US2495219A - Directional antenna system - Google Patents

Description

Jan. 24-, c BECK DIRECTIONAL ANTENNA SYSTEM 5 Sheets-Sheet 1 Filed Jan. 24, 1945 S kh h zubkw lNl/E/VTOR By A. c. BECK ATTORNEY Jan. 24, 1950 BECK 2,495,219

DIRECTIONAL ANTENNA SYSTEM Filed Jan. 24, 1945 I5 Sheets-Sheet 2 l l l I l l l I I I now/v up H-PLANE smear/vs PATTERN- SYSTEM or INVENTION //\1 l/ENTOR A. C BECK ATTORNEY 3311- 24, A. c BECK DIRECTIONAL ANTENNA SYSTEM 3 Sheets-Sheet 3 Filed Jan. 24, 1945 30 R/GH T E-PLANE DIRECfll/E PA TTERN- PRIOR ART SYSTEM LEFT LEFT I RIGHT PLANE DIRECTIVE PATTERN *SYSTEM OF wvn/r/o/v /N l/EA/TOR A. C. BECK ATTORNEY Patented Jan. 24, 1950 UNETED sr DIRECTIONAL ANTENNA SYSTEM Alfred 0. Beck, Red Bank, N. la, assignor. to Be l Telephone Laboratories, Incorporated,

New

York. N. Y., a corporation of New York Application January- 24, 1945,. SBrial' No. 574,335,

5Glain 1s. (Cl. Zak-3.3.65)

been found. that, by reasonof the passive or shadow-effector the double guide feed, thedirective pattern. taken in the horizontal lobev switching. plane contains fairly large minor lobes; whichproduce false indications on the cathode ray tube. indicator: associated with the transceiver. Accordingly, it appears desirable toprovide means for eliminating or-reducing these undesired minor lobes. While various arrangements have: been suggested:- heretofore for reducing. undesired minor lobesas, for example, the depressed orv oil?- focusv feed disclosed in Patent. 2,427,005.- granted.

to A. P. King on September 9, 19%7, the prior art arrangements are not entirely suitable for use in. thelobe switching system mentioned above and,. moreover, may cause a. decrease in the antenna. gain. Accordingly, it appears advantageous tov accomplish the minor lobe reduction, in applicantfs lobe switching system, without depressing the feed and in a manner such as to. increase, or at least not. change materially; the antenna gain.

It iszoneobject of: the invention tosecure, in an antenna system, a directive pattern having neg-- ligible minor lobes.

It isanother object of this invention toreduce, in an. antenna. system comprising; a parabolic reflector and. a vertical front dielectric guide feed, the. minor lobes inv the. horizontal plane directive pattern, without decreasing the antenna gain;

It is another objectof this: invention to eliminate; in; a lobe-switching antenna. system. having a double directive pattern, overlapping of the. mai or lobe of one pattern with a minor lobe of the other patter-nor. so-ca-lled false cross-overs, during the lobe switching operation.

In accordance with one embodiment of the-in.- vention a small horizontal flat. metallic deflector is: attached to the double guide feed. of the lobe switchingantenna referred: to above at. a point immediately belowthe. two'guide. apertures. i-he. deflector or window sill is below, and parallel to... theoptical. axis of the. paraboloidal reflector and extends a short distance towards the IBfiEG-r tor. The paraboloidal reflector. extends appr.oxi.-;

mately twice. as: far above its horizontal optical axis as. below. In. transmission, most of the wavecomponents emitted alternately by the two aper...

tures and; propagated. towards the portion of the.-

refiector adjacent. the. lower edge, and most of the.

componentspropagated in. downwardly pointing.

directions which avoid the reflector, are redirected by the deflector upwards towards theover-= hanging upper portion of the parabolic reflector,

and are thence: radiated in a general horizontal direction. Hence the radiation from thelower reflector portion mentioned above, which portion faces the. dual. guide feed, is relatively small; and}. as-compared to that-producedby the lower reflec-' tor section in the original system, greatly decreased; and. most. of the energy is reflected. or.

radiated by the upper portion, including the;-

overhanging section, of the reflector. As aresult, the shadow effect of the guide feed is minimized and the minor lobes in the directive pattern, taken in thehorizontal lobe-switching plane, are: substantially reduced. In reception, the converse operation is obtained by virtue of the reciprocity theorem.

