US2938209A - Antenna curtain array with coupling network - Google Patents

Description

May 24, 1960 H. BRUECKMANN 2,933,209

ANTENNA CURTAIN ARRAY WITH COUPLING NETWORK v Filed Dec. 10, 1956 s Sheets-Sheet 1 GROUND 1E LEVEi I INVENTOR, HELMUT BRUECKMANN.

ATTORNEY May 24, 1960 Filed Dec. 10, 1956 H. BRUECKMANN 2,938,209

ANTENNA CURTAIN ARRAY WITH COUPLING NETWORK 5 Sheets-Sheet 2 F /6. 2 FRONT cuRTAIN LEFT WING OF 52' RIGHT WING 0F BAY PAIR BAY PAIR BAY PAIR gg BAY PAIR BAY PAIR BAY PAIR #3 #2 #l j 2 #l #2 #3 UPPER 1 E'G uPPER TIER TIER K I. LOWER LOWER TIER I TIER K I K Q Z Q l [4)' l -,5; J\TRANSFORMER 30 I8 2 TRANSFORMER 32 4 TRANSFORMER 34 ul E .J

X 0 I; I Z 2 24 7 TRANSFOjMER 40 ii/TRANSFORMER 38 ILMTRANSFORMER 36 #3 #2 #I #l #2 #3 BAY PAIR BAY PAIR BAY PAIR BAY PAIR BAY PAIR BAY PAIR LEFT WING RIGHT WING REAR CURTAIN INVENTOR,

l-IEL MU 7' BRUEC/(MANM May 24, 1960 H. BRUECKMANN 2,938,209

ANTENNA CURTAIN ARRAY WITH COUPLING NETWORK Filed Dec 10, 1956 5 Sheets-Sheet 3 FIG. 3

FRONT QURTAIN LEFT wms RIGHT wme FRONT CURTAIN 'PHASING STUB TO RECEIVER 7O REAR CURTAIN PHASING STUB LEFT WING RIGHT WING REAR cum:

INVEN TOR, HEL MUT BRUECKMA NM May 24, 1960 H. BRUECKMANN 2,938,209

ANTENNA CURTAIN ARRAY WITH COUPLING NETWORK Filed Dec. 10, 1956 5 Sheets-Sheet 4 REAR FRONT CURTAIN CURTAIN TRANSMISSION LINE SPACE RADIATION PATTERNS UNIFORM NON-UNIFORM CURRENT DISTRIBUTION CURRENT DISTRIBUTION I IN VEN TOR,

HE L MU T BRUECKMA N/V.

ATTORNEY ANTENNA CURTAIN ARRAY WITH COUPLING NETWORK Helmut Brueckmann, Little Silver, N.J., assignor to the United States of America as represented by the Secretary of the Army Filed Dec. 10, 1956, Ser. No. 627,521

8 Claims. (Cl. 343-813) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment of any royalty thereon.

This invention relates to radio antennas and more particularly to receiving antennas applicable to fixed-pointto-point radio communication in the high-frequency range, roughly defined as the range from 3 to 30 mcs.

in conventional broadside antenna arrays heretofore utilized in fixed-point-to-point radio communication circuits, the amplitude of the currents or voltages at the feed points of the antenna elements are adjusted to provide a uniform distribution of the amplitudes in the elements relative to each other. Although such uniform distribution may provide maximum directivity, the relatively large concomitant minor lobes greatly impair circuit performance inasmuch as unwanted interfering signals are received simultaneously with the desired signal. Such deleterious effects may be reduced by optimizing the relationship between the beam width and side lobe level of the resultant radiation pattern. It can be shown mathematically that, if the side lobe level is specified, the beam width of the resultant antenna pattern may be minimized and, conversely, if the beam width is specified the side lobe level may be minimized. The non-uniform amplitude distribution required to produce such an optimum relationship is referred to as the Dolph-Tchebyschefi distribution and is defined on pages 95-96 of Antennas by John D. Kraus, published by the McGraw-Hill Book Co. (1950). Heretofore, this type of distribution has been limited to broadside antenna arrays adapted to operate at much higher frequencies.

It is, therefore, an object of the present invention to provide an improved broadside antenna array having a Dolph-Tchebyschefi current distribution and adapted to operate in the high-frequency range.

