US2462881A - Antenna - Google Patents

Description

March 1, 1949. J. w. MARCHETTI ANTENNA 2 Sheets-Sheet 1 Filed Oct. 25, 1943 INVENTOR. JOHN W. MARCHETTI.

TRANSDUCER KEYER 2 HORIZONTAL D IS'T'A NCE March 1, 1949. 2 J. w. MARCHETTI 2,462,881

ANTENNA Filed Oct. 25, 1943 I 2 Sheets-Sheet 2 JNVENTOR. JOHN w MARCHETTI TO MOTOR :trackingi Patented Mar. 1, 1949 16 Claims.

The invention described herein may be manufactured and used by or .for the Government ,for governmental purposes, without the payment to me of any royalty thereon.

The present invention :relates to antenna systems, and more particularly :to directive antenna systems of the type wherein the -directivity of the systemic adapted to be periodically and cyclically shifted independently of any movement of the antenna.

In radio pulse-echo object-locating systems, it is desirable :to :be :able :to so control the directivity of the transmitting and/or the receiving antenna that the directivity can, at will, be warped in any desired direction :and by any-given amount from the normal unwarped direction of the antenna. It is also desirable to be able :to wobble, selectively and at .a predetermined frequency, :the antenna directivity about the said normal unwarped direction, in order 130580311 :any desired sector of the space surroundingrthe system without .moving the antennaitself.

Apparatus for and methods of so controlling the antenna idirectivity, together with a description of the complete system in which the said apparatus .and methods may be embodied, are disclosed Jill the following co pendin'g patent applications: James R. .Moore, Serial Number 467,266,;file'd November 28, I942; JohnJ. Slattery, Serial Number 506,520, .filed October 16, .1943; and Delbert A. Deisinger, :Serial Number 5'06,522, filed October 16, 1943; all assigned to the same assigneeas my present application.

Asset forth, in detail, in the above identified Joe-pending applications, directivity wobbling, or

"flobe switching, as the operation is commonly called, :is particularly well suited for tracking aerial and/ or surface targets "by radio pulse-echo means according *to the method known as"double interaction sof direct and earth aeflected icom- However, T have discovered another (Granted under the act of March 3, .1883, .as amended April 3.0, 1928; 370 0. G. 757) .ponents -.of the radiation, which .at certain points results ,in reinforcement .and at other points in cancellation, theregionsurrounding the antenna system is characterized by the presence of .zones in wh h a hi h d gree of sensitivity is obtainable and other zones in which a relatively lower degree .of sensitivity is available. The latter are sometimes referred to as nullzones, zones of silence or gaps. .In this specification .all three expressions will be .usedsynonymously andinterchangeably. Obviously, the presence of .such :zones is extremely undesirable in systems .of the type described in the .-above-..named applications, inasmuch as they are regions wherein craft .may lurk relatively free from detection by radiolocat- ,ing systems. It is, therefore, to the problem of the .elimination or the minimizing of said gaps that my invention is particularly addressed.

Thus, it is .a principal objectiof my invention .to provide a ylobe switching antenna system whereby null zones .or the like, maybe eliminated or at least reduced toa minimum.

It has been found that gap-filling radiation .can be obtained by means .of an antenna system comprising a plurality of directive antennas disposed in spaced vertical alignment and connected-by means oLa branch feed line, toa com- :mon transducer which may be either a transmitting or a receiving radio apparatus. The feed line branches are of equal electrical length .so that, under normal circumstances, the energies fed to the separate antennas are .in mutual phase coincidence.

