Beam Reconfigurable Antenna Integrated with Passive Transmissive FSS Superstrate for Beam-Tilt Enhancement

Abstract

This work presents a 360° beam reconfigurable circular patch antenna integrated with a passive transmissive Frequency Selective Surface (FSS) to enhanced beam tilt performance at 3.5 GHz. The baseline antenna achieved full azimuthal coverage, but the beam tilt is limited to approximately ±24°-29° due to restricted phase gradient control by the parasitic elements. To overcome this beam tilt limitation, a nested-square transmissive FSS superstrate is introduced as a passive superstrate to reinforce the existing phase gradient and increase