Target acquisition antenna

Claim 2

A target acquisition system adaptable for acquiring a target over an elevation angle range of 2 theta , comprising a reflector system for deriving a secondary pattern, said reflector system having boresight, azimuth and elevation axes and a focal point, a central feed having the radiation center thereof positioned substantially at said focal point, and a plurality of auxiliary feeds having the radiation centers thereof displaced from each of said axes, the centers of a pair of said auxiliary feeds being equally displaced above and below the elevation axis, means for exciting each of said feeds to illuminate said reflector system to derive secondary patterns having main lobes of substantially equal maximum amplitudes, shapes and beam widths, said beam widths being less than 2 theta , the maximum amplitude of the main lobe associated with the central feed being substantially aligned with the boresight axis, the apertures of said feeds and the relative spacings of the centers thereof in the direction of the azimuth axis being such that the amplitude at the crossover points between the lobes associated with the auxiliary feeds and the central feed is approximately equal to the amplitudes of the lobes associated with the auxiliary feeds at the angle 2 theta , wherein said exciting means includes means for exciting each of said feeds with a different frequency.

Claim 3

The antenna of claim 1 wherein each of said feeds has substantially the same aperture area and shape, the length of the radiating aperture of said central feed along the azimuth axis from the boresight axis being greater than the separation of the closest edges of the auxiliary feeds from the elevation axis.

Claim 4

The antenna of claim 1 wherein said exciting means includes means for exciting each of said feeds with a different frequency energy at a different time.

Claim 5

The antenna of claim 3 wherein each of said feeds has substantially the same aperture area and shape, the length of the radiating aperture of said central feed along the azimuth axis from the boresight axis being greater than the separation of the closest edges of the auxiliary feeds from the elevation axis.

Claim 6

The system of claim 1 wherein said reflector system is a Cassegrain reflector system including a hyperboloid subreflector having first and second foci and a paraboloid main reflector having a focal point coincident with the first of said Foci, said secondary reflector having an apex along said boresight axis and between said foci, said central feed being positioned at a point coincident with the second of said foci, each of said auxiliary feeds deriving a primary pattern having a longitudinal axis to intersect the boresight axis at a point between the apex and first of said foci.

Claim 7

The antenna of claim 5 wherein each of said feeds has substantially the same aperture area and shape, the length of the radiating aperture of said central feed along the azimuth axis from the boresight axis being greater than the separation of the closest edges of the auxiliary feeds from the elevation axis.

Claim 8

A target tracking and acquisition system adaptable for acquiring a target over an elevation angle range of 2 theta , comprising a reflector system for deriving a secondary pattern, said reflector system having boresight, azimuth and elevation axes and a focal point, a monopulse feed having the radiation center thereof positioned substantially at said focal point, and a plurality of auxiliary feeds having their radiation centers displaced from each of said axes, the centers of a pair of said auxiliary feeds being equally displaced above and below the elevation axis, means for exciting each of said feeds to illuminate said reflector system to derive secondary patterns having main lobes of substantially equal maximum amplitudes, shapes and beam widths, said beam widths being less than 2 theta , the maximum amplitude of the main lobe associated with the monopulse feed being substantially aligned with the boresight axis, the apertures of said feeds and the relative spacings of the centers thereof in the direction of the azimuth axis being such that the amplitude at the crossover points between the lobes associated with the auxiliary feeds and the monopulse feed is approximately equal to the amplitudes of the lobes associated with the auxiliary feeds at the angle 2 theta , wherein said exciting means includes means for exciting each of said feeds with a different frequency.

Claim 9

A target tracking and acquisition system adaptable for acquiring a target over an elevation angle range of 2 theta , comprising a reflector system for deriving a secondary pattern, said reflector system having boresight, azimuth and elevation axes and a focal point, a monopulse feed having the radiation center thereof positioned substantially at said focal point, and a plurality of auxiliary feeds having their radiation centers displaced from each of said axes, the centers of a pair of said auxiliary feeds being equally displaced above and below the elevation axis, means for exciting each of said feeds to illuminate said reflector system to derive secondary patterns having main lobes of substantially equal maximum amplitudes, shapes and beam widths, said beam widths being less than 2 theta , the maximum amplitude of the main lobe associated with the monopulse feed being substantially aligned with the boresight axis, the apertures of said feeds and the relative spacings of the centers thereof in the direction of the azimuth axis being such that the amplitude at the crossover points between the lobes associated with the auxiliary feeds and the monopulse feed is approximately equal to the amplitudes of the lobes associated with the auxiliary feeds at the angle 2 theta , wherein said exciting means includes means for exciting each of said feeds with a different frequency.

Claim 10

In a monopulse system for tracking a target employing a cassegrain reflector system including a hyperboloid subreflector having first and second foci and a paraboloid main reflector having a focal point coincident with said first of said foci, a monopulse feed being positioned at a point coincident with said second of said foci, each of said foci lying on the reflector system boresight axis, the improvement comprising: means for providing increased reflector system beamwidth for enabling said monopulse system to accomplish target acquisition without reducing effective antenna diameter, said means including a. a plurality of auxiliary feeds having their radiation centers slightly displaced in a predetermined manner from said reflector system boresight axis, and b. means for sequentially exciting each of said feeds with a different frequency.

Claim 11

In a monopulse system for tracking a target employing a cassegrain reflector system including a hyperboloid subreflector having first and second foci and a paraboloid main reflector having a focal point coincident with said first of said foci, a monopulse feed being positioned at a point coincident with said second of said foci, each of said foci lying on the reflector system boresight axis, the improvement comprising: means for providing increased reflector system beamwidth for enabling said monopulse system to accomplish target acquisition without reducing effective antenna diameter, said means including a. a plurality of auxiliary feeds having their radiation centers slightly displaced in a predetermined manner from said reflector system boresight axis, and b. means for sequentially exciting each of said feeds with a different frequency.