Design of Optimal Gain Mask for Phased Array-Fed Offset Reflectors

Abstract

In this paper, we propose a method to derive an optimal gain mask to enhance the aperture efficiency of phased array-fed reflectors (PAFRs). The optimal gain mask is obtained to uniformly illuminate the offset reflector’s surface. The optimal gain mask is derived based on the square of the distances from the feed antenna to each point on the offset reflector surface. To generate a feed pattern similar to the optimal gain mask, a $4\times 8$ array antenna is used as the feed antenna. Using this array antenna, beam synthesis is applied through the superposition of array patterns sampled at 1° intervals in both $\theta $ and $\varphi $ . In addition, to achieve sidelobe suppression, quadratic taper function is applied to the derived optimal gain mask. We then illuminate the reflector using three feed patterns: a synthesized beam based on the proposed mask, a synthesized beam following a cosecant-squared mask, and a single horn antenna pattern. In this case, the same quadratic tapering order of $N$ = 0.5 is applied to both the proposed gain mask and the cosecant-squared mask. The proposed method shows a bore-sight gain of 48.2 dBi and a sidelobe level (SLL) of −39.0 dB, representing improvements compared with the results obtained using the cosecant-squared-based pattern (47.5 dBi and −35.8 dB) and the horn antenna pattern (47.8 dBi and −34.0 dB). These results demonstrate that the proposed gain mask and beam synthesis method are effective in achieving high aperture efficiency and sidelobe suppression performance.