US2512139A - Antenna - Google Patents

Description

SPIN AXIS w. M. cADY ANTENNA Filed Dec. 29, 1944 FIG. 1.

no -1 REVERS/N WEC/#mun l June 20, 1950 SPIN a RADIATION-AWS FIG. 5. A

' INVENTOR.

WILLOUGHBY M. CADY BY Y ATTORNEY FIG. 4.

Patented June 20, 1950 ANTENNA f Willoughby M. Cady, Cambridge, Mass., assignor, by Ymesne assignments, to `the United States of America as represented` by War the Secretary `ci Y Application December29, 1944, Serial No. 570,413

This invention relates to directional antennas which are particularly applicable to radio direction-finding or object-location systems operating in the ultra high frequency region, or higher.

It is the object of this invention to provide a directional antenna so constructed and arranged that the .scanning pattern which is produced by the antenna can be readily changed merely by varying the rotative speeds of cert-ain elements.

For a ibetter understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in connection :with the accompanying drawing, wherein like parts are indicated by like reference numerals.

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

Fig. 2 is a diagrammatic view of the antenna, showing the components in different relative positions as compared with Fig. 1; and

Figs. 3, 4 and 5 are, respectively, diagrammatic views `of three different scanning patterns that can be obtained by means of the invention.

In Fig. 1 there is shown an antenna comprising a wave transducer, such as a dipole I0, situated substantially in the focal plane of a paraboloidal reflector I2 but displaced from the axis PA thereof. The reflector is mounted on a hollow shaft I4 which is adapted to be rotated by means such as shown schematically in Fig. 1 wherein a scanning motor II drives the shaft I4 through the medium of bevel gears I3 and I5. The axis of rotation, or spin axis of the paraboloid, indicated by the solid line SA, is disposed at an angle with respect to the parabo-loid axis PA.

Dipole I is mounted on a support I6 fastened to or integral with a rotatable shaft I8 extending through and coaxial with the shaft I4. The dipole support I6 and shaft I8 may form a part of the antenna feed, the portion I6 extending at an angle with respect to the spin axis SA. Shafts I4 and I8 are yadapted to be simultaneously rotated in opposite `or in the same direction, at the same or relatively different speeds. Any desired means for adjusting the relative speeds and direction of rotation of either shaft I4 or I8, or both, may |be utilized. For purposes of illustration, shaft I4 is shown as being driven by scanning motor II through the medium of bevel gears I3 and I5, and shaft I8 is shown as being driven by said scanning motor through the medium of bevel gears I'I and t9. Reversing mechanism 20 and change speed gear 2l are illustrated as providing means for respectively 6 claims. (cl. 25o-sassy determining the direction of rotation and/or .the speed of shaft. I8. Although meansv to adjust the speed and/or direction of rotation of only. shaft I8 is shown, it is to be understood thatsaidmeans may also be applied to change .the speed: and/0r direction of rotation of shaftv- I4, or oft both shafts. .i

In the example shown in Fig. 1, it will be as-.. sumedthat the spin axis SA is at an angle-0 with respect .to the paraboloid axis PA, and; the support it is at an --angle 20 with respect-tosaid spin axis. Itwill also be assumed that the dipole and reflector are rotating in opposite directions at the same speed. With the positions of the elements as shown, if specular reflection is assumed, the direction of maximum radiation RA will be at an angle of 30 from the parabolic axis PA, or 40 with respect to the spin axis SA. This angle is the maximum angle of reflection with respect to the spin axis. One-half cycle of rotation later, the relationship of the antenna elements will be reversed, so that the maximum angle of reflection will be at an angle 40 from the spin axis but in the opposite direction.

Fig. 2 shows the conditions existing onequarter cycle from the instant represented in Fig. 1. The drawing is taken through a plane at right angles to the plane shown in Fig. 1. Here the angular deflections of the respective axes relative to that of the spinner axis are the same as hown in Fig. 1, ibut the deflections are in the same sense. From this diagram, it can be seen that the radiated energy will be deflected an angle 6 with respect to the parabolic axis. This places the axis of radiation along the spinner axis so that the radiation is still in the same plane as that of Fig. 1. For intermediate positions between the two limits shown in Fig. 1 and Fig. 2, it will be found that the radiation is always in one plane, as indicated in Fig. 3. Such an arrangement is particularly useful for limited sector scanning.

If the two rotation rates are slightly different, the rosette pattern shown in Fig. 4 will result. In this case, the speed of rotation of the reflector I2 is either slightly faster or slower than the rotation of the feed I6. A conical scan may be afforded by maintaining one of the elements station-ary so as to obtain a circular pattern. If on the other hand one of the elements, instead of being fixed, is rotated slowly with respect to the other rotating element, a pattern such as shown in Fig. 5 will be obtained. This consists of a circular conical scan pattern wherein the center of the circle travels along an arcuate path,

Further variation may be afforded by rotating the elements in the same direction at diii'erent speeds, thus making it possible to obtain a spiral scan, for example. It will be obvious that the angular and speed relations of the rotating elements can be varied to provide other scanning patterns.

Whilethere hasbeenrdescribed what is at present considered a preferred embodiment of the '4 the rate of rotation of said reflector is greater than the rate of revolution of said transducer.

4. An antenna as set forth in claim 1, wherein the rate of rotation of said reiiector is less than the rate of revolution of said transducer.

5. A directional antenna Ycomprising a Wave transduceraand a paraboloidal reflector therefor, said` transducer being situatedin the vicinity of the focal plane of said reflector but displaced invention, it will be apparent to those skilled infilo from the axis thereof, means to rotate said the art that various changes and modifications may be made therein without departing from the spirit of the invention; hence.it.:is.not,intended 1 to limit the invention to theVprecise-detailsdisclosed herein but to cover al1 suchchanges 'and modifications as come within the purview 0f the appended claims.

I claim:

l. A directional antenna comprising -a wave transducer and a paraboloidal reiiector therefor, said transducer being :situated inxthe vicinity of thei focal plane .o `of Y. said ,i reiiector but' displaced from the axis thereof,meansto rotatesaidreflecton in onefdirectionfabout a-second axis which is disposedat-anangle mthrespectto the axis of the parabolcid;and meansI to revolve said transducer in an opposite direction about saidfsecond axis.

`-2`. Anqantenna asset forth `in claim-l,- wherein the rate: of L`rotationA of said reflectoris equal to therate1of revolution of -said-1 transducer.

23. An antenna asset-forth `in claim 1, `wherein .reflector about a second axis which is disposed at an angle with respect to the axis of the paraboldi-mand'. means. to revolve said transducer rel- -ative.to. saidreeetor about said second axis.

6. A-directionalantenna comprising rotatable radiating and reecting elements, and means adaptedto rotatesaid elements in opposite directions during scanning.

WILLOUGHBY M. CADY.

REFERENCES 3 GITED The following references are of record' inl the le of vi'.hisp:a.tent:

UNITED -SIATES PATENTS Number Name kDate `1,931,980. Clavier Oct. x24, 1933 2;()835-242 IRunge June 8,1937.

VFOyIitEIGN PATENTS.

Number Country Date 4505484 .zGreatfBritain July l2O,'I|;9,3Ei

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