The-invention will be more fully understoodfrom a perusualor the following specificatiom, taken in conjunction with the drawing on which.

like reference characters denote elements of similar function and. on which;

Figs, 1, 2 and 3 illustrate, respectively, a sectional side view, a. sectional f-rontview and. a top ziiewof the preferred: embodiment of the inven- Fig. 4- illustrates, for purpose of. explanation, the directive pattern taken in the E or. horizontal lobe-switching plane, of a prior art. system constructed in accordance with my copending application mentioned above;

Fig. 5 illustrates the- E-plane lobe-switching; directive pattern of the. system of Figs. 1,. 2 and 3.; and:-

Fig. 6 illustrates the H or' vertical plane pattern" of the system of Figs. 1-, 2 and 3;

Referring to-Fi'gs. 1,2 and 3, reference numeral. I denotes. atranslation device, such as a radar transceiver, and. numeral 2. designates a main metallic airefilled vertical dielectric guide connected thereto. The main guide 2 is connected. toa pair of metallic feed guides 3 and 4: through a guide. switch 5- of the finger type disclosed in my copending application mentioned above, or. of.. a different. type, such as, for example, the so.- called "fin type. At the top, each of the teed,

. guides. is bent ninety degrees and contains; an

antenna aperture, the two apertures being inand 1, or window 8. The deflector 9 has a 'circular front edge, Fig. 3, and at its widest portion extends outwardly from the {dual guides 5, I, a'

distance of approximately a half wavelength.

Reference numeral H denotes a concave reflector comprising a paraboloidalisection l2 having an ellipsoid opening and a conical underhang: ing section IS. The section l2 has a horizontal optical or principal geometricalaxis I4 exten d ing above'deflector' e, the two 'latus' rctums l and I6 and a point-focus !1.- The focus I! is po- Isitioned in'the plane of, and approximately midway between, apertures 5 and l, and the optical axis l4 passes through the point focus l1 and the vertex of the reflector i l In. Fig. -1, the dot-dash curve 18 illustrates the parabola which is re} volved about axis !4 to secure the paraboloidal contour of section l2. If desired, the underhanging section, instead of being coniform, may be barrel-shape, which shape is obtained by revolvin'gthe bottom edge IQ of the paraboloidal reflector section I2 counter-clockwise, Fig. I, through a small angle and about the latus rectum IS. The conical or barrel feature forms no part of the present invention, and, if desired, the underhanging section I3 may comprise merely an extension of the paraboloidal section [2.

. Considering the vertical plane, Fig. 1, containing axis i l and the point-focus H, the line 20 perpendicular to axis i 4 represents, for purpose of explanation and comparison, the diameter or opening of a conventinal paraboloidal reflector similar to' that included in the system of my above-mentioned patent. The conventional reflector just mentioned extends the same distance above and below the axis l4. In contrast, the concave reflector ll" of the present invention extends about twice as far above as below axis M. In Fig. 1, the vertical heights of the portions of reflector ll above and below the axis M are designated by the reference letters B and A, respec- 'tively; In one embodiment tested at a design wavelength of about 9,8 centimeters, B and A are 11 and'5inches, respectively, and in another embodiment tested at the same wavelength, B and A are'2 feet and 1 foot, respectively. In the lastmentioned embodiment, the horizontal width of the reflector ll, taken along the-latus rectum I6, is 5 feet. Hence, the concave'reflector ii of the present invention'com'prises an overhanging or canopied portion 2! having a vertical dimension- C," and, in the vertical plane containing axis I4 and point-focus H, the reflector aperture 22 is tilted forward and forms an acute angle with the axis M. As will be explained in detail below, the

reflective canopy 2i and the reflective window sill 9 mutually cooperate and function to eliminate the shadow effect of the dual guides 3, 4, and, consequently, to reduce the undesired minor lobes.