It is another object of the present invention to provide an improved broadside antenna array having an optimum relationship between beam width and side lobe level.

It is still another object of the present invention to provide an improved broadside antenna array wherein pickup interference due to the side lobes in the radiation pattern is greatly reduced.

Briefly, the present invention is directed to a broadside antenna array adapted to produce a Dolph-Tchebyschefi type amplitude distribution when operating in the highfrequency range. The array includes front and rear parallel curtains arranged in a vertical plane and a pair of feed terminals. Each curtain includes an even number of bays having full-wave dipole elements arranged in a plurality of tiers spaced apart a prescribed distance one above the other. The bays are symmetrically arranged with respect to a vertical plane through the array center perpendicular to the curtains such that corresponding bays on each side of the plane of symmetry constitute a bay pair. Included further are discrete means respectively in circuit with the dipole elements in each bay pair for producing zero-phase relationship between the currents generated in the dipole elements of the front curtain bay 2,938,209 Patented May 24, 1960 pairs and zero-phase relationship between the currents generated in the dipole elements of the rear curtain bay pairs. Also included are discrete means respectively in circuit with the dipole elements of each bay pair and the array feed terminals whereby there is produced a relative amplitude distribution of prescribed values of current in the dipole elements of each front and rear curtainbay pair, with the corresponding bay pairs in the front and rear curtains having the same relative amplitude distribution. Further included are means in circuit with the zero-phase producing means and the relative amplitude distribution producing means whereby-the curr'entsgenerated in the front curtain dipole elements lead the currents generated in the rear curtain dipole elements by a prescribed phase angle. Concerning the actual arrangement of the above mentioned means in space, it is advantageous to mount them in the plane of symmetry which is electrically neutral, thus avoiding undesired coupling between them and the antenna elements.

For a better understanding of the present invention together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings in which: 1

Fig. 1 shows one-half of the antenna array with the sup porting elements omitted for the sake of clarity, and the plane of symmetry which is indicated by the brokenlines;

Figs. 2 and 3 are schematic representations of the antenna array showing the transmission lines and transformer connections;

Fig. 4 shows the configuration of the line interconnecting the feed points of the lower and upper antenna of each bay;

Fig. 5 is a schematic representation of thequarter-wave transformers and associated coupling circuits;

Fig. 6 shows a comparison of the space radiation pattern with uniform current distribution and non-uniform current distribution; and

Fig. 7 shows the relative non-uniform current distribution in the front and rear curtain antenna bays.

Referring now to-Figs. 1-5 of the drawings, at 10 there is shown a broadside antenna arraycomprising twentyfour full-wave dipole elements each adapted to be centerfed. In Fig. 1 of the drawing only one-half of the array is shown inasmuch as both halves are identical in structure. Each half of the respective, full-wave elements include three spaced parallel wires shown at 11 and 13 which are connected in electrical parallel arrangement at one end to comprise the feed points as shown at. 15 and 17. The array is formed by arranging the full-wave dipoles into four groups of sixeach, with the dipoles in-each group being colinearly aligned and uniformly spaced from one another. As shown in Fig. 1, the four groups are arranged such that two groups of six colinear dipoles are spaced one above the other in one vertical plane and the remaining two groups are spaced one above the other in another vertical plane. The vertical planes are spaced and arranged such that the two spaced lower antenna groups are above ground level in one horizontal plane and the two spaced upper antenna groups are in a higher horizontal plane. Two horizontal dipoles arranged in a vertical plane, the upper one of which is vertcially above the lower one is defined as a bay. The dipoles in the lower horizontal plane will hereinafter be referred to as a lower-tier dipole and the dipoles in the higher horizontal plane will be referred to as an upper-tier dipole. The arrangement of the six bays in one vertical plane is defined as a curtain and, to distinguish one curtain from the other, one is designated the front curtain and the other is designated as the rear curtain. The front curtainis defined as that curtain which faces the direction of maximum radiation. In Fig. l, the upper and lower-tier dipoles of the front curtain are designated generally by the symbols AF and A'F, respectively, and the upper and lower-tier dipoles of the rear curtain are designated generally by the symbols AR and AR, respectively. The entire array is symmetrical about a vertical plane I through the array center perpendicular to the curtains. This 'vertical plane is to be considered as a plane of both physical and electrical symmetry and is hereinafter referred to as'the plane of symmetry; Thus, three bays of both the front and rear curtains are on one side of the plane of symmetry P and the remaining three bays of both the front and rear curtains are on the other side of the plane of symmetry. The front and rear curtains are supported by means of towers 21, one tower being provided for each bay in the front and rear curtains. For convenience, the two innermost bays in each curtain next to the plane of symmetry P will be referred to as Bay Pair No. 1, the two outermost bays will be referred to as Bay Pair No. 3 and the remaining two intermediate bays will be referred to as Bay Pair No. 2. To distinguish between dipoles on either side of the plane of symmetry P, one side will be referred to as the left wing and the other side will be referred to as the right wing as shown in Figs. 2 and 3.

