US2434253A - Directive centimetric antenna - Google Patents

Description

Jan. 13, 1948. A. c. BECK DIRECTIVE CENTIMETRIC ANTENNA Filed Aug. 21, 194:5 4 Sheets-Sheet 1 TRANSCEIVER CEIVER.

ELECTRIC PLANE MAGNET/C PLANE I I I I DIRECTIVE CHARACTER/S TIC FOR SYSTEM INVENTOR ATTORNEY Jan. 13, 1948. A. c. BECK 2,434,253

DIRECTIVE CENTIMETRIC ANTENNA Fil'e'ci Aug. 21, 194:5 4 Sheets-Shet 2 5 a r 42 a '1 i 39 40 +omscr1o- 0IREC7'ION 4/ I 43 TRANSCEIVER IN 5 N TOR ,4.c. BECK ATTORNEY Jan. 13, 1948. A. c. BECK 2,434,253

DIRECTIVE CENTIMETRIC ANTENNA 'Filed Aug. 21, 1943 4 Sheets-Sheet 3 RELA IVE. FIE/:5-

1 Jr 1 I I 1 I 1 I +30" +56 +10 -aoa b- DIRECTIVE CHARACTER/ST]: FOR JITSTE OFF/6.0

INVENTOR A. C. BE Ck Jan. 13, 1948. A. c. BECK DIRECTIVE CENTIMETRIC ANTENNA 4 Sheets-Sheet 4 Filed Aug. 21, 1943 TRANSCEIVER TRANSCf/VER rl m u E PLANE E m M DIRECTIVE CHIRACTERISTIC FOR SN'TEM 0F FIGJO WITH VANE OFF/6.10 WITHOUT VANE lNl EN TOR ATTORNEY Patented Jan. 13, 1948 DIRECTIVE CENTIMETBIC ANTENNA Alfred C. Beck, Red Bank, N. J., assignor to Bell Telephone Laboratories, Incorporated,

New

York, N. Y., a corporation of New York Application August 21, 1943, Serial No. 499,453

16 Claims. (Cl. 250-11) This invention relates to directive radio systems and particularly to directive antennas especially adapted for use in centimetric radar systems.

As is known, centimetric and decimetric waves having a wavelength, respectively, of one to ten centimeters and ten to one hundred centimeters are now being used in radio directional and ranging (radar) systems. For waves of these microwave wavelengths the conventional prior art dipole-parabolic reflector antennas used with longer wavelengths are not satisfactory, and it appears advantageous to obtain for use with microwaves more eficient antennas. More particularly, it now appears desirable to secure lobe switching radar antennas having a high gain and negligible minor lobes and lobe sweeping antennas having a sharp major lobe in the electric and magnetic planes.

It is one object of this invention to secure a highly directive microwave radar antenna.

It is another object of this invention to obtain highly efficient lobe switching centimetric antennas and lobe sweeping centimetric antennas.

It is still another object of this invention to energize efficiently the entire line focus of a cylindrical parabolic reflector.

It is a further object of this invention to obtain a highly efficient radar antenna having narrow electric and magnetic plane lobes.

In accordance with one embodiment of the invention, the linear broadside slot antenna of a leaky wave guide of the first kind is aligned with the focal line of a parabolic reflector, the slot antenna and the focal line having equal lengths. In accordance with another embodiment, a linear broadside slot antenna is positioned parallel to the focal line of a parabolic reflector and oscillated through a given angle for the purpose of obtaining a sweeping lobe. In accordance with still another embodiment, the focal line of a cylindrical parabolic reflector is positioned parallel to, and included between, two linear aperture wave guide antennas, and a transceiver is connected alternately to the antennas whereby lobe switching is secured.

The above and other embodiments of the invention will be more fully understood from a perusal of the following specification taken in conjunction with the drawing on which like reference characters denote elements of similar function and on which:

Fig. 1 is a perspective view of a directive antenna constructed in accordance with the invention and Fig. 2 illustrates the measured directive characteristic for the antenna of Fig. 1;

Fig. 3 is a perspective view of another directive antenna of the invention and Fig. 4 illustrates the measured directive characteristic for the embodiment of Fig. 3;

Fig. 5 is a perspective view and Fig. 6 a diagrammatic sectional view of a lobe switching 'sweeping antenna of the invention and Figs. 11

and 12 are measured directive characteristics used in explaining the embodiment of Fig. 10;

Fig. 13 is a perspective view of a different em-- bodiment of the invention for securing lobe sweeping action.

