Impedance-Synthesized In-Band RCS Reduction for Ultrawideband Phased Array Antennas via Field–Circuit–Structure Co-Design Approach

Achieving in-band radar cross section (RCS) in ultrawideband (UWB) phased array antennas (PAAs) is fundamentally constrained by the intrinsic coupling between radiation and scattering. This article presents a field–circuit–structure co-design approach for dual-polarized in-band RCS suppression in UWB PAAs. Impedance-synthesized cancellation radiators with matched radiation and opposite phase co-polarized reflections are employed to induce backward destructive interference while preserving radiation performance. By integrating periodic slot-line theory with equivalent circuit model (ECM) method, a predictive topology–response mapping is established for the cancellation radiators, enabling fast, nonempirical optimization and efficient prediction of active VSWR and monostatic RCS with substantially reduced design time. Cross-polarized scattering is further suppressed through the complementary scattering behavior of open- and short-circuited antenna states. Finally, a monolithic, all-metallic stepped notches PAA prototype validates the approach, operating from 2.7 to 10.5 GHz, demonstrating continuous in-band co-polarized RCS reduction exceeding 7dB (3.0–9.3 GHz) and cross-polarized reduction exceeding 10dB (2.8–10.7 GHz), without degrading array gain or scanning capability. The proposed approach establishes a predictive, generalizable, and computationally efficient design framework for low-RCS UWB PAAs.