US2663797A - Directive antenna - Google Patents

Description

Patented Dec. 22, 1953 Laboratories, Incorporated;

c po a n of New X012 ApplicationMayfi; 1949, Serial No. 91,572

- Claims. (Cl. 250= 33.6 3)

This invention relates. to antennas. for trans:

mitting and receiving electromagnetic. waves-sand. particularlyto linear end-n antennassuitabl'e, for use in directive, and non-directive.iradioran-q tenna systems.

As is known, and as is disclosed inPatent 2,425,336, granted on August 112,. 1947,.to.-G.E. Mueller, linear end-on directive rod antennas formed ofsolid dielectric material, such asxpolye styrene, have been suggested foruse in themicro-H wave field. As ordinarily used, the dielectric rod antenna, or so-called polyrod, of the. Mueller, patent is connected to a. transmission system of the wave-guide. type. While. inlgeneralthe. polyrod is highly directiveand-otherwise adequate from an electrical standpoint, it islnotentirely satisfactory from. a mechanicalstandpoint,

especially in certain installations because-of the fragile nature of the solid dielectric material.

Moreover, while the polyrodmay-be associated.-

with a transmission. system of the coaxial linetype, as. disclosed in theMueller patent, it-is not readily adapted for use with a two-.wire linesuch as is employed, for examplainultra-shortwave television receiving systems-N Accordingly, it now appears desirable to obtain a linear end-on -antenna which is devoid ofthedistadvantages-in herent in the dielectric-rod antenna and which also possesses distinct attributes not found in the prior. art end-on linearantennas.

It is one object. of this; invention to obtairr-a highly directive linear v end-one antenna.-of:--rig-id-:

construction.

It is another objector-this invention. to ;obtain a highly directive end-on antenna array suitable;

for matchingto a two-way ultra-high freguency transmission line.

It. is' still another object of thisinvention to obtain a simple inexpensive broadcast or o nni directional antenna having alow. angle of fire In accordance with one embodiment, of theinvention a linear endon antenna, comprisesa row or linear assembly of small circular metallic disks.

attached to and spaced along a fmetallic rod. The rod is aligned with the axis of a conical horn.

and is attached by braces to diametrically 'op -a posite points of the mouthperiphery, andcppoef, site points of the throat periphery. A circular,

guide connects the throatof the hcrntoa trans:

lation device. The metallic structure comprising.

the spaced metallic disks constitute s anartificial dielectric medium f or electromagnetic wayes and,

in operation, radio waves propagated, along-the,

axis of the hornand structure a inthe polyrod, so that end on dir is obtained. 9

delayed, as; tire m en.

The linear assemblyor rowcf metallic disks, disclosed and claimed herein asnan 'electromag-l netic antenna, is also disclosed-J"and claimed. in (1) my companion. concurrent-1y. filed applica-v tion Serial No. 915,571 as an' acoustic device, and

in (2) my concurrently filed-companion application: Serial. No. 91,573 -as an electromagnetic wave guide.

The invention will be :more -fullyunderstood 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'wiew of 'a microwave systemcomprising-a sin'gl'eiendecn metallic linear antenna constructed: in accordance: withthe invention Fig. 2 is a perspective-view o'f- -a microwave sys-" tem' comprising a dual: end-orr metallic -linear antenna constructed in=accordance withthe-invention and suitable for use-with a two-wire ultra-high frequency-line; and

Figs. 3 and 4 are respectively topandsideviews of an ultra-high" frequency low-fire broadcast antenna system constructed; accordance with" the invention.

Referring to- Fig. -'1', th'ereis -'shown--amicrowave;

end-on antenna unit I-- comprising a roworassembly 2 of small circulanmetallic disks 3"attached to and spaced-uniformly alongrthe entire length of a brasslinear member or rod' t. The

rod extends through and-is 'aligned' with the axis 1 5 of a small conical horn' 'fi having -a mouth I and a throat 8; The horn throats-is connected to: a translation- -dev-ice=-9; "such" as a microwave transmitter or receiver, through a circular-guide l0; The rod 4 1s fastened-by -means -oftwo linear metallic blfiC8SOI StI-lltSj' I l to diametricallyopposite 7 points of the circular periphery of the.

