US2540757A - Antenna - Google Patents

Description

H. J. RIBLET Feb. 6, 1951 ANTENNA Filed June 16, 1944 FIG-6 INVENTOR.

HENRY J R/BL E7 Mia-9A4 Patented Feb. 6, 1951 Tam OFFICE ANTENNA 'Henry J. Riblet, Cambrid mesne assignments,

America as represented b go, Mass, assignor, by

the United States of y the Secretary of War Application June 16, 1944, Serial No. 540,611

2 Claims. (Cl. 250-33.65)

tion pattern, the pattern being narrow in azimuth as well as elevation. As is well known, a pillbox type reflector utilizes a metallic reflecting parabolic cylinder (or another reflector of suitable shape), the parabolic surface thereof usually being used relied upon to narrow the radiation pattern in the elevational coordinate. Plane parallel metallic walls enclose the ends of the parabolic cylinder, the walls cooperating to give a directional characteristic to the pattern in the azimuth coordinate. If desired, the device may be rotated through 90 whereupon the parabolic cylinder narrows the radiation in azimuth, and the walls in elevation.

A reflector of this character may be excited in various ways, one example being by a wave guide terminating in a horn disposed on the focal axis of the parabolic cylinder. Suitable dipoles or other means may be used for this purpose, if desired. As mentioned, the radiation pattern obtained by a pillbox antenna of this character is highly directional both in azimuth and-elevation.

The present invention utilizes this pillboX type reflector to provide an antenna having a relatively wide and generally uniform radiation pattern in one coordinate, usually azimuth, the pattern being substantially free of objectionable side lobes. This unexpected result may be obtained by modifying the highly directional effect of the plane parallel walls of the reflector. This modification is effected by the use of two diverging plane metallic members, hereinafter called flaps, extendin from the reflector walls, one on each side of the reflector mouth. As will be understood, the reflector mouth is the open side of the reflector from which radiations emanate into free space. Theseflaps constitute a continuation of the usual walls of the reflector, the width of the flaps in the direction of radiation having a substantial value such as three oriou'r wave lengths of the frequency used. As mentioned, a substantial range of uniform azimuth coverage is obtained through the use of suchflaps vational view flaps disposed It has been found that a relationship exists between the angle enclosed by the diverging metallic flaps and the range in azimuth over which the radiation is substantially uniform. Ingeneral, the greater the angle defined by the flaps, the greater is the uniform range in azimuth.

In all instances of angular relation between flaps (0 to it is possible to obtain desirable results with the flaps joined to the reflector in the plane of the reflector month. However, it has been found herein that improved uniformity of azimuth response (and sharper cut-oft at the desired limits of the range) may be obtained by backsetting the flaps somewhat in relation to the plane of the mouth. The distance the flaps are baclrset depends to a large extent upon the angle enclosed by the flaps. In general, the smaller the angle between flaps, the greater the distance between the plane of the reflector mouth andthe points on the reflector walls where the flaps are attached.

When the flaps are disposed at an angle of 180 with each other (the angle for maximum azimuth range), most uniform azimuth response and sharpest cutoff are obtained when the flaps are disposed in the plane of the reflector mouth. That is, the flaps are not backset, but rather they are attached to the ends of the reflector walls.

It has been stated that a pillbox type reflector provided with diverging flaps radiates a substantially uniform pattern over a predetermined azimuth range. However, minor variations in, in-

tensity do exist, although the mean radiation pattern coincides closely with the segment of a circle having its center at the antenna, the segmerit being defined by the angle of predetermined azimuth range. If desired, these minor variations in intensity may be substantially eliminated by curving the extremities of he flap at an increasing rate of curvature as the flap ends are approached. The application of such curved ends to flaps of this character and a discussion of the operation of such curved ends are disclosedin the patent to Gerald L. Tawney, No. 2,469,419. As mentioned, the use of curved flaps tends to smooth out minor variations in intensity with the result that the radiation pattern is substantially circular over the azimuth range.