To better describe the antenna array, it is to be assumed that the desired radiation pattern is to have a halfpower beamwidth of and a side lobelevel 30 db down from the main lobe. In the case of the six bays hereinabove described, the Dolph-Tchebyschefi distribution theory calls for Bay Pairs No. 2 and No. 3 to have respective relative amplitudes of 0.69 and 0.30, with respect to the amplitude of Bay Pair No. 1 as shown in Fig. 7. In addition, co-phasal operation of all antenna elements in each curtain is required. In the description below, the term optimum operation refers to such a distribution. A comparison of the desired radiation pattern obtained with the desired non-uniform current distribution and that of a radiation pattern resulting from uniform current distribution is shown in Fig. 6.

For optimum operation, the spacing between the front and rear curtain is made .708A of the operating frequency and the lower and upper-tier dipoles of each curtain are spaced, respectively, .746 and 1.454). above ground. The feed points of the lower and upper-tier dipoles in each bay pair are connected by two-wire balanced transmission lines 12 one wavelength long and having the general configuration shown in Fig. 4. The feed points of the lower-tier dipoles of all bay pairs are interconnected by sections of two-wire balanced transmission lines whose lengths are integral multiples of two wavelengths; All lines are arranged symmetrically with respect to the plane of symmetry so that the lengths of sections from plane P to the two feed points of each line are the same integral multiple of one wavelength. As shown in Fig. 2, line section 14 connecting the lower-tier dipoles of front curtain Bay Pair No. 1 is two wavelengths long. Similarly, the feed points of the lower-tier dipoles in front curtain Bay Pair No. 2 are interconnected by line section 16 and the feed points of the lower-tier dipoles in front curtain Bay Pair No. 3 are interconnected by line section 18. Line sections '16 and 18 are 4 and 6). long, respectively, at the operating frequency. The section of two-wire balanced lines interconnecting the feed points of the lower-tier dipoles in rear curtain Bay Pair No. 1, rear curtain Bay Pair No. 2, and rear curtain Bay Pair No. 3, are shown at 20, 22 and 24, respectively. Line 20 is the same length as line 14, line 22 is the same length as line 16 and line 24 is the same length as line 18. The transmission line sections are supported in a conventional manner at intervals of half-wavelength only (not shown). To minimize the coupling between the transmission line section line section and the radiating antenna elements, a portion of each of the lines 14-24 extends downwardly in a vertical plane from the corresponding feed points for a distance at least .5). long, 'withthe remainder of each transmission line disposed in parallel relationship in a horizontal plane. Thus, the horizontal part of all the transmission line sections isat least a half-wavelength from any radiating element and relatively close to ground. By such an arrangement, it can be seen that the transmission lines of two symmetrically located bays at the plane of symmetry are connected 'in electrical parallel arrangement (Fig.3) which results automatically in an in-phase excitation with equal amplitudes of symmetrically located bays with respect to each other.

Each of the line sections 14-18 and 20-24 are connected at; their'respectivecenter points to discrete quarter-wave open-wire line balanced transformers. The lines comprising the transformers arepositionedvertically in the plane of symmetry P to minimize the coupling therebetween and the radiating elements, and the details there of are shown in Figs. 3 and 5. Referring now to Fig. 5, the transformers associated with front curtain transmission line sections 14-18 are respectively shown at 30, 32, 34 and the transformers associated with rear curtain transmission line sections 20-24, are shown respectively at 36, 38 and 40. For the sake of clarity, only onehalf the number of wires comprising each of the transformers is shown. Thus, transformers 30, 32, 36 and 38 comprise four-wire lines and transformers 34 and 40 comprise two-wire lines. As shown in Figs. 3 and 5, transformers 30, 32, 36 and 38 each have one end terminal pair respectively connected across transmission line sections 14, 16, 20 and 22, at the center points thereof. Similarly, transformers 34 and 40 each have one end terminal pair respectively connected acrossthe center points of transmission line sections 18 and 24. The remaining free terminal pairs of front curtain transformers 30, 32 and 34 are connected inelectrical parallel circuit arrangement to form a transformer apex 50 and the re maining terminal pairs of rear curtain transformers 36,