Referring to Fig. 1, reference numerals l and 2 denote, respectively, a transceiver and a coaxial line connected thereto, the line having an outer conductor 3 and an inner conductor 4. Numeral 5 designates a V leaky wave guide antenna comprising the branch wave guides or legs 6 and l and the stem or main wave guide section '8. Each branch guide contains a longitudinal slot antenna 9. The two slot antennas face each other and form an angle having a value, for example, 20 degrees, dependent upon the phase velocity in guides 6 and l and such that maximum action occurs along the bisector of the aforesaid angle. The branch guides 6 and l and the main guide 8 are each equipped with a reflective transverse end wall ID. The inner conductor 4 of line 2 projects into the stem section 8 in a direction parallel to the a wall of section 8 so that the main guide 8 and the branch guides 6 and l transmit and receive H11 waves polarized horizontally, that is, in a direction aligned with the transverse or shorter dimension of each of slots 9. As described so far, the structure constitutes the well-known prior art V leaky pipe antenna. In accordance with the invention, triangular metallic shield members II and I2 are provided, each member being attached to corresponding b walls of the two branch guides 6 and l. The two members II and I2 form a linear aperture antenna l3 having a longitudinal axis I l perpendicular to bisector l0 and a transverse dimension or width l 5 greater than the width of either of slots 9. In other words, the members II and [2 function to transform the two narrow slot antennas 9, each angularly related to bisector I0, into a wide aperture antenna I3 perpendicularly related to bisector I0.

In operation, Fig. 1, centimetric waves generated in the transceiver I are supplied over line 2 to the guide section 8 and thence to the two legs 6 and I, the wavelets conveyed in wave guide branches 6 and 1 and delivered to the slot antennas 9 being horizontally polarized as shown by arrows I6. The wavelets emitted through the two slot antennas 9 combine in phase, by reason of the critical angle between the slots *9, for the direction I! which is aligned with the bisector of the angle formed by the slot antennas '3. Stated differently, considering the verticalplane :containing the branch guides 6 and I and hereinafter denoted th magnetic plane, maximum action occurs in the direction N. Considering the horizontal or the electric plane containing bisector Ill and perpendicular to the magnetic plane, the triangular members I I and I2 function to prevent side radiation and in general .to produce. maximum action in direction II. In the case of reception, the reciprocal operation obtains, as is well known, and echo waves reflected by a distant target are collected by the aperture antenna I3.

Referring to Fig. 2, curves I8 .and I9 illustrate, respectively, the magnetic plane and electric plane directive characteristics for the system of Fig.. 1. It will be observed that the maximum lobe 20 of the magnetic plane characteristic is relatively narrow, that is, about 7 degrees wide at the half power point corresponding to 0.7 On the power square root scale. Also, beginning at points 2| and 22 'on curve I9 corresponding, respectively, to the +25-degree and the .20. deg r'ee directions, the curve slopes downwardly at each end, so that sidewise radiant action, as for example, radiation and reception in the +50-degree or 50- degree direction, is minimized.

Fig. 3 illustrates a structure comprising a cylindrical parabolic reflector having its line focus energized by the antenna of Fig. 1. In more detail, reference numeral 23 denotes a cylindrical parabolic reflector and numeral 24 designates the line focus of reflector 23. A V leaky guide antenna equipped with triangular shields II and I2, as illustrated by Fig. 1, is Positioned so that the longitudinal axis I4 of linear aperture antenna I3 is aligned with the focal line 24. The reflector 23 and the focal line 24 have a length equal approximately to the length of the aperture antenna I3. Numerals 25 and 26 denote sectoral end shields each extending between an extremity 21 (Fig. 1) of the aperture antenna I3 and the associated extremity 28 of the reflector 23.

In operation, Fig. 3, microwaves emitted by the aperture antenna I3 energize the entire line focus 24 of reflector 23 and, in the electric plane, an exceedingly sharp directive lobe 29, Fig. 4, is secured. In the case of reception the parabolic reflector functions to receive the echo waves and to energize the aperture antenna I3 throughout its length. Considering the magnetic plane, the directive characteristic is similar to the magnetic plane directive characteristic for the system of Fig. 1. In Fig. 4, reference numerals 30 and 3| denote the measured magnetic plane directive characteristics of the structure of Fig. 3 with and without the end- pieces 25 and 26, respectively. It will be noted from these two curves that in practice the end- pieces 25 and 26 function to secure an improved magnetic plane characteristic .infismuch as the minor lobes 32 of curve 30 are smaller than the minor lobes 33 of curve SI, and the nulls 4 34 of curve 30 are deeper than the nulls 35 of curve 33.

