A Pair-Centric Phased-Array Antenna Enabled by Reciprocity-Based Mode Separation for In-Band Radiation and Scattering

Low-observable phased-array antennas face a fundamental difficulty in jointly achieving in-band co-polarized scattering suppression, preserved radiation, and scalable array implementation. Element-level approaches often neglect coupling effects or rely on bulky loading structures, whereas full-array optimization is usually computationally intensive. This article presents a pair-centric design paradigm, in which a compact antenna pair (0.33λ \,×\, 0.31λ ~×\, 0.02λ) is used as the basic building block for integrated in-band radiation and scattering control. A reciprocity-based mode-separation framework is developed to guide the design by exploiting the asymmetric responses of odd and even mode spaces under offset port and normal-incident plane-wave excitations. This framework reveals that pattern restoration, port decoupling, and in-band scattering suppression can be achieved in a unified manner. Based on this concept, the optimized pair is extended to linear and planar arrays through pair-level beamforming under large-spacing array arrangements. Simulated and measured results demonstrate more than 20 dB in-band co-polarized RCS reduction under normal incidence, together with port isolation exceeding 20 dB and wide-angle scanning up to 86° for the experimentally validated 1-by-8 linear array; the scalability to the 8-by-8 planar array is further demonstrated by full-wave simulation. These results verify, in a proof-of-concept manner, the feasibility of integrating radiation and scattering control within pair-centric phased arrays.