US2433924A - Antenna - Google Patents

Description

Jan. 6, 1948. RlBLET 2,433,924 v ANTENNA I Filed Aug. 1, 1945 FIG.2

INVENTOR.

HENRY J. RIBLET ATTORNEY.

Patented Jan. 6, 1948 UNITED STATES PATENT OFFlCE ANTENNA Henry J. Riblet, Cambridge, Mass., assignor, by

mesne assignments, to the United States of America, as represented by the Secretary of War Application August 1, 1945, Serial N 0. 608,295

an antenna which has a radiation pattern substantially non-directional particularly in the horizontal plane and generally in any plane parallel to the horizontal plane.

Another object of the invention is to build an antenna possessing the radiation characteristics described above which is disk shaped, with the axis of the disk in the vertical plane when radiation is horizontally directed.

Another object of the invention is to build an antenna which makes effective use of material refractive to electromagnetic waves.

Other objects, advantages, and novel features of the invention will appear more fully in the description contained herein.

In the drawings:

Fig. 1 is a sectional view of one embodiment of the invention;

Fig. 2 is a cross-section view of the embodiment illustrated in Fig. 1;

Fig. 3 is a sectional view of a second embodiment of the invention;

Fig. 4 is a sectional view of a third embodiment of the invention; and

Fig. 5 is a top plan view of the structure illustrated in Fig. 4.

Referring now to Figs. 1 and 2, a material refractive to electromagnetic radiation, that is a substance having an index of refraction considerably greater than one, say of the order of 1.6, is formed in a shape such as that of disk [0.

A preferred substance for use in the manufacture of disk is polystyrene, because of its low dielectric losses, but any substance having the desired refractive characteristics such as styramic, hard rubber, acetate butyrate or similar substances may be used. Disk [0 may be described as having substantially the form of a volume of revolution obtained by rotating the surface enclosed by curves II and I2 and axis l3 about axis !3. The customary way of orienting the antenna of the type herein described is with axis l3 vertical, and therefore, axis l3 will be termed the vertical axis herein although it will be understood that this is not intended to limit the invention.

Curves II and I2 are preferably logarithmic and symmetrical and furthermore, preferably extend out from axis l3 several free-space wave lengths at the contemplated operating frequency.

2 In its preferred embodiment, disk 10 is thus formed symmetrically on each side of the horizontal plane (a plane perpendicular to axis l3) and has a, raised or protruding center, the sides extending outward therefrom in concave fashion. Disk ID is preferably much smaller in thickness through the center than in diameter, a ratio of about 10 to one being satisfactory. Larger ratios will provide stronger directive efiects and, con versely, smaller ratios will provide less directive effects. However, the size of disk Ill will affect dielectric losses.

Disk ID may be molded or cast around an enclosed transmission line 14 and dip-ole assembly #5, which may be a hollow pipe wave guide or a coaxial type line which enters disk In along axis 3. By the construction just described, a source of radiation is provided already possessing in part the desired directive properties. In addition, by molding or casting disk In tightly about the assembly, it is thereby well supported physically and provides a weather proof covering for the radiating elements. If the structure is subjected to unusual stress, additional external supporting members may be furnished. Dipole array l5 preferably is constructed of three arcuately I in character.

shaped dipoles symmetrically arranged about line M as described more fully in the copending application of Henry J. Riblet, Serial No. 532,793, filed April 26, 1944.

A study of the disk and dipole array of Figs. 1 and 2 discloses substantial symmetry about vertical axis I3 so that a radiation pattern of the antenna in the horizontal plane, or any plane parallel thereto, is substantially non-directional However, the radiation patternin any vertical plane, that is any plane including axis l3, shows high intensity of radiation along the horizontal axis and low intensity vertically, either up or down. Visualized in such a vertical plane, the radiation pattern would appear as two similar elongated lobes extending along the horizontal axis. This is due not only to the radiation pattern of the dipole assembly 15, but to the superimposed directive effect of disk It! which itself would have a radiation pattern of the desired type, even though a source centrally located within it were entirely non-directional in character.

Another modification of the invention is illustrated in Fig. 3. Energy is brought to the antenna array by a coaxial transmission line l6, having a central conductor l1 and an outer conductor IS. The outer conductor l8 contacts a metallic plate l9 which extends normally to axis 2t. A probe 2|, which is a continuation of inner conductor l1, passes through plate l9 without making electrical contact therewith and is terminated at a second circular plate 22 similar in size to plate l9. Disk 23 constructed of material 3 refractive to electromagnetic radiation extends outwardly from plates l9 and 22 and may be continued between the plates.