The space pattern of such .a system .discloses several divergent directions in which the radiation is transmitted with maximumefliciency or, in the case of a receiving antenna, from which radiation is collected with maximum ,efliciency. These SO'rCfiHQddiIGCfiDl'lS-Of maximum sensitivity :arcseparated -fromzeach other by the null zones 'OITZOIIES of silence, .hereinbefore described. Now, .if means ,are employedto alter lthephase relation between the energies in the separated antennas by an .amount equal 'to 180, it is observed that the space pattern is .shifted in a manner such that the regions formerly correspondingtosensitivity tmaxima now become null .zones and vice versa. Hence if the phase shifting means are employed :in rapid alternation :so as to introduce the required phase shift and then remove the same, the over-all efiectisto produce-a resultant fspace pattern which is iefiectively free from said null zones.

r'If the antenna feed'lines-employedare of the coaxial type, conventional means provided =for introducing the desired phase shift involves the use of additional circuit elements in order to alternately introduce and remove, from certain of said feed line branches, a path length difference equal to a half wave length or any odd multiple thereof. The additional circuit elements often prove to be cumbersome and unwieldly, causing the structure to which it is applied to become extremely complicated.

It is, therefore, another object of my invention to provide means associated with coaxial feed lines for alternately and at predetermined frequency introducing a phase shift equal to 180 between certain ones of a plurality of antennas connected to said feed lines.

A common problem encountered in coupling an unbalanced feed line, as for example, a coaxial line, to a balanced system such as a dipole antenna, is the elimination or the minimizing of energy reflections from the point of transition between said unbalanced and balanced systems resulting in the production of R. F. currents along the outer conductor of the coaxial. Means suggested for the elimination of such reflections are of either two types, namely, a so-called quarter wave skirt or bazooka attached to the outer conductor at a point a quarter wave away from the transition point, or, a pair of longitudinal slots provided at the antenna end of the outer conductor of the coaxial line, said slots being diametrically opposite each other and spaced in quadrature with respect to the dipole attached to the feed line. For the purpose of the present invention, the latter of these alternative means is employed.

The slots divide that portion of the outer conductor in which they are formed into a pair of semi-cylindrical segments of length equal to the length of the slots. The dipole which is to be fed by the coaxial line is attached to the segments, one half of the dipole being connected to the mid-point of the antenna end of one segment and the other half of the dipole being connected to the mid-point of the antenna end of the other segment.

In accordance with the present invention the required 180 phase shift is alternately introduced between the components of an antenna system by connecting one branch of the feed line to its dipole in fixed phase relation. The other branch is provided with a variable phase shifter comprising a rotatable blade pivotally connected to the inner conductor of the coaxial and adapted to be reactively coupled to said semi-cylindrical segments in alternation.

To the accomplishment of the foregoing general objects, and such other more specific objects as hereinafter appear, my invention consists in the apparatus elements and their relation to one another as are hereinafter described and sought to be claimed in the following specification. The specification is accompanied by a drawing in which:

Figure 1 is a schematic diagram of a receiving and/or transmitting system in which my present inventionis embodied;

Figure 2 is a graph of the space pattern of a directive antenna system;

Figure 3 is a fragmentary front elevational View of the antenna system of Figure 1 drawn to a somewhat enlarged scale;

Figure 4 is an isometric view of one form of a fixed phase dipole and feed line;

Figure 5 is a similar view of a modification thereof; and,

Figure 6 illustrates a variable phase dipole and feed line.

Referring to the drawings, and in particular, Figure 1 thereof, there is shown a radio transmitter and/ or receiving unit in which my present invention is embodied. As shown, a pair of halfwave dipole antennas l0, [2 are connected by means of a coaxial transmission line to a common transducer H6. The transducer may be either a transmitter or a receiver or it may be a combination of transmitter and receiver provided with a conventional switching mechanism for alternately connecting antennas I0, l2 first to the transmitter and then to the receiver.

The transmission line I4 is branched at a junction to form a pair of symmetrical feed lines I8, which are preferably of equal electrical length and to the free ends of which are connected the said dipoles Hi and I2, respectively, in a manner which will hereinafter be described in detail. The transducer I6 when it is employed as a transmitter of high frequency radio energy, may be keyed into operation by means of a keyer 22 at a predetermined recurrence frequency. The dipoles lib, i2 are positioned at the foci of parabolic reflectors 24, 26 respectively, in order to produce well-defined, highly directional space patterns shown in Figure 2 by the full line graphs 28, 30 in the manner known to those skilled in the art.