horn mouth and,-- 'similarly,- itr'is attached byv struts l I to opposite points on, the?" circular periphery of the hornthroat: The'ystruts-l I atzthe' horn mouth 1, and at-the horn throat-8; extend perpendicular to the electric-polarization- I 2 of the waves transmitted or-received: Hence the 1 end-onantennaie suitable for use with a single polarization. The-struts!l-"mayyhowever, be?

formed of dielectric materialin which case any polarization perpendicular-Ate the axis 5' may beemployed. Alsoifonly oneapolarization isused; instead, of the disks 3-,; lineammetallic; elements i having; a length equal: totheaadia'meters of. the

disks and extendm rparallel to the-polarization maybe used" 7 he d meterD. or eachvdiskv-l nd has acina- S between adjacent disks are each preferably not greater than a quarter or the design or mean wavelength in the operating band. In short, the conductive disks and the spacings are each very small compared to the wavelength, so that for a given band of wavelengths a constant delay factor is secured. Also the disks external to the horn have equal diameters, whereas the diameters of the disks inside the horn are preferably graded in accordance with the horn flare for the purpose of effecting a satisfactory coupling or match between the horn 6 and the metallic assembly 2 of disks. By way of example; in one tested embodiment, designed for a mean wavelength of ).=3.2 centimeters corresponding to 1.26 inches, the length and the diameter of the rod 4 were respectively about 12.0 and 0.03 inches.

About forty disks 3 were installed on the rod;)

and the thickness T, diameter D and spacing S of the disks were respectively 0.06, 0.25 and 0.375 inch. If desired, the diameters of the disks external to the horn may differ, and the spacings between disks may difier. Also, the linear rod 4, which functions merely as a support for the disks 2 may be formed of a non-fragile dielectric, instead of conductive, material. As explained below, the metallic disk structure 2 constitutes an artificial dielectric medium of the type disclosed in my copending application, Serial No. 748,447, filed May 16, 1947, Patent No. 2,579,324, issued December 18, 1951, and, in operation, functions to delay the velocity of the electromagnetic (transverse) waves propagated along a path coincident with the common axis 5 of the assembly or row 2 of the horn 6.

Considering the transmission operation in more detail, microwaves having a polarization I2 are supplied by device 9 over guide It! to the horn 6 and a wave having a spherical front is established at the horn mouth. The wavelets Or rays propagated along the axis of the metallic row of disks are delayed, as stated above, so that the spherical front is to a large degree converted to a plane front, as in a lens, and a high degree of directivity is obtained. In reception, the converse operation is secured. Thus the end-on metallic antenna unit I or, more accurately, the metallic assembly or structure 2, is comparable in operation to the solid dielectric rod disclosed in the above-mentioned Mueller patent. Also, it may be noted that the end-on metallic structure 2 is similar to the so-called Yagi director array disclosed in Patent No. 1,745,342 in that both systems produce a unidirective effect. The end-on antenna unit 1 and the Yagi array differ materially, however, both in structure and in function.

Referring to Fig. 2, the two-wire end-on microwave antenna system comprises two end-on antenna units I each similar to the unit I of Fig. 1. Each unit I is supported by a linear conductive member 2i, the two ends of each unit 1 being attached to the associated supporting member 2! through the insulators 22. The two linear conductors 2| constitute a two-wire line and are conductively connected to the inner surfaces of its opposite sides 23 of a rectangular guide 24. The guide 24 is connected to the translation device 9. As shown on the drawing the linear conductors diverge from the guide 24, that is, to form an acute angle 0. of say 5 degrees. The plane of the linear conductors 21 is parallel to the electric polarization l2 of the waves utilized.

In operation, Fig. 2, waves are supplied from the device 9 over guide 24 to ,thetwo conductors 2| and energy is induced in the two. antenna units 4 I. Each unit I radiates end-on, as in Fig. l, and maximum radio action occurs along a direction 25 coincident with the bisector 26 of the angle a. The directive action along the direction 25 is enhanced by reason of the angular relation of the conductors 2!. As in Fig. 1, in reception, the converse directive action is obtained. As already indicated, if desired, the two linear conductors may be connected, and matched, to a conventional two-wire line, such as a television receiving line, instead of to the guide 24.