38 and 40 are connected in electrical parallel circuit arr rangement to form a transformer apex 52. Transformer apices 50 and, 52 are equidistant from the front and rear curtain, respectively, and are interconnected by a balanced six-wire transmission line 56, approximately 0.457\ long, hereinafter referred to as the front-to-backline. For optimum operation, transformers 30 and 36 are designed to have a characteristic impedance of approximately 200 ohms; transformers 32 and 38 are designed to have a characteristic impedance of approximately 300 ohms; and transformers 34 and 40 are designed to have a characteristic impedance of approximately 680 ohms. The characteristic impedances of transformers 32, 38, 34 and 40 may. be varied within certain limits for adjustment purposes. by varying the spacing by means of adjustable spacers,'or the size of the wires, or both.

Connected across front-to-back-line 56 intermediate transformer apices50 and 52 are one pair of terminals (ungrounded) 58 and 59 of a balun transformer 60 (Fig. 3). Terminals 58 and'59 represent the balanced output or feed terminals of the entire antenna array and for optimum operation it has been found that these terminals'should be approximately 0250A from transformer apex 52. Balun transformer 60 couples the output of antenna array 10 to a receiver (not shown) in the conventional manner to provide an input antenna impedance distant from input terminals 58, 59, the impedance at these terminals'equals the terminating impedance at the unbalanced terminals, except that it is balanced. Any reactive component of the impedance into which balun 60 looks at terminals 58, 59 may be tunedtout by moving shorting bar 70 a suitable distance to one or the other side of the quarter-wave position. Balun transformer 60 also serves to bleed static charges in the antenna elements to ground. Connected in parallel circuit with front-to-back-line 56 are a pair of balanced matching or phasing stubs 72 and 74, one on each side of input terminals 58 and 59. As shown in Fig. 3, the matching or phasing stubs 72 and 74 comprise balanced two-wire open lines provided with respective shorting bars 73 and 75. The length and position of phasing stubs 72 and 74 controls the phase and amplitude relationship of the front and rear curtains. Another purpose of these stubs is to aid in transforming the terminating impedances at either end of front-to-back-line 56 (which may differ greatly) and to aifect the phase shift in the front-to-back-line in such a way that the front curtain and the back curtain are excited with equal magnitude and a prescribed phase difierence. For optimum operation matching stub 72 is preferably positioned across front-to-back-line 56 .IOSX from transformer apex 50 with shorting bar 73 positioned 0.306) from the junction of stub 72 and front-to-backline 56, and matching stub 74 is positioned across line 56 .116). from transformer apex 52 with shorting bar 75 positioned 0.3m from the junction of stub 74 and frontto-back-line 56. The above mentioned electrical length of the phasing stubs 72 and 74 of .306 and 30A, respectively, may sometimes be inconvenient for mechanical reasons if their physical length equals their electrical length which is the case with all uniform lines. It is possible, however, to reduce their physical (actual) length to a convenient value, say 25A, while maintaining their specified electrical length by composing them of three approximately equal sections such that the middle section has a lower characteristic impedance than the other two. The middle section may be constructed as a four-wire line utilizing relatively thick wire, whereas the other two sections may comprise two-wire lines utilizing relatively thin wire. The spacing of opposing wires is maintained constant throughout for convenience of construction. The length of the individual sections, their impedances, spacing, wire size, etc., is in no way critical since any variations are compensated for by properly adjusting the shorting bars 73 and 75.