As pointed out in the foregoing discussion of space pattern of directive antennas, regions, here generally represented by the numeral 32, lying outside of the space enclosed by the graphs 28, 30 are relatively free from electromagnetic radiation and are the zones referred to as null zones, zones of silence, or gaps.

Means for alternately varying the phase relation of the currents in the dipoles l0, [2 are illustrated in Figure 3. For the purpose of the following description the dipole I0 is assumed to be fed in fixed phase relationwhile the dipole I2 is fed in variable phase relation with respect to the dipole l0. As shown, inner conductor 34 of the feed line H! is short-circuited to outer conductor 35 of said feed line by means of a sectorial plate 36 which is fixedly connected, at its apex, to the output end of the inner conductor 34 and, at its periphery to the outer conductor 35.

The outer conductor 35 is provided with two longitudinally extending slots 38 each of which are of length equal to one-quarter wave length and which are disposed at the dipole end of the conductor in diametrically opposite relation. The slots 38, as more clearly disclosed in Figures 4 and 5, divide the outer conductor 35 into two semi-cylindrical segments 40, 42, of length equal to that of the slots 38. The dipole I0 is connected to the outer conductor 35, one half of the dipole being connected to the mid-point of the output end of the segment and the other half of the dipole to a corresponding point of segment 42.

A modified and somewhat simpler form of fixed phase connection between the inner conductor 34, the segment 40, and the dipole I0 is illustrated in Figure 5. As shown, the half of dipole I0 directly connected to the segment 40 is formed integrally with the inner conductor 34, it being merely an extension thereof bent'at right angles thereto and permanently connected, as at 39, to the segment 40 by soldering, spot-welding, or the like.

In Figure 6 the feed line 20 is similarly provided with two longitudinally extending slots 44 which divide the outer conductor thereof into two semicylindrical segments 46, 48. The dipole I2 is connected to the feedline 20, one half of the dipole being connected to the mid-point of the output end of segment '46 and the other half of the dipole being similarly connected to the mid-point of the segment 48.

Coupling between inner conductor 50 of feed line 20 to the semi-cylindrical segments #6, '48 is capacitative and may be affected by means of an arcuately shaped rotatable blade 52 which is of length equal to the length of the slots 44. To provide for its rotation, the blade is pivoted on the said inner conductor 50 by means of a cross arm 54 which supports the blade in spaced relation from the segments w, 42. In the illustrated embodiment, the cross arm 54 is connected to a spindle 5B which, in turn, is journall'ed in the inner conductor '50 and driven by a motor 58 (Figure 1). It is thus seen that couplingbetween the inner conductor 58 and the dipole I2 is alternately effected through the semi-cylindrical segments 46, 48 depending upon whether the blade 52 is presented to the former segment or to the latter during the course of its rotational movement.

When the blade 52 is presented to the segment 4'6 of the feed line 2 6, as illustrated in Figure 3 in full lines, and since plate 36 is connected to segment 40 of feed line IS, the currents fed to the dipoles ii) and I2 are in phase coincidence. However, when the blade 52 is presented to the segment 48, as indicated by the dotted lines 58, inasmuch as plate '35 continues to be connected to segment 48, the currents fed to the dipoles Ill and 12 are in phase opposition.

Referring then to Figure 2 Where, as pointed out above, the graphs 28, 36 represent the space pattern obtained when the currents in dipoles are in phase coincidence, graphs represented by the dotted lines 69, 62 represent the space pattern obtained when the dipoles ill, l2 are in phase opposition. It is clear that the space represented by the graphs 69, '62 overlap and complement the space pattern represented by the graphs 28, 30. Thus, continued rotationoi the blade 52 produces a corresponding shifting of the phase relation between the dipoles lll and I2 which, in turn, results in the production of a substantially gap free radiation pattern for the antenna. Normally, the speed of rotation of the blade is made/ equal to or an integral number of times greater than the keying frequency at which the radio transmitter I6 is pulsed, in order to assure a more complete and persistent coverage of the space sector of interest.

