A Sidelobe-Reduced Wideband Flat-Gain Low-Profile Transmitarray Using a Simple Amplitude Control and Phase Error Compensation

This article proposes a novel design of a double-layer transmitarray (TA) antenna featuring sidelobe level (SLL) suppression, wideband flat gain, and a low-profile structure. First, a simple amplitude method is proposed to achieve the Taylor distribution by optimizing the focal-to-diameter ( $F/D$ ) ratio, which effectively suppresses the SLL of the TA antenna. Compared to conventional methods that require individual adjustment of the transmission amplitudes for numerous unit cells, this novel strategy greatly simplifies the design process, avoiding structural complexity. In particular, the optimal $F/D$ ratio is much smaller than traditional values, resulting in a substantially reduced profile. Second, by determining the optimal phase compensation frequency, phase errors can be introduced at each frequency point. This allows for the reduction of gain across all frequencies to varying degrees, thereby achieving flat gain over the desired frequency range. Notably, this method eliminates the need for the complex algorithms typically used in conventional approaches. To validate these methods, a wideband double-layer TA prototype combining both approaches is fabricated and tested. The optimal $F/D$ ratio is determined to be 0.33, resulting in an overall profile of $2.52\lambda _{0}$ . The radiation patterns demonstrate a 1-dB bandwidth (BW) of 27.3% and the lowest SLL of −20 dB. To our knowledge, this represents the first double-layer TA antenna that successfully implements amplitude control within a low-profile structure while achieving flat gain over a wide frequency range.