US2580921A - Radio reflector - Google Patents

Description

H. IAMS RADIO REFLECTOR Jan. 1, 1952 Filed Oct. 1, 1947 A T TO/WVE Y veni'ar:

Patented Jan. 1,1952

r RADIO REFLECTOR Harley lame; Venice, Califg assign'or to' -Radio -'Gorporation of- America, a corporation ofsDela- Application October 1, 1947, Serial No. 777,355

-Claims. l I1 This invention relates to reflectors for radiant aener-gysuchas radio waves and particularly'to Ldvicesi for reflecting iricidenfienergy;regardalesslof its. azimuth "of incidence; back'in'the di- .rection from which it comes. -pe'rformithis function to a limited extent have been knowri for many years, and have been used with radiant energy for signalling, as beacons .for... markingchannels, and as artificial targets .for. .radar. systems. "These, prior art reflector" ..;systems.haveggenerally been vof the typeiknown ..as.corner .rieflectors .or triple mirrors described inLU. -S.I Patent 1,384,014 to" Reginald AJ'F'essenden.

l Suchv reflectors. operate satisfactorily through .a limited range of ariglesfof incidence, lessthan 1.90 degrees, andmay be made to serve through- ..out a..full 360' degrees. by combining sever'alzrefiectors so'that their angular ranges of"effectivenessoverlap. However, a composite reflec- .:Another object is to provide a reflector 'offthe ,described type 'which presents. a substantially smooth outer surfacefthereby reducing wind loading and icing tendencies and the consequent design problems.

A further object is to provide an omnidirectional reflector whose response is uniform with respect to azimuth, having no peaks or nulls in various directions, and is substantially independent of reasonably large variations in frequency of the incident energy.

Still another object of this invention is to provide a reflector of the described type which is readily adapted to key or modulate characteristically the reflected signal for purposes of beacon identification, for example.

The invention will be described with reference to the accompanying drawing, wherein:

Figure 1 is an elevation, partly in section, of a reflector structure according to the present invention, and

Figure 2 is a view similar to Fig. 1 of a modification of the structure of Fig. 1.

Reflectors which Similar reference characters; are applied'i to similar elements throughout the .drawinga Referring to-Fig. 1,- a ball or sphere l 'of dielectric material is-surroundedat its equatorrby a band 3 of conductive =material$ Thei'sph'ere i -may be solid" and composed ot-polystyrene, asphalt, para-fin; Y sulfur '0r'- other insulating material; or may be a hollowshell-filled withiliquid "or -powdered= dielectric material. 1 The. radius-5 of the sphere is several wavelengths or more bt the longest waves whichare 'to bereflected. iThe band 3 has a-width of...about...one:;half. wave length or more, and maybe supported. onzthe sphere l by small spacersfi.

The spacing between. the surface ioizthersphere l and the band .idependsuponthedielectric constant or refractivexindexuof the materialvpcf the sphere; andis made such that parallel beams of radiation, such: as those represented ;by.;;:the lines 7 and 9 in Fig. 1, will, bezrefracted;,byxthe .sphereso 2.5.130 intersect, inuthe planes of. the

band 3,. as indicated at. the point ll. Thus-,;the

..band'.will bexon :or .near. the surfaceufortarrefractive index of about 1.8,. andwill :be outside or insiderthe surfaceforlower :or higher .-refractive indexes.

, .reflectionzoccurs at. the band andzthe ener y reaching its;.inner surface; ,asv-at .the..point:-

goes;.back through rtherisphere i. :z-Energy, ofrrelativel short:- wavelength such; :as ,light, mgayr'zbe reflectedspecularly from -theband 3.:;.:;In;thisacase each incident ray, such as the rays 1 and 9, has its counterpart in a reflected ray such as the rays 7' and 9'.

Even when the dimensions of the device are of the same order as the wavelength of the radiation, as is contemplated in application to radio waves, reflection from the band 3 may not be specular, but more or less diffuse. This does not prevent satisfactory operation, because substantially all of the energy reflected from the band 3 will nevertheless be intercepted by the sphere I and refracted to follow parallel paths back in the direction of incidence.