At the points where the transmission line sections 14-18 and 20-24 are connected to their respective quarter-wave transformers, there are provided discrete shorted transmission line stubs in the form of balanced open-wire lines each having a free space length of approximately 0.5% and connected in parallel circuit arrangement with the discrete corresponding transmission lines. These stubs are hereinafter referred to as grounding-and-tuning-stubs, and the input to each grounding stub is at the points of connection to the corresponding transmission line. As shown in Fig. 5, grounding-and-tuning-stub 80 is connected in parallel circuit arrangement with transmission line 14 and transformer 30. Similarly, grounding-andtuning-stubs 82, 84, 86, 88 and 90 are connected in parallel circuit arrangement with transmission lines 16, 18, 20, 22 and 24, respectively. Physically, the grounding-and-tuning-stubs 80-90 are mounted in the vicinity of plane P and above ground which may comprise an expanded copper sheet mesh indicated at 100 in Fig. 5. Each tuning stub includes a balanced shorting bar S, an unbalanced shorting bar U, and a terminal shorting bar T. As shown, both the unbalanced shorting bar U and terminal shorting bar T are grounded to the copper screen 100. The spacing between balanced shorting bar S and unbalanced shorting bar U of each grounding-and-tuningstub is arranged such that a reactance of prescribed value appears at the input terminals thereof for balanced excitation and simultaneously a resistance of minimum value appears at the input terminals thereof for unbalanced excitation. For optimum operation, the balanced shorting bar S of grounding-and-tuning-stubs 80, 82, 86 and 88 are placed 163% from their respective inputs, and for grounding-and-tuning-stubs 84 and 90 the balanced shorting bars S are placed .22) from their respective inputs.

The unbalanced shorting bars U of all the grounding-andtuning-stubs -90 are placed 0338A from their respective inputs.

In operation, basic design considerations require that for a physical spacing of .708) between the front and rear curtains, the front curtain at the dipole terminals lead those of the rear curtain by 75 in phase and have the same amplitude in order to obtain cancellation of the radiation field in the rear. This condition is obtained by first adjusting the phase of Bay Pair No. 1, front curtain, for a 75 lead with respect to Bay Pair No. 1, rear curtain, and making the amplitude ratio beteen them 1 to 1'. Subsequent adjustment of all the remaining bay pairs for zero-phase with respect to Bay Pair No. 1 of their respective curtain results automatically in a phase difference of 75 between the front and rear cutains of the antenna array. Matching stubs 72 and 74 aid in maintaining the phase difference of 75 and the correct amplitude ratio. The adjustment of the characteristic impedance of the quarter-wave transformers 30-40 provides the prescribed voltage or current ratio between the pairs of bays of each curtain. The phase difference between them is zero if, and only if, the phase angle of the impedances of the bay pairs are the same. Grounding-and-tuning studs 80-90 provides for the equalization of the phase angles of the impedances. The voltage or current transformation ratio equals the ratio of the characteristic impedance of the transformer, K, over the impedance of the load |Z[, or its inverse, respectively. Thus, by proper adjustment of the Ks of the transformers, any prescribed voltage or current ratio between the pairs of bays in each curtain can be obtained. With the location of the balanced shorting bar S in each of the grounding-and-tuningstubs as indicated above, co-phasal operation of all the antenna elements in each curtain is obtained. The position of the unbalanced shorting bar'U in each of the grounding-and-tuning-stubs aids in tuning out all unwanted unbalanced voltage components which may be present.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention. For example, the number of tiers or the number of bay pairs is subject to modification according to the requirements in each embodiment. Also, the rear curtain may be replaced by a parasitic reflector without abandoning the basic ideas of this invention and the antenna may be used as a transmitting antenna as well as a receiving antenna.

What is claimed is:

1. In a broadside antenna array including front and rear parallel curtains arranged in a vertical plane and a pair of feed terminals, each curtain including an even number of bays having full-wave dipole elements arranged in a plurality of tiers spaced apart a prescribed distance one above the other, said bays being symmetrically arranged with respect to a vertical plane through the array center perpendicular to said curtains such that corresponding bays on each side of said plane constitute a bay pair; means for deriving a Dolph-Tchebyscheff amplitude distribution in each of said curtains comprising discrete balanced two-wire open transmission lines respectively interconnecting the dipole elements of each bay pair in said front and rear curtains, each of said transmission lines being symmetrically arranged about said plane of symmetry and an integral multiple of the operating Wavelength, discrete means in circuit with said transmission lines at the center points thereof for producing zero-phase relationship between the currents generated in the dipole elements of the front curtain bay pairs and zero-phase relationship between the currents generated in the dipole elements of the rear curtain bay pairs, discrete quarter-wave transformers mounted in said plane of symmetry and respectively in circuit with each of the two-wire transmission lines, each of said transformers. comprisingopen-wire lines having one terminal pair connected to its associated transmisison line, the free terminal pairs of the transformers associated with the transmission-lines in circuit with said front .curtain bay pairs being connected in parallel circuit arrangement to form a first apex and the free terminal pairs of the transformers associated with the transmission lines in circuit with said rear curtain bay pairs being connected in parallel circuit arrangement to form a second apex, a frontto-back curtain transmission line interconnecting said apices, and means in circuit with said front-to-back curtain transmission line whereby the currents generated in the dipole elements of said front curtain lead the currents generated in the dipole elements of said rear curtain by a prescribed phase angle.

2. In a broadside antenna array having front and rear curtains arranged in a vertical plane and a pair of feed terminals, and wherein each curtain includes an even number of bays having full-wave dipole elements arranged in a plurality of tiers spaced one above the other, said bays being symmetrically arranged with respect to a vertical plane through the array center perpendicular to the curtain such that corresponding bays on each side of the plane constitute a bay pair; a system for coupling said feed terminals to said dipole elements whereby there is produce a Dolph-Tchebyschetf amplitude distribution in each of said curtains, said system comprising, discrete balanced two-wire open transmission lines respectively interconnecting the dipole elements of each bay pair in said front and rear curtains, each of said transmission lines being symmetrically arranged about said plane of symmetry, discrete quarter-wave transformers mounted in said plane of symmetry and respectively in circuit with each ofthe two-wire transmission lines, each of said transformers comprising open-wire lines having one terminal pair connected to its associated transmission line, the free terminal pairs of the transformers associated with the transmission lines in circuit with said said front curtain bay pairs being connected in parallel circuit arrangement to form a first apex and the free termnal pairs of the transformers associated with the transmission lines in circuit with said rear curtain bay pairs being connected in parallel circuit arrangement to form a second apex, said transformers having prescribed values of characteristic impedance such that there is produced a relative amplitude distribution of prescribed values in the dipole elements of each bay pair in said front and rear curtains, corresponding bay pairs in said front and rear curtains having the same amplitude distribution, a front-to-rear transmission line interconnecting said apices and said feed terminals, discrete means respectively in parallelccircuit arrangement with each of said transmission lines and its associated quarter-wave transformer whereby there is produced zero-phase relationship between the currents generated in the dipole elements of the-front curtain bay pairs and zero-phaserelationship between the currents generated in the dipole elements of the rear curtain bay pairs, and means in circuit with said front-to-rear' transmission line whereby the currents generated in the dipole elements of said front curtain lead the currents generated in the dipole elements of said rear curtain by a prescribed value. r

3. In a broadside antenna array comprising front and rear parallel antenna curtains arranged in a vertical plane, each curtain including six bays having lower-tier and upper-tier full-wave antenna dipoles arranged such that the lower-tier antenna dipole and upper-tier antenna dipole of each bay are spaced apart a prescribed distance one directly over the other, said bays being symmetrically arranged with respect to a vertical plane through the array center perpendicular to said curtains; means for deriving a Dolph-Tchebyscheif current-amplitude distribution in both of said curtains with the bay pair in each curtain adjacent the plane of'symmetry having a current amplitude of unity, comprising, discrete full-wave-two-wire open lines interconnecting the feed of the operating frequency and symmetrically arranged withrespect to the plane of symmetry, discrete means respectively in circuit with each of said transmission lines for producing zero-phase relationship between the currents generated in the antenna dipoles ofsaid front curtain and'zero-phase relationship between the currents generated inithe antenna dipoles of said rear curtain; a balun transformer, discrete quarter-wave transformers in circuit respectively with each of said transmission lines andarranged in said plane of symmetry, the free ends of the respective transformers associated with said first, second and third transmission lines connected in parallel circuit arrangement to form a first apex, and the free ends of the respective transformers'associated with said fourth, fifth, and sixth transmission lines being connected in parallel circuit arrangement to form a second apex, said apices being equidistant from said curtains, a frontto-rear transmission line interconnecing said apices and in circuit arrangement with said balun transformer, and a discrete shorted two-Wire line phasing stubs in circuit with the front-to-rear transmission line and disposed on opposite sldes of said balun transformer lines.