The lobe switching antenna of Figs. 5 and 6 comprises a cylindrical parabolic reflector 23, such as used in the system of Fig. 3, and two V-shaped directive antennas 5 each equipped with triangular shield members II and I2, as illustrated by Fig. 1. Therectangular apertureantennas I3 and the focal line 24 of the parabolic reflector are parallel to each other and the focal line 24 is included between the two aperture antennas I3.

-Numera136 denotes the principal axis of the parabolic reflector. The sectoral end- pieces 25 and 25 each extend between the transverse edges 21 of :both'aperture antennas and the corresponding edge 28 of reflector 23. The transceiver I is connected by coaxial line 2 to a main wave guide section '31 and to a wave guide switch 38 of the type disclosed in my Patent 2,409,183 granted on October 15, 1946. The switch 38 comprises two detuning chambers 39, a partition 43, a rotatable vane 4I, two near-end orifices 42 facing guide section 3] and two far-end orifices 42 facing guide sections 8. One of the far-end orifices 42 connects the left chamber 39 to section 8 of the left-hand antenna 5 and the other orifice 42 connects the right chamber 39 to section 8 of the right-hand antenna 5. The vane is continuously driven by means of a motor (not shown).

In operation, Fig. 5, the pulse energy generated in transceiver I is supplied over line 2, guide section 3.1 and switch 38 alternately to the two antennas 5. Since one aperture antenna I3 is positioned on the left side, and the other on the right side, of theiocal line 24, the direction of maximum radiant action is switched between two paths making equal angles with the axis 35' of the reflector 23. Thus, referringto Fig. 6, with the left aperture I3 connected by switch 38 to the transceiver I, maximum transmitting and receiv-- ing radiant action occurs in the right or minus direction 43 and with the right aperture connected by switch 38 to transceiver I maximum transmitting and receiving action occurs in the plus direction 44, these directions making equal angles with the axis 36 of the reflector. As shown in Fig. "I, the directive characteristic 45 for the system comprising the reflector 23 and the left aperture I3 is substantially the same as the directive characteristic 46 for the system comprising the reflector 23 and the right aperture I3. Moreover, each directive characteristic is highly satisfactory since the nulls 41 are deep and since the minor lobes148 are relatively small. In connection with Fig. '7, it is important to note that the curves 45 and 46 illustrate separate and distinct charac teristics and not different positions of the same characteristic. Stated briefly, the directive characteristic does not move gradually from the position shown by curve 45 to that shown by curve 46 but is switched or jumped from one position to the other. In radar operation, with the axis 36, Figs. 6 and 7, aligned with the target, echo pulses having the same intensity are received by both antennas, the intensity being 0.8 as indicated by reference numeral 49 onthe vertical field scale, Fig. 7.

Referring to Fig. 8, which illustrates a lobe sweeping antenna'reference numeral 50 denotes a leaky wave guide of the first kind having a pair of transverse end reflective walls I0, .a longitudinal slot antenna 5| and a length of approximately o e-half avelength as measured in the guide. The guide 50 ispositioned so that the slot antenna 5| extends parallel to the focal line 24 of a cylindrical parabolic reflector 23, the focal line being included between the reflector 23 and the slot antenna 5|. The guide 50 is connected to the transceiver by a coaxial line 2 having a rotatable junction or coupling 52 such as disclosed in my copending application mentioned above. A shaft 53 is attached to the bottom of guide 5| and is connected through the coupler 54 to motor 55. With motor 55 operating, the coupler 54 functions to oscillate shaft 53 and slot antenna 5| through a predetermined angle, for example, 20 degrees, so that the slot antenna 5| moves back and forth through the focal line 24, the angle being centered on the axis 36 of reflector 23. The mean position for guide 50 is denoted by reference numeral 56.