In the drawing, l is a side 'elevational view of a pillbcx type reflector having flaps disposed at an angle cf less than 180 with each other; Fig. 2 is a sectional View on the line 2-2 of Fig. 1 'showing in somewhat diagrammatic fashion the radia tion pattern of the antenna; Fig. 3 is a side eleof a pillbox type reflector having at an angle of 180 with each other;

guide 23 and the axis of the of azimuth coverage r Fig. 4 is a sectional view on the line 4-4 of Fig. 3,

and showing, similarly to Fig. 2, a radiation pat tern; Fig. 5 is a side elevational view of a reflector having 180 flaps, the flaps being terminated in a gradually increasing curve and Fig. 6 is a sectional view on the line 6-6 of Fig. 5.

Referring to Figs. 1 and-2, a pillbox type reflector may comprise a metallic semi-parabolic cylinder l having its ends closed by parallel metallic end walls I l and I2. As will be understood, the use of a semi-parabolic reflector is merely exemplary and, if desired, the more usual symmetrical parabolic cylinder may be used. The width of cylinder I0 is generally small as compared to the wave length used with the reflector, a width of one-third wave length being a satisfactory value in this instance. A metallic bottom closure l3 lying generally along or parallel to the axis of the parabola is suitably associated with cylinder l0 and walls H and i2, as shown in Fig. 1.

A base member i is rigidly closure H3 in any suitable manner, as

secured to bottom by bolts H5.

tion pattern between the amount the flap-s are backset from the mouth and the angle enclosed by the diverging flaps. In general, this relationship is an inverse one; the smaller the angle between flaps, the greater is the value of setback.

A reflector supporting structure H has an enlarged top portion i8 rigidly secured to member 1'5. Supporting structure ii is adapted to support the reflector in a suitable radiating position.

The reflector may be excited in any desired manner, one example being by a wave guide rigidly fixed to member :5 as by a bracket 2!. Wave guide it may be terminated in a flared horn 22, the dimensions of the horn and the angular relationship between the axis of wave parabola being ,determined'in accordance with practice well known in the art. In general, the radiating aperture of horn 22 lies on the focal axis of the parabolic cylinder whereby radiations from the aperture are reflected from the cylinder along substan tially parallel paths; Wave guide 20extends from any suitable source of high frequency energy.

The reflector mouth is defined by open ends 25 and 20 (Fig. 2) of end walls H and i2, respectively. Plane metalliciflaps -27 and ZS-are rigidly fixed to end walis IE and i2, respectively, a plurality of angle brackets 20 being conveniently used to-suppert the flaps inmositicn. As show-n 'inthe drawing, flaps 2'! andf28 are vertically substantially co-extensive with end walls H and t2, the vertical planes of 'an'associated wall and flap, 'such'as wall 6 l and flap 2i, being at a horizontal angle with each other. 'Flapszl and 28 extend symmetrically from their respective associated end walls, the horizontal angle between flaps having a value determined by presently to be described considerations. For best results-the flaps should have substantial width in the direction of radiation from the reflector mouth, a value of three or four wave lengths of the frequency used being satisfactory.

As mentioned above, the use :of flaps at the reflector mouth has the effect of increasing the angular range of radiation in one coordinate, in this case the horizontal or azimuth coordinate. It has been found that the range *of effective azimuth coverage is generally proportional to the angle "enclosed by the diverging flaps 2i and 28. Thus, for example, if the enclosed angle is relatively small, such as 40, the range of azimuth coverage is likewise small, while if the enclesed angle is relatively large, such as 150, the range is correspondingly large. In order to obtain a substantially uniform coverage .of a predetermined range in azimuth,

l claimed The somewhat diagrammatic radiation pattern of Fig. 2 shows in full line 30 the approximate energy distribution of the antenna. It will be seen that minor variations in field strength along the line 3| do exist, although the mean pattern of radiation, shown in dotted line 32, substantiallycoincides with a circular segment having its center at the antenna. With certain hereinafter described modifications of the flaps, the actual radiation pattern may be made to coincide closely with dotted iine 32.

