Multibeam antenna arrangement with minimal astigmatism and coma

Claim 1

A multibeam antenna arrangement with minimal aberrations due to astigmatism and coma, comprising: a plurality of N sequentially confocal reflectors including N+1 separate focal points comprising at least a curved focusing offset main reflector capable of bidirectionally reflecting a beam of radiated electromagnetic energy between the N th and the N+1 focal points along a feed axis thereof, and a subreflector disposed along the feed axis of the main reflector comprising a curved reflecting surface capable of bidirectionally reflecting said beam between said N th and an N-1 points of the N+1 separate focal points; and at least one feedhorn disposed at or in the vicinity of a first focal point of said N+1 focal points and oriented with a longitudinal axis thereof coincident with an equivalent axis of the plurality of N sequential confocal reflectors, the equivlent axis being an axis of revolution which passes through the first focal point of an equivalent reflecting surface which is capable of producing after a single reflection the same field distribution over the reflected wavefront as that of the plurality of N sequential confocal reflectors characterized in that the reflecting surface of each of two of the plurality of N sequential confocal reflectors are deformed with a separate deformation coefficient, C n specifying the displacement, Z n , of each associated reflecting surface in the Z th direction according to the relationship Z.sub.n =C.sub.n P.sub.n where P n is the distance from the Z axis at a focal point of the reflector, and the deformation coefficient for each of the two reflecting surfaces is specified by the relationship ##EQU6## where the magnification of any reflector ##EQU7## with l 2n-1 and l 2n-2 being the distances along the feed axis of the antenna arrangement to a central point on the reflector from the focal point of the reflector nearest and furthest, respectively, from the first focal point of the antenna arrangement; n 1 and n 2 designate the number of the nearest and furthest reflector, respectively, along the feed axis from the first focal point of the antenna arrangement to be deformed; i is the angle of incidence of a ray propagating between the two focal points of a reflector which impinges the central point of the reflector n; (M n .sbsb.1 +1 . . . M n .sbsb.2) represents the product of the magnifications of the reflectors n 1 +1 to and including reflector n 2 ; M is the total magnification of the antenna arrangement; and (M 1 . . . M n .sbsb.2) is the product of the magnifications of the first reflector up to and including the n 2 reflector of the antenna arrangement.