4. In 'a directional broadside antenna array with side lobes, front'and rear parallel curtains arranged in vertical planes, each of said curtains comprising an even number of bays symmetrically arranged with respect to a vertical plane through the array center perpendicular to said curtains, corresponding bays on each side of the plane constituting a bay pair, each bay consisting of a plurality of substantially horizontal dipole elements arranged in vertically spaced tiers, and means coupled to the dipole elements in each of said curtains to provide a Dolph-Tchebysch'eif amplitude, distribution in the dipole elements, said means consisting of balanced openwire transmission lines, interconnecting the dipole elements of each bay pair in said front and rear curtains, adjustable, open-wire quarter-wave transmission line transformers connected to said transmission lines and mounted in the plane of symmetry, the quarter-wave transformers being adjustable to obtain the desired Dolph- Tchebyschefl distribution, adjustable balanced openwire tuning stubs connected in parallel with each bay pair and to the quarter-wave transformers for equalizing the phase angles of the bay impedances and for tuning out transmission line discontinuities, a balun transformer connected to the quarter-wave transformers, and adjustable open-wire phasing stubs connected to the quarterwave transformers associated with the bay pairs of the front and rear curtains to'affect a cancellation of electromagnetic fields to the rear of the antenna array.

5. An array as in claim 4 wherein the dipoles are full wave dipoles and wherein the transmission lines connecting the dipoles to the quarter-wave transmission line transformers have lengths which are multiples of one wavelength.

6. An array as in claim 4 wherein the currents generated in the dipoles in the front curtain lead the currents generated in the dipoles of the rear curtain by substantially degrees.

7. An array as in claim 4 wherein each of the tuning stubs is substantially one half wavelength in length and includes three shorting elements spaced thereacross, two .of the shorting elements being grounded and the other of the elements being balanced with respect to ground.

8. In a broadside antenna array including front and rear parallel curtains arranged in a vertical plane and a pair of feed terminals, each curtain including an even number of bays having full-wave dipole elements arranged in a plurality of tiers spaced apart a prescribed distance one above the other, said bays being symmetrically arranged with respect to a vertical plane through the array center perpendicular to said curtains such that corresponding bays on each side of said plane constitute a bay pair; means for deriving a Dolph- Tchebyscheif amplitude distribution in each of said curtains comprising discrete balanced two-wire open transmission lines respectively interconnecting the dipole elements of each bay pair in said front and rear curtains, each of said transmission lines being symmetrically arranged about said plane of symmetry and an integral multiple of the operating Wavelength, discrete means respectively in circuit with said transmission lines at the center points thereof for producing zero-phase relationship between the currents generated in the dipole elements of the front curtain bay pairs and Zero-phase relationship between the currents generated in the dipole elements of the rear curtain bay pairs, each of said zerophase producing means comprising an open two-wire 26 References Cited in the file of this patent UNITED STATES PATENTS 1,963,723 Sterba June 19, 1934 2,140,145 Sterba Dec. 13, 1938 2,238,438 Alford Apr. 15, 1941 2,249,597 Brown July 15, '1941 2,269,075 Boerner Jan. 6, 1942 2,344,884 Kirkland Mar. 21, 1944 2,410,597 Brown et a1. Nov. 5, 1946 FOREIGN PATENTS 606,124 Great Britain Aug. 6, 1948 OTHER REFERENCES Dolph: A Current Distribution for Broadside Arrays Which Optimizes-the Relationship Between Beam Width and Side Lobe Leve, Proc. IRE, 34, 6, 335 (1946); H. J. Riblet, Proc. IRE, 35, 5, 489 (1947). i

UNITED STATES PATENT OFFICE CERTIFICATE GE CU ECTION Patent No, 2,938,209 May 24, 1960 Helmut Brueckmann It is hereby certified that error appears in the-printed specification of the above "numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 8, line 7, after "front" and before the comma insert curtain Signed and sealed this 22nd day of November 1960.

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting Oflicer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF "CORRECTION Patent No? 2,938,209 May 24, 1960 Helmut Brueckmann It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 8 line 7, after "front" and before the comma insert curtain Signed and sealed this 22nd day of November 1960.

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents

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