Plates I9 and 22 have the efiect of a circular parallel plate wave guide of finite extent centrally excited which produces a radiation pattern si-ma ilar to that for dipole array: except that the radiation is verticall polarized. Again, disk 23 of refractive material increases. the directive effect of radiation from the antenna and provides a highly directive radiation characteristic for they combination.

Figs. 4 and 5 illustrate another embodiment of the invention. The external conductor 24 of coaxial transmission line 25- contacts a lower metallic plate 26, extending outwardly from vertical axis 21. Probe 29 is a continuation of the inner conductor 23 of line 25, and reaches to the centerof plate 3B which extends outwardly from axis 21. In the preferred embodiment, plates 26 and 30, if continued outwardly from axis 27, would join at a small angle so that they do not extend normally from axis H. The space between plates 26 and 38 is preferably filled. with some material. refractive to electromagnetic radiation and an annular filler 3| of material absorbent to electromagnetic radiation may be inserted near the periphery of the plates. Slits 32 and, 33, are cut in plates 26- and 30 respectively, preferably arcuate in shape and substantially concentric with, or coaxial with, axis 21. As radiation emanates from exciting probe. 29, it will leak through the slits 32 and 33 in plates 26 and The slits are preferably aligned andv spaced outwardly in such manner that as radiation progresses through the outer atmosphere after having leaked through one of slits 33, it will be substantially in phase with radiation from the next outwardly located slit 33. A like spacing is observed. for slits 32. By this means the radiation emanating from theantenna assembly illustratedin Figs. 4 and 5 is given a sharply directive effect in the vertical plane. Due to the general symmetry of the structure about the vertical axis, radiationv will be generally non-directive in the horizontal plane, or any plane parallel thereto.

Although the descriptionherein with regard to the embodiments illustrated has been confined generally to consideration of radiation therefrom, like directive effects will be experienced when the antennaeare used for reception, as is well knownin the art. Therefore, it is not desired to restrict the invention by the discussion of such radiation effects. Furthermore, for the sake of simplicity, no impedance matching devices have been illustrated in the drawings in combination with the invention. Such devices might consist of adjustable, or adjusted stubs,

plungers, windows, or oi the other well know e ises uti gene al ii r: h pose.

Numerous variations will be apparent to those skilled in the art. Therefore, it is not desired to restrict the scope of the claims to the precise embodiments, herein disclosed.

W at sfl med. s;

1;. In an antenna, the combination of an enclosed transmission line, an array of dipoles aligned. substantially coaxially around said line and adapted to be excited by energ therefrom, andfa disk of material refractive to electromagnetic radiation supported by said transmission line and enclosing substantially coaxially, and symmetrically said dipole array. the thickness of said disc diminishing from the center to the edge.

2. In an antenna, the combination of an enclosed transmission line, a probe adapted to be electrically excited. from said transmission line, two metalli substantially plane circular plates forming. a, wave guide for energy radiated from said probe, a. disk of material refractive to. electromagnetic radiation enclosing said probe, the faces of. said. disk being at least partially enclosed by said plates, said plates, said disk, and said probe being. substantially coaxial.

3. In an antenna, the combination of an enclosed, transmission. line, a probe adapted to be excited. by. said transmission line, a disk of materialre fractive to electromagnetic radiation en.- closing said probe coaxially, twocircular con: verging plates substantially, enclosing said disk and. having slits. spaced. and arranged so that radiation, leaking. therefrom at the operating frequency is in phaseat. theperiphery of said plates, said plates, said disk, and. said probe being, subs e fia l o xi'e 4. In an antenna, thecombinationof radiating means adapted to produce nonrdirectional radiation. in a. plane perpendicular to a chosen axis, a disk of material refractive to electromagnetic radiation. substantially coaxial with said axis and enclosing said radiating means, saiddisc diminishing thickness from the center to. the edge.

HEN J R B ET REFERENCES CITED The following references are of. record in the file of thispatent;

UNITED STATES PATENTS Number Name Date 2,161,292 Hahnemann June 6, 1939 2,202,380 Holln ann May 28, 1940 2,206,923 Southworth July 9, 1940 2,283,568 Ohl May 19, 1942

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