Multiple-beam Cassegrainian antenna

Claim 2

A multiple beam antenna comprising a main reflector having an aperture, a smaller subreflector, said antenna having an on-axis focal point lying outside the aperture, a plurality of means for feeding energy toward the subreflector, at least one of the feeding means being displaced from the on-axis focal point, the subreflector having a surface area elongated to avoid spillover in each direction corresponding to the displacement of a feeding means from the on-axis focal point, the feeding means and the subreflector being positioned so that they lie outside the aperture of the main reflector and center the energy from each feeding means on the main reflector, the subreflector reflecting energy from the feeding means directly to the main reflector.

Claim 3

An antenna as claimed in claim 1 wherein the reflectors are arranged to form a Cassegrainian antenna and the plurality of feeding means are clustered about the on-axis focal point of the Cassegrainian antenna.

Claim 4

An antenna as claimed in claim 2 further including a focal feeding means located at the on-axis focal point for feeding energy toward the subreflector.

Claim 5

An antenna as claimed in claim 2 wherein the surface of the main reflector is essentially paraboloidal and the surface of the subreflector is essentially hyperboloidal, and the feeding means are feed horns.

Claim 6

An antenna as claimed in claim 2 wherein the plurality of feeding means are displaced from the on-axis focal point along an essentially straight line through the on-axis focal point and the subreflector has an essentially oblate boundary having its longer axis in the direction of the straight line.

Claim 7

An antenna comprising a main reflector, a smaller subreflector, the subreflector being positioned to redirect radiation incident upon it toward the main reflector, said reflectors being positioned to form a Cassegrainian antenna, primary feed means located at the on-axis focal point of the Cassegrainian antenna for feeding energy toward the subreflector and the main reflector causing radiation emanating from it to form a main beam which passes through an antenna aperture, characterized in that the subreflector and said primary means for feeding energy are located outside said aperture, said antenna further comprising at least one secondary means for feeding energy toward the subreflector, said secondary means for feeding energy being located remote from the on-axis focal point and being aimed toward the subreflector so that the center of its beam impinges upon the main reflector at a center point common to the center of the beam generated by the primary feed means, the subreflector being enlarged in area so that spillover from the secondary means is avoided.

Claim 8

An antenna comprising a main reflector, a smaller subreflector, the subreflector being positioned to redirect radiation incident upon it toward the main reflector, said reflectors being positioned to form a Cassegrainian antenna, primary feed means located at the on-axis focal point of the Cassegrainian antenna for feeding energy toward the subreflector and the main reflector causing radiation emanating from it to form a main beam which passes through an antenna aperture, characterized in that the subreflector and said primary means for feeding energy are located outside said aperture, said antenna further comprising at least one secondary means for feeding energy toward the subreflector, said secondary means for feeding energy being located remote from the on-axis focal point and being aimed toward the subreflector so that the center of its beam impinges upon the main reflector at a center point common to the center of the beam generated by the primary feed means, the subreflector being enlarged in area so that spillover from the secondary means is avoided.

Claim 9

An antenna as claimed in claim 6 Wherein the surface of the main reflector is essentially paraboloidal and the surface of the subreflector is essentially hyperboloidal and the primary and secondary means for feeding energy are feed horns.

Claim 10

An antenna as claimed in claim 6 wherein the surface of the subreflector is essentially hyperboloidal and the boundary of the subreflector is essentially oblate, having its larger axis in the direction in which the secondary means for feeding energy is displaced from the on-axis focal point.

Claim 11

An antenna as claimed in claim 6 wherein the antenna comprises a plurality of secondary feeding means clustered about said on-axis focal point, each of the plurality being individually aimed toward the subreflector so that the centers of their beams impinge upon a common effective point on the main reflector but due to their displacement from the on-axis focal point radiate beams through the aperture having paths divergent from the axis of the main beam and from each other.