.1x. It will be understood, of course, that these particular. spacings are not critical, and can be adjusted within. substantial ranges, depending upon the impedance that is desired. In any event,- the spacing between each adjacent pair of. elements should be substantially less than 0.25A...,,Als0 mounted beneath the. above-mentioned'array is a similar array ilandfurther detailed description thereof is not. required. Preferably however, the vertical spacing s; between the two stacked arrays in approximately 0.5%.. It. will be understood, of course, in order that the mast 2l and the cross arm 28 may be of metal, all the elements, are attached at their centers or voltage nodal points to the respective crossarm, and preferably all the elements of each array are mounted on a common plane, and with the elements of one array in planar alignment with the correspondin elements of the other array.

In accordance with one feature of the invention, the gapped ends of the main element In are'connected to the corresponding gapped ends of the director 30 by wave transmission line section 43 having an electrical length equal to ,12A, and having a characteristic impedance equal to 300. ohms. The bolts l6 and 38 may be used as binding posts for this connection. Also connected to the gapped ends of the leg l2, are two vertically-extending spaced parallel metal rods 45, 46. These rods at their lower ends are likewise connected to the gapped ends of the main antenna element 41, and through the two-wire transmission line section 48, to the corresponding gapped ends of the director 49. The rods 45 andflfare held in. fi'xed predetermined spaced.

transformers between the two stacked units of the array. A suitable radio set, either transmitter or receiver 53, is connected to posts 5| by a teeder or transmission line 54 of the proper characteristic impedance to avoid the setting-up of standing waves thereon.

From the foregoing, it will be seen that the directors 34 and 49, instead of being parasitically excited, areconnected to the same feed line 54 to which. themain elements Ill and 41 are connected. I have found that by this arrangement it is possible to employ for the line 54, one which has a, high characteristic impedance, for example as high as 300 ohms, and it ispossibleto adjust the elements of each Yagi array so'that.

each respectively has a characteristicv impedance of approximately 300 ohmaso'that by using )\/4 transformers from each array to the. block 50, the combined impedance at the points; 51' is. It will be understood.

approximately 300 ohms. of course, that. the invention is, not. limited. to any particular adjustment or characteristic impedance, since in any event a much greaterimpedance oanbe obtained when the director 58 and the main element iii are physically connected to the same transmission line or feeder, ascompared with the conventional Yagi. arrangement, where the director is merely parasitically excited. In order to understand how thisis effected, it should be noted that when the conventional parasitic director element is placed 0.1x from the-element Hi, a considerable change is eifected in the input impedance of element :8, because of the space inductive transformerlike action between it and the parasitic element. It is this reaction which reduces the: operating impedance of a conventional Yagi system. to. an extremely low value. The twin-driven main and director array according to the invention, is:

not affected by this conventional parasitic coupling condition, because the main elementfeeds the first director through the impedance-match.- ing line 43, whose length is approximately 0.12s, and in any event is less than 1125A.

In one particular antenna array that wasv found to be highly efiicient. in the allottedtelevision inches; the director 36 had an end-to-endlength of approximately QO-inches with a spacing between the legs 3l, 32, of approximately three and one-quarter. inches; the parasitic refiectorM-ZS had a length of approximately 92' inches; the

parasitic director 39. had a length of approximately 78 inches; the spacing s between the main element and the parasitic reflector was approxi-- mately 33 and one-half inches; the: spacing. s1 between the driven director 36: and the main element- H] was approximately 20 inches; the spacing s2 between the parasitic director 39 and the driven director 38 was approximately 17 inches;- and the spacing s3 between theupper array and the lower array 42 was approximatelyQOinches.

It will be understood, of course, that the inven-= tion is not limited to the particular dimensions and impedance relations above mentioned, as will be clear to those familiar with the antenna art. However the driven director 39 and the parasitic director 404l are preferably chosen of such a length that the reactance imposed upon the main element [0 by the space inductive coupling or transformer-like coupling between the various elements, is a conjugate of the reactance at the driving point produced by the reflector system.

Likewise, the invention is not limited to the use of a plurality of stacked Yagi arrays, since desirable directional and gain characteristics are obtained with a single Yagi-array. Furthermore, while the drawing shows 'a-j sing l e parasitic director in front of the driven director 39, it will be understood that more than'one such parasitic director may be employed.

Fig. 3 is a graph showing the relation between the operating frequency in megacycles, and the gain in decibels, compared to a standard or reference dipole. The dotted-line graph 55 in Fig. 3 represents the characteristics of a single array such as shown in the upper portion of Fig. 1.

The full-line graph 56 represents the relation between operating frequency and decibel gain, where a two-bay stacked array such as shown in Fig. 1 is employed.

Fig. 4 shows the corresponding polar field pattern diagram under these two conditions; the L dotted-line graph 5! representing the single array, and the full-line graph 58 representing the two-bay stacked array of Fig. 1.

While certain specific embodiments and dimensions have been referred to herein, it will be understood that the invention is not limited thereto, and that various changes and modifications may be made therein coming with the purview of the appended claim.

What is claimed is:

In an antenna array of the Yagi type? the combination of a main antenna element, a parasitic reflector element, a series of director elements, and a feeder line connected in parallel REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,283,914 Carter May 26, 1942 2,297,329 Scheldorf Sept. 29, 1942 2,474,480 Kearse June 28, 1949 OTHER REFERENCES Radio Engineers Handbook by Terman, 1st ed., published 1943, pages 811-812.

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