Integrated Shared-Aperture Transmitarray Antenna With In-Band and Out-of-Band RCS Reduction

This paper presents an integrated shared-aperture transmitarray (TA) antenna that achieves a low radar cross section (RCS) at both in-band and out-of-band frequencies, while maintaining wideband beam convergence. The element employs a four-layer metallic structure: Cross-shaped patches and bent metallic strips are integrated on the top layer in a shared-aperture configuration, enabling independent reflection phase control across three distinct frequency bands; the middle two V-slot ground layers enable 1-bit transmission phase modulation via geometric rotation; and the bottom layer employs cross-shaped patches to ensure good radiation. Owing to the integrated design of the top-layer multi-band RCS reduction structures, the TA has a thickness of only $0.28\lambda _{c}~(\lambda _{c}$ denotes the wavelength corresponding to the center frequency). A $16\times 16$ prototype is designed, fabricated, and measured. Measurement results demonstrate a peak gain of 20.46 dBi at 13.75 GHz with an aperture efficiency of 20.8% and 1-dB gain bandwidth of 8.96%. Furthermore, the proposed TA antenna achieves a 10 dB monostatic RCS reduction over bandwidths of 23.66% (8.2 to 10.4 GHz) and 12.69% (15.5 to 17.6 GHz), with a maximum in-band (12 to 14 GHz) reduction of 16 dB compared to the reference TA antenna.