A Low-RCS Phased Array Antenna with 4 × 4 Butler Matrix and Frequency Selective Rasorber

Abstract

This paper presents a low radar cross section (RCS) phased array antenna developed for secure 5G communication in the n79 band (4.7 GHz). The array consists of 16 microstrip antenna elements configured as a 1 × 4 linear array of 2 × 2 subarrays, excited through a corporate powder divider to ensure uniform amplitude distribution. A 4 × 4 Butler matrix is employed as a passive beamforming network below the array structure, while a frequency selective rasorber (FSR) layer is introduced above the array configuration to suppress its out-ofband scattering response. The Butler matrix generates four orthogonal beam states (±9° and ±28°) with consistent gain and accurate beam pointing across the operating band. The integration of the 3 × 10 FSR unit elements above the radiating surface significantly reduces monostatic RCS while maintaining high in-band transmission and stable radiation characteristics for different beam directions. © 2026 European Association of Antennas and Propagation.