Referring to Figs. 3 and 4, the omnidirectional antenna system 30 comprises in eifect several end-on linear metallic assemblies extending radially abouta conventional omnidirectional turnstile primary antenna. More particularly, the antenna system 30 includes a conventional turnstile antenna 3i comprising the crossed dipoles 32 and 33 which are connected by the coaxial lines 34 to the translation device 9. A quadrature phase shifter 35 is included in one of the lines 34. Numeral 36 denotes a metallic delay structure comprising short metallic linear elements 31 mounted in a dielectric retaining member 38 and arranged along the circumferences of concentric circles. Preferably, each element 31 is not greater than a quarter wavelength long. As shown on Fig. 3, certain elements 31 are parallel to dipole 32 and other elements are parallel to dipole 33. As explained below, however, the turnstile radiates in all directions in the horizontal plane so that the elements 3! may be disposed or oriented in a manner different from that illustrated in Fig. 3. The size and spacing of the electrically conducting linear elements 31 are such that the metallic structure 36 formed by the elements constitutes an artificial dielectric, as disclosed in my copending application Serial No. 748,447, and functions to delay waves propagated along each horizontal path extending outwardly and radially from the turnstile antenna 31 at the center of the metallic structure.

In operation, Figs. 3 and 4, waves supplied by the ultra-high frequency device 9 over coaxial lines 34 to the crossed dipoles 32 and 33 are radiated omnidirectionally in the horizontal plane in a manner well understood in the art. The radiated waves are horizontally polarized and, considering the vertical plane action, the flat circular metallic medium 36 delays the waves propagated horizontally so that a sharp beam extending horizontal is obtained. In other words, the metallic structure produces a low angle of fire and minimizes undesired radiation toward the sky.

While the invention has been explained in connection with certain specific embodiments it is not to be limited to the embodiments described inasmuch as other apparatus may be employed in successfully practicing the invention.

What is claimed is:

1. In combination with a source of horizontally polarized electromagnetic waves having a preassigned wavelength and a wave guide of circular cross section for transmitting said waves coupled to said source, means coupled to said wave guide for launching into free space waves generated by said source and transmitted by said guide which comprises an outwardly flaring metal horn disposed coaxially with said guide and having a circular throat section of diameter equal to that of said guide, and a circular mouth section of substantially greater diameter, the throat section being conductively connected to said guide throughout its circumference, a first diametral metal strut extending vertically across said throat section and connected thereto at each of its ends, a second diametral metal strut extending vertically across said mouth section and connected thereto at each of its ends, a metal rod connected to the midpoints of said struts and supported thereby extending coaxially with said horn and said guide throughout the length of said horn and outwardly thereof for a distance at least several times said preassigned wavelength, said rod thus comprising two portions, one of which is exterior to said horn and the other of which is interior to said horn, a first plurality of free-edged metal discs mounted on the exterior portion of said rod and coaxially therewith in planes normal to the axis of said rod and connected to said rod at points which are uniformly spaced apart by more than one-quarter wave length and less than one-half wavelength of said waves, each of said discs having a diameter slightly less than one-quarter wavelength and a thickness of substantially onetwentieth wavelength, the periphery and each face of each disc being exposed to free space, a second plurality of free-edged metal discs mounted on the interior portion of said rod and coaxially therewith in planes normal to the axis of said rod and connected to said rod at points which are uniformly spaced apart by more than onequarter wavelength and less than one-half wavelength of said waves, each of said discs having a thickness substantially one twentieth wavelength, the periphery and each face of each disc being exposed, the diameters of the discs of said References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 706,739 Fessenden Aug. 12, 1902 2,178,299 Dallenbach 'Oct. 31, 1939 2,283,935 King May 26, 1942 2,323,641 Bailey July 6, 1943 2,351,723 Vogel June 20, 1944 2,455,888 Brown Dec. 7, 1948 2,485,920 Riblet Oct. 25, 1949 2,492,358 Clark Dec. 27, 1949 2,577,510 Cohn Dec. 4, 1951 2,588,610 Boothroyd et a1. Mar. 11, 1952 OTHER REFERENCES Wave Guides by L. G. H. Huxley (MacMillan 1947), pages 198 to 203.

Bell System Technical Journal, vol. 27, pages 58 to 82, January 1948.

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