A low-RCS phased array antenna with 4×4 Butler matrix and frequency selective rasorber

This paper presents a low radar cross section(RCS) phased array antenna developed for secure 5Gcommunication in the n79 band (4.7 GHz). The array consists of16 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-of band 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.