Transform feed for low sidelobe space-fed lens phased array antenna

This study explored the use of a two-dimensional transform feed to provide overlapped subarray illumination in an optically-fed active lens phased array. The feed forms a set of over-lapped subarray beams which illuminate the rear face of the array lens. The lens contains transmit/receive (T/R) modules (active lens) and/or phase shifters (passive lens) and front and rear face radiating elements. The multi-element transform feed is comprised of a beamforming network having N beamports and in series with each beamport is a time delay unit, phase shifter, and circulator. The feed time delay units and phase shifters provide wide bandwidth steering at the subarray level and frequency independent collimation of the subarray beams. A power divider provides the multiple beamport amplitude weights on transmit and an adaptive network sets the beamport amplitude and phase weights on receive. The summation of the beams at the rear face of the lens produces low sidelobe illuminations on receive and an efficient taper on transmit. A computer model was developed and has been used to perform design tradeoffs and to determine design parameter values.