Preferably, but not necessarily, the paraboloidal section I2 is of the so-called dielectric guide grid or'grille type, as illustrated, instead of the solid type; and the underhanging section 13 is of the solid type. The grid reflector l2 comprises horizontal metallic strips 23, which form the guide openings 24 and are spaced, on centers and vertically, a distance V of about one inch, corresponding to less than a half wavelength. The strips have a depth D, Fig. 1, of about one inch and are supported by the transverse members 25 and the rim member 26, the members 25 and 25 being made of conductive or non-conductive material. The reflector is designed for use with waves polarized horizontally, as shown by arrow 21, Fig. 2. Hence, the transverse members 25,

and the waves, which without deflector 9 would which appear to be vertical as seen from the dual The general 'transceiving and lobe-switchingv operation of the system of Figs. 1, 2, and 3, is basically the same as that of the system of my above-mentioned patent. Briefly, in transmis-: sion, horizontally polarized waves are suppliedv by device I to main guide 2 and through the guideswitch 5, alternately, to the dual feed guides 3 and 4. The waves are alternately emitted'b the antenna apertures 63, 1, and are reflected primarily.

in a horizontal direction by theconcave reflector ll. representative direction or path followed'by' a wave component emitted from one of apertures 5- or 1, towards the upper portion of reflector H and redirected thereby. When the waves are.

emitted by the left-hand antenna aperture 5,-

maximum action in the horizontal plane occurs in the direction 29, Fig. 3, lying on the right side, of," and making an acute angle with, the optical axis l4; and when the waves are emitted by the right. antenna aperture I, the direction 36 of maxi-;

mum action is on the left side of optical axis i4 and forms therewith an acute angle.

the principal axes of the left and right'1obeswitching main beams or major lobe patterns;

In recep-- taken in the horizontal or E-plane tion, the converse operation is obtained.

In more detail, the E-plane pattern of the left;

or'right main beam is relatively narrow by reason of the parabolic contour in this plane of the con-" cave reflector; and the H-p1ane pattern of the main beam is somewhat wider, so that a fanbeam .is secured. Assuming, for the moment, that the deflector 9 is omitted, the underhanging reflector section !3 functions to increase the radio action at the high 'or sky angles included in the 50-70 degree vertical sector. With deflector 9 in place, in accordance with the invention, some of the waves propagated from aperturet or i in downwardly pointing directions, such as direction 3| which avoids the reflector l I altogether, or direction 32 which is intercepted by the bottom portion of the underhan'ging reflector section l3, are redirected by the deflector 9 towards the upper part, particularly the overhanging part 2 i, of the concave reflector H, as shown by arrows and 34. The deflected waves are then propagated horizontally as shown by arrows 35 and 36. sequently, as compared to the prior art system of my above-mentioned patent, the intensity of the radiation from the bottom reflector-portion facing the vertical dual feed guide is decreased In Fig. 1, reference numeral 28 denotes a;

The direc-. tions 29 and 30 of maximum action correspond to- Con-- be radiated from this reflector portion, are in a sense transferred to and reflected by the overhanging reflector portion 2|. As a result, the passive action or shadow effect of the dual guide structure 3, 4, which causes the beam to split into minor lobes, is reduced. Also, the horizontal or E-plane of maximum action is, in effect, no longer coincident with the horizontal plane containing the optical axis l4 of the concave reflector, and an E-plane directive pattern with reduced or negligible minor lobes is secured. In the vertical or H-plane, the deflector renders the high angle or sky radiation less than that obtained in the above-mentioned prior art system.

Referring to Figs. 4 and 5, reference numerals 31 and 38 denote, respectively, the alternate left and right measured E-plane directive patterns obtained for the lobe-switching prior art antenna system of my patent; and numerals 39 and 49 designate, respectively, the alternate left and right measured E-plane directive patterns obtained for the lobe-switching antenna system of Figs. 1, 2, and 3. In Fig. 4, the left pattern 31 includes a major lobe 4 I, first dips or nulls 42, first minor lobes 43, and higher order minor lobes 44; and the right pattern 38 includes a major lobe 45, dips 46, first minor lobes 41, and high order minor lobes 48. In Fig. 5, the left pattern 39 includes a major lobe 49, the right first null 50, the right first minor lobe 5|, and the higher order minor lobes 52; and the right pattern 49 includes the major lobe 53, the left dip 54, the left first minor lobe 55, and the higher order minor lobes 56. The half power width of each major lobe 4!, 45, 49, and 53, is denoted by the reference numeral 51 and the real or desired cross-over points of patterns 31 and 38, and patterns 39 and 40, are denoted by numeral 58.