The device of Fig. l is particularly useful as a beacon, since it returns a large portion of the incident energy directly towards the source. Such beacons may be used for marking channels, runways, obstructions, etc. for radar equipped ships and aircraft. Their presence is by reflecting portions of the band l8.

indicated on the conventional radar display by unusually bright spots or pips which are visually distinguishable from the marks caused by reflection from the terrain or water surface.

In order to better distinguish beacons from each other and from other reflecting objects, they may be coded or made to reflect intermittently according to some prearranged schedule. Fig. 2 illustrates a preferred embodiment of a coded reflector. The equatorial band l3 comprises alternate segments l5 and I! of reflect,- ing and non-reflecting material respectively. The band l3, or the entire assembly including the sphere I, is rotatable about the polar axis l9. In the structure illustrated in Fig. 2, the sphere l is supported on a shaft 21 for continuous rotation by a motor 23.

The device of Fig. 2 operates in the directions in which the sphere is backed As the band rotates, reflecting portions I5 and non-re- :flecting portions I! will successively come into line with the incident rays, and reflection in any particular direction, '1. e. from and toward any particular source, will go on and off or blink. The relative lengths of periods of reflection and non reflection and their sequence are determinedb'y the relative widths of the portions 15 and I1.

I claim as my invention:

1. An omnidirectional reflector for returning radiant energy incident in a dielectric medium along a path substantially parallel with that along which it arrives at the reflector, independently of the azimuth of said path, comprising a spherical body of dielectric material having a diameter of at least several wavelengths of the energy to be reflected, and an equatorial band of conductive material concentrically surrounding said dielectric body and in a plane parallel to the direction of travel of the incident energy to be reflected, said band having a width of substantially one half the wavelength of the energy to be reflected, said reflector being immersed substantially entirely in said medium, the inner surface of said band being positioned at the loci of the focal point of said energy.

2. An omnidirectional reflector for radiant energy incident substantially in a plane and for returning said energy along a path substantially parallel with that along which it arrives at the reflector, independently of the azimuth of said path, comprising a spherical body of dielectric material having a diameter of at least several wavelengths of the energy to be reflected, and a like that of-Fig. 1 with the exception that reflection occurs only concentric equatorial band of conductive material substantially in said plane and surrounding said dielectric body and in a plane parallel to the direction of travel of the incident energy. the inner surface of said band being positioned at the loci of the focal point of said energy.

3. A reflector to reflect energy propagated in a surrounding dielectric atmosphere of refractive index of unity and comprising a spherical body of a material having a refractive index greater than unity and a concentric equatorial band of reflecting material, the inner reflecting surface of said band being positioned at the loci of the focal point of said energy surrounding said body, said body and band being mounted to be substantially entirely freely exposed to the surrounding dielectric medium, the inner reflecting surface, etc.

4. A radar reflector to reflect energy propagated in a .dielectric medium and comprising a spherical body of insulating material of dielectric constant different from said medium and a band of conductive material concentrically surrounding a central zone of said spherical body, the whole being mounted to be substantially entirely freely exposed to said surrounding dielectric medium, the inner surface of said band being positioned at the foci of energy incidentpparallel to the plane of said band and refracted by said body.

5. An omnidirectional reflector to reflect energy propagated in a dielectric atmosphere of refractive index of unity and comprising a lens in the REFERENCES CITED The following references are of record in the flle of this patent:

UNITED STATES PATENTS Number Name Date 888,056 Barney May 19, 1908 2,068,950 Hamilton Jan. 26, 1937 2,120,524 Luce June 14, 1938 2,133,615 Gerhard Oct. 18, 1938 2,155,092 Kaplowitz Apr. 18, 1939 2,212,110 Beuermann Aug. 20, 1940 2,455,469 Caspar Dec. 7, 1948

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