In operation, Figs. 8 and 9, pulsed centimetric waves supplied over line 2 from transceiver l are emitted through the slot antenna 5| in a broadside direction perpendicular to the plane of the slot 5| and are then focussed by the reflector 23. Upon reflection by the distant target the wavelets collected by reflector 23 are supplied to the linear slot antenna 5| and thence conveyed to transceiver With the slot antenna 5| at the extreme right or plus position, Fig. 9, maximum radiation is in the left or minus direction 51 and the major lobe of the directive characteristic has the position denoted by numeral 58. As the slot antenna 5| rotates to the left, the direction of maximum action moves toward the right. With the slot antenna 5| in the mean position the direction of action is aligned with the reflector axis 36. When the slot antenna 5| is in the extreme left or minus position, maximum action occurs in the right or plus direction 59, the position of the major lobe of the directive characteristic being denoted by reference numeral 60. As indicated by the major lobe peaks 6|, 62 and 63, as slot antenna 5| oscillates the major lobe moves back and forth between the extreme positions 51 and 59, and radio scanning obtains.

The lobe sweeping system illustrated by Fig. 10 differs from that of Fig. 8 primarily in that the line 2 is connected to the mid-point 64 of the leaky guide and the leaky wave guide 5|] is maintained stationary. The lobe sweeping action is accomplished by means of an auxiliary metallic reflector or vane .65 having the two parallel reflector surfaces 66 and 61. As in Fig. 8, numerals H3 denote end reflective wall members. Assuming the transverse magnetic plane dimension of the leaky guide 56, Fig. 10, is the same as that of the leaky guide 5|) of Fig. 8, the length of guide 50 of Fig. 10, as measured in wavelengths in the guide, is twice that of the guide 50 of Fig. 8. The shaft 53 associated with motor 55 extends longitudinally through vane 65 and, in operation, the vane is continuously rotated. The rotatable vane 65 is included between the slot antenna 5| and the reflector 23; and the focal line 24 is aligned with the slot antenna 5|.

In operation, Fig. 10, centimetric energy is supplied to and received from the slot antenna 5| by transceiver I over line 2. During one-half revolution of vane 65 the reflective or mirror side 66 faces the slot antenna 5| and an image slot antenna exists. With the transverse axis 68 of vane 65 perpendicular to the axis 36 of the parabolic reflector 23, the image slot antenna is on the axis 36 as shown by reference numeral 69, and with the transverse axis parallel to the axis 36 the image antenna is absent, that is, the vane functions as if removed. As vane 65 moves through one-half revolution the image antenna moves from the position shown by numeral" through the focal line 24 to the position shown by numeral H; and the couplet formed by the slot antenna 5| and its image makes one complete right-to-left sweep through an angle centered on the axis 36. Consequently, the beam or lobe produced by the combination or couplet comprising the stationary primary slot antenna and the moving image antenna formed by the vane makes one complete sweep for one-half revolution of the vane 65. Similarly, during the remaining half-revolution, the reflector side 61 faces the slot antenna and the couplet makes a complete sweep. Thus, there are as many sweeps per revolution of shaft 53 as the number of reflective sides of vane 65. If vane 65 were four-sided, as in the structure illustrated by Fig. 13, four sweeps would be made during each revolution of shaft 53.

Referring to Fig. 11, curves 12 and 13 denote, respectively, the measured electric (horizontal) and magnetic (vertical) plane directive characteristics for a structure constructed in accordance with Fig. 10, substantially, except that the vane 65 is omitted. As shown by these curves, maximum action for the system without vane 65 occurs in a direction aligned with the parabolic axis 36. The magnetic plane characteristic comprises substantially only a .single lobe in view of the directive action of the slot antenna 5|; and the electric plane characteristic comprises substantially only a single lobe by reason of the directive action of reflector 23.

Fig. 12 illustrates the measured lobe-sweeping characteristic of a system constructed in accordance with Fig. 10 and including a rotating vane. Thus, the maximum lobe 14 is at the left of axis 36 when the reflective side 66, or 61, of vanes 65 is oriented so that the image antenna is at the right of axis 36 and in the position denoted by numeral 10. When the reflective side 66, or 61, is positioned so that the image antenna is at the left of axis 3'5 and in the position denoted by numeral H, the maximum lobe 15 is at the right of axis 36.

Referring to Fig. 13, the lobe sweeping antenna is fundamentally the same as that of Fig. 10, except that a corner reflector 16 of the type disclosed in Patent 2,270,314 to J. D. Kraus, issued January 20, 1942, is used instead of a parabolic reflector and a four-sided auxiliary plane reflector 11 is employed instead of a two-sided vane. The rotating quadrilateral reflector 11 extends paral lel to the corner reflector and is included between the slot 5| and the corner reflector 16. In operation, the maximum transmitting lobe for the entire system makes one complete right-to-left sweep during a quarter-revolution of reflector 11, that is, one sweep for each of the reflective sides 18.