As shown in Fig. 5, the half power width 51 of each of major lobes 49 and 53 is relatively small. The first minor lobes 5| and 55, Fig. 5, are only about 12 to 15 per cent of the major lobes 49 and 53, respectively, and therefore negligible. By

way of contrast, the first minor lobes 43 and 41, Fig. 4, are about 35 per cent of the major lobes 4f and 45, respectively. Also, the higher order minor lobes 52 and 56, for the system of the in- .vention, are considerably lower than the correspbnding higher order minor lobes 44 and 48, for the. prior art system. It will be noted that the left first minor lobes 43 and 41, Fig. 4, of the two Hence, an indication resulting from terns 39 and 40, Fig. 5, are at about the 12 per cent power-point and the indications produced thereby are therefore negligible.

Referring to Fig. 6, reference numeral 6| denotes the vertical plane directive pattern for the system of Figs. 1, 2, and 3. The pattern includes the major lobe 62, the dip 63, and the higher angle or sky minor lobe 64. The half power width 65 of the major lobe 62, it will be noted, is greater than the corresponding width 51, of the major lobes 49 or 53, for the system of Figs. 1, 2, and 3. If deflector 9 were omitted, the minor lobe 64 would be considerably higher.

Thus, in accordance with the invention, the minor lobes produced in a lobe switching system are reduced. The gain of a system constructed in accordance with the invention and comparable in size to a system constructed in accordance with my patent is 19.8 decibels, whereas the gain of the comparable system of my copending application is about 19 decibels so that the lobe reduction is secured with a slight increase in gain.

Although the invention has been described in connection with a specific embodiment, it is not to be limited to the embodiment described, inasmuch as other apparatus may be employed in successfully practicing the invention.

What is claimed is:

1. In combination, a reflector having an optical or principal geometrical axis and a focus said reflector having a concave surface on one side of said axis, a primary antenna at said focus and a flat deflector extending parallel to and lying on the opposite side of said axis, said deflector being spaced from said reflector and positioned sub stantially between said reflector and said primary antenna.

2. A combination in accordance with claim 1, said axis being substantially horizontal, said reflector extending approximately twice as far above as below said axis and said deflector being positioned below said axis.

3. In combination, a paraboloidal reflector having a substantially horizontal optical axis, said reflector extending farther above than below said axis, a vertical dielectric guide extending across the lower part of said reflector and having an antenna aperture facing said reflector, and a plane deflector attached to said guide, said deector being positioned entirely below said axis and extending towards said reflector.

4. In combination, a concave reflector having a focus and a substantially horizontal optical or principal geometrical axis, said reflector extending farther above than below said axis, a pair of vertical wave guides positioned in front of said reflector and each having an aperture facing said reflector, the reflector focus being midway between said apertures, a horizontal plane deflector attached to said guides and extending below said axis and towards said reflector, a wave guide switch, a radar transceiver, said guides being connected through said switch to said radar transceiver.

5. A combination in accordance with claim 4, said reflector comprising a plurality of wave guide openings dimensioned to reject or reflect wave components, the upper and greater portion of said reflector having a 'paraboloidal contour and the imaller and lower portion having a conical conour.

ALFRED C. BECK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,912,487 Matera June 6, 1933 1,934,078 Ludenia Nov. '7, 1933 2,002,181 Ilberg May 21, 1935 2,026,652 Ponte Jan. '7, 1936 2,350,664 Alexander June 6, 1944 2,396,044 Fox Mar. 5, 1946 2,422,184 Cutler June 17, 1947 2,427,005 King Sept. 9, 1947 FOREIGN PATENTS Number Country Date 668,231 Germany Nov. 28, 1938

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