Referring now to Figs. 3 and 4 wherein parts thereof also shown in Figs. 1 and 2 bear similar reference numbers, a pillbox type reflector is provided with plane metallic flaps 35 and 36. Flaps 35 and :36 may be secured to end walls ll and i2 respectively by a plurality of angle brackets 3.1. The reflector supporting structure and means for exciting the reflector are not shown, although it will be understood that such members may correspond to thosedescribed above.

The principal characteristic of the embodiment shown in Figs. 3 and 4 is the angular relationship between the diverging flaps ,35 and '36. In this instance, the angle between flaps is this angle being chosento provide a maximum range of substantially uniform energy distribution in azimuth. As shown in Fig. 4, optimum uniformity in azimuth is obtained when flaps 35 and 36 lie generally in the plane of the reflector mouth, i. e. the flaps are'not backset as described above in connection with flaps enclosing angles of less than 180. The radiation pattern 38 is substantially uniform, although minor variations shown at 39 .do exist. Here again, the mean radiation patternshown in dotted line 40 is circular.

Figs. *5 and 6,- wherein like reference numerals for like par-ts are used, show .a pillboxv typereflector provided with flaps .45 and 40 disposed at 180 with each other. In this instance, flaps 65 and 46 have their extremities 4'5 and .40, respectively, curved, the rate of curvature preferably increasing as the flapends are approached. The curves generally may have an exponential form. Such curved extremities ,provide an improved match for transferring energy between the antenn-a "and free space with the result that the above-mentioned-minor variations in energy distribution are substantially eliminated. The radiationpattern 49 thus is substantially circluar. It will be understood that the same desirable result may be obtainediby providing curved extremities on flapsdisposed at other angles witheach other. Use of such curved flaps is disclosed and in .the above-mentioned co-pending application.

Having thus described the invention, what I claim .as new and desire to secure by Letters Ratent is:

.1. ,A reflector type antenna including a source :of-radio-frequency wave. energy, a reflectingcylinder adapted to narrow .r-eflected'radiations in one coordinate, plane parallel walls enclosing the ends of said cylinder and spaced a fraction of the wavelength of said energy to narrow reflected radiations in the second coordinate of a two coordinate system, the ends of said walls defining an open mouth of said cylinder said source being disposed in operative relationship with said re flecting cylinder, and metallic flaps associated with said walls and extending symmetrically and at an acute angle with each other from said walls, said flaps having a width away from said walls corresponding generally to several wave lengths of the radio frequency used, whereby radiations from said antenna are generally uniform over a substantial range in said second coordinate, the actual range provided being a function of the angle enclosed by said flaps, said flaps being backset on said Walls with respect to said reflector mouth, the distance of backset for a given size of reflecting cylinder being generally inversely proportional to the angle enclosed by said flaps.

2. A reflector type antenna including a source of radio frequency wave energy, a reflecting cylinder having an open mouth adapted to narrow reflected radiation in one coordinate, plane parallel walls enclosing the ends of said cylinder and spaced a fraction of the wavelength of said energy to narrow reflected radiation in the second coordinate of a two coordinate system, said source being disposed in operative relationship with said reflecting cylinder, and metallic flaps extending from said walls symmetrically and at acute angle generally uniform over a substantial range of said second coordinate.

The following references e of this patent:

HENRY J. RIBLET.

REFERENCES CITED are of record in the UNITED STATES PATENTS Number Number Name Date Wolff July 2, 1940 Barrow Aug. 26, 1941 Kraus Jan. 20, 1942 Peterson Jan. 27, 1942 Lindenblad Apr. 28, 1942 King May 26, 1942 Peterson June 23, 1942 Johnson et al Dec. .30, 1947 Tawney May 10, 1949 FOREIGN PATENTS Country Date Great Britain Dec. 27, 1928 France July 12, 1943

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