Although the invention has been explained in connection with certain embodiments, it should be understood that it is not to be limited to the apparatus disclosed, inasmuch as other equipment may be employed in practicing the invention.

What is claimed is:

1. A lobe sweeping antenna comprising a rectangular wave guide having a longitudinal slot antenna, a transceiver connected to said guide, and means for moving said guide about a longitudinal guide axis.

2. A lobe sweeping antenna comprising a rectangular wave guide having a longitudinal slot antenna, a transceiver connected to said guide,

means .for oscillating said guide about 'a longitudinal guide axis, and a .concave areflector facing said-slot antenna.

3. In combination, a-cylindrical'parabolic antenna reflectorhavinglafocalline, a=wave guide having a longitudinal slot antenna extending parallel ,to said-focal .line and facing said refiector, a transceiverlconnected to saidguide, and means for oscillating said slot antenna.

4. In combination, a triangular wave; guide antenna :comprising :two zangularly related wave guideshaving longitudinalslotsfa'cing each other and connectedto la -transceiver,-apair of triangu- 18.1";Sid815hi61d members each extendingbetween a pair of correspondent sides ,of'saidguidea-said shield members forming a -linear aperture antenna extending perpendicular to :the bisector of the:angle.between SSJdwSlOtS.

5. In combination, a wave ;guide :antenna in accordance with :claim 4, and a cylindrical parabolic reflector having :its decal line ialigned withsaid linear aperture antenna.

16. in combination, :a wave guide antenna :in accordance 'with claim .4, :azcylindrical parabolic reflector having a alength substantially equal-to the length o'fsaid aperture antenna .and a focal line aligned with said .iinear iaperture antenna, and:-a pair of endlshield members each extending ibetween correspondent extremities of said aperture antenna ;and.rsaid :reflector.

at a given point to a translation device and -'having at "least one end reflecting '-wall, said pointand reflecting :wall being spaced :a half of :a guide wavelength, whereby) the directly propagated :and reflected energies are cophasal.

10."In acombination;alcylindrical parabolic reflector having 'alline'focus, a :wave guide having a longitudinal slot :antenna lcoincident with-said 'focus, and a translation device connected 'to sa'id :guide.

11. 'In.cornbination,la(concave'reflectorihaving l a :line focus, a 'smetallidwave :guide :having' at least .-one transverse reflecting wall, said guide having a longitudinal :slot :antenna facing -said srefiector, a translat-ion device connected athereto 8 at a-given point, the distance betweensaid point and said transverse well being electrically equal to-a half of a guide wavelength, whereby the waves as-emitted or collected-at said .point and the waves as-reflected at saidtransverse .wallare cophasal.

12. A'lobe'sweeping antenna system comprising a hollow reflector, a waveguide having a longitudinal slot antenna extending parallel 'to and facing said reflectonatransceiver connected to said guide, a linear reflective vanepositioned parallel toand includedbetween said slot antenna and said reflector, and means 'for rotating said vane.

13. A lobe sweepingrantenna system in accordance with claim 12, said reflector being a cylindrical parabolic reflector.

14. A lobe sweeping antennasystem in'accordance with-claim 12, said vane having two refleeting surfaces.

15. In'combination, a linear wave guide comprising apair'of transverse end reflective walls anda side wall extending therebetween, said side .wall containing-a slot antenna, the longitudinal dimension of said guide being equal to a half wavelength -or a multiple thereof, as measured in the guide, said wavelength being dependent upon a'transverse dimension of the guide, and a 'translation device connected to said guide, Wherebysaid longitudinal dimension is dependent upon said transverse dimension and the phase velocity-oi said guide. and maximum transmitting orreceiving actionoccurs in a'directionrperpenicular to said side wall.

16. In combination, a cylindricalzparabolicreflector having a focal line, a linear rectangular wave guide comprising a side wall containing a slot antenna, apairof transverse end reflective wall connected to the extremities of said side wall and spaced-a distance equal to a wavelength as measured in the guide, and a translation device connected to the mid-pointof said guide.

ALFRED 'C. 'BECK.

Name Date Southworth July 9. 1940 Clavier Oct. 24, 1933 Ilberg May 21, 1935 Hansen June 25, 1946 FOREIGN PATENTS Country Date Great Britain Oct. 15, 1931 Number Number

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