RETRODIRECTIVE BEAMS AND THEIR APPLICATION TO LOW SIDELOBE PATTERN SYNTHESIS IN SMALL PLANAR PHASED-ARRAYS

Beam synthesis remains one of the most difficult problems for an anten na array designer, this task being made more difficult when one limits the number of elements to a handful. Pattern synthesis in planar arra ys is often achieved by the sampling of a continuous aperture distribu tion at the element locations. In the case of arrays of limited number s of elements this produces errors that can unacceptably distort the r adiation pattern. When one also then considers the effects of mutual c oupling between the antenna elements, the application of ideal element weights derived in this way are no longer valid. In the paper a techn ique is presented, using the concept of retrodirective beams, that can achieve a low sidelobe beam from a continuous distribution on a circu lar aperture. The theory is then extended to include a planar array of antenna elements. This Is achieved by the addition of retrodirective beams to the uniform beam pattern of the array. Measured data is prese nted for a small planar array antenna using the derived method. A meth od for correction of the element weights, to minimise the effects of m utual coupling, producing low sidelobe radiation patterns is then appl ied. No knowledge of the antenna array's coupling coefficients are req uired.