There has been described what is at present considered a preferred embodiment of my invention. It will, however, be understood that various changes and modifications thereof will be apparent to those skilled in the art and, it is, therefore, intended in the following claims, to cover all such modifications as fall within the true spirit of this invention.

What is claimed is: v

l. A directional antenna system comprising a pair of radiators arranged in spaced vertical alignment, a transducer, branched symmetrical coaxial feed lines connecting said radiators to said transducer, said feed lines having inner and outer conductors, each of said outer conductors being provided at the antenna terminals thereof with means for coupling said feed lines to said radiators, and means cooperating with said coupling means for varying the phase of the current in one of said radiators relative to that in the other, said coupling means comprising a pair of diametrically opposed longitudinal slots formed in said outer conductor and a transverse member connecting said inner and outer conductors.

2. A directional antenna system comprising a pair of radiators arranged in spaced vertical alignment, a transducer, branched symmetrical coaxial feed lines connecting said radiators to said transducer, said feed lines having inner and outer conductors, each of said outer conductors being provided at the radiator terminal thereof with two longitudinal slots spaced in quadrature with respect to the radiator connected to said feed line, said slots dividing-said outer conductors respectively into a pair of semi-cylindrical segments of length equal to the length of the slot, and means cooperating with said segments for varying the phase of the current in one of said radiators relative to that in the other.

3. A directional antenna system comprising a pair of radiators arranged in spaced vertical alignment, a transducer, branched symmetrical coaxial feed lines connecting said radiators to said transducer, said feed lines having inner and outer conductors, each of said outer conductors being provided at the radiator terminal thereof with two longitudinal slots spaced in quadrature with respect to the radiator connected to said feed line, said slots dividing said outer conductors respectively into a pair of semi-cylindrical segments of length equal to the length of the slot, means on one of said feed lines cooperating with one of the segments thereof for directly coupling said feed line to the radiator associated therewith, and means on the other of said feed lines cooperating with the said semi-cylindrical segments for reactively coupling said other feed line to the radiator associated therewith.

4. A directional antenna system comprising a pair of radiators arranged in spaced vertical alignment, a transducer, branched symmetrical coaxial feed lines connecting said radiators to said transducer, said feed line having inner and outer conductors, each of said outer conductors being provided at the radiator terminal thereof with two longitudinal slots spaced in quadrature with respect to the radiator connected to said feed line, said slots dividing said outer conductor respectively into a pair of semi-cylindrical segments of length equal to the length of the slot, a conducting element attached to one of said feed lines at one of the segments thereof for directly coupling said feed line to the radiator associated therewith in fixed phase relation, and means on the other of said lines cooperating with the said semi-cylindrical segments for reactively coupling said other feed line to the radiator associated therewith.

5. A directional antenna system comprising a pair of radiators arranged in spaced vertical alignment, a transducer, branched symmetrical coaxial feed lines connecting said radiators to said transducer, said feed line having inner and outer conductors, each of said outer conductors being provided at the radiator terminal thereof with two longitudinal slots spaced in quadrature with respect to the radiator connected to said feed line, said slot dividing said outer conductor respectively into a pair of semi-cylindrical segments of length equal to the length of the slot, means on one of said feed lines cooperating with one of the segments thereof for directly coupling said feed line to the radiator associated therewith in fixed relation, and a blade pivotally connected to the other of said lines cooperating with the said semi-cylindrical segments for reactively coupling said other feed line to the radiator as sociated therewith.

6. A directional antenna system comprising a pair of radiators arranged in spaced vertical alignment, a transducer, branched symmetrical coaxial feed lines connecting said radiators to said transducer, said feed line having inner and outer conductors, each of. said outer conductors being provided at the radiator terminal thereof with two longitudinal slots spaced in quadrature with respect to the radiator connected to said feed line, said slot; dividing said outer conductor respectively into a pair of semi-cylindrical segments of length equal to the length of the slot,

a conducting element connected across said inner and outer conductors of one of said feed lines for directly coupling said feed line to the radiator associated therewith in fixed phase relation and a blade pivotally connected to the other of said lines cooperating with the said semi-cylindrical segments in alteration ior reactively coupling said other feed line to the radiator associated therewith whereby the phase of the current in said last-named radiator is periodically varied relative to that in said first-named radiator.

7. The device according to claim 2 wherein said slots are an odd multiple of a quarter wave length.

8. A directive antenna system comprising a pair of aligned two-element antennas, means to excite a first one of said antennas in a fixed phase, means to excite the second one of said antennas alternately in phase and out of phase with respect to said first antenna, said means comprising a coaxial transmission line having a pair of diametrically opposed longitudinal slots formed therein at the radiator terminal thereof, said slots being in space quadrature relative to the elements of said second antenna, a transverse member connecting the radiator terminals 013* 1 said inner and outer conductors, and means whereby said transverse member may be rotated.

9. The device according to claim 8 wherein said slots are a quarter wave length deep.

10. An antenna assembly comprising a coaxial transmission line including an inner conductor and an outer conductor, a pair of outwardly extending, diametrically opposed antenna elements connected to a terminal end of the outer conductor of said coaxial transmission line, a pair of diametrically opposed longitudinal slots formed in said outer conductor at the antenna end thereof, said slots being in space quadrature relative to said antenna elements, said slots form ing a pair of antenna element bearing segments, and'means to connect said inner conductor to one of said segments at the antenna end thereof.

11. The device according to claim 10 which further includes rneans to connect successively each of said segments to said inner conductor.

12. The device according to claim 10 wherein said slots extend from said terminal end-a-distance equal to a quarter wave length.

13. An antenna assembly comprising a coaxial transmission line which includes an inner conductor and an outer conductor, a plurality of coplanar, outwardly extending, equiangularly spaced antenna elements connected to a terminal end of said outer conductor, a plurality of longitudinal slots formed in said outer conductor at the antenna end thereof, said slots being equiangularly disposed mid-way between adjacent antenna elements, said slots forming a plurality of semi-cylindrical antenna segments, and means to connect successively the terminal end of each of said segments to said inner conductor.

14. The device according to claim 13 wherein said slots extend from said terminal end a distance equal to an odd number of quarter wave lengths.

15. An antenna assembly comprising a coaxial transmission line including an inner conductor and an outer conductor, a pair of coplanar, outwardly extending, diametrically opposed antenna elements connected to a terminal end of saidouter conductor, a pair of diametrically opposed longitudinal slots formed in said outer conductor at said terminal end thereof, said slots being in space quadrature relative to said antenna elements, said slot forming a pair of semicylindrical segments, and means to connect said inner conductor to one of said segments or to said segments in succession.

16. An antenna array comprising two vertically aligned antenna assemblies as defined in claim 15,- wherein the inner conductor of the first of said antenna assemblies is fixedly connected to one of the segments of the corresponding outer conductor and the inner conductor of the secend of said antenna assemblies is alternately connected to each of the segments of the corre sponding outer conductor.

JOHN W. MARCHETTI.

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

UNITED STATES PATENTS Number Name Date 2,213,859 Hahnemann Sept. 3, 1940 2,242,910 Hahnemann May 20, 1941 2,248,752 Goldmann et a1. July 8, 1941 2,257,815 Rocard Oct. 7, 1941 2,297,228 Kramar Sept. 29, 1942 2,307,184 Alford Jan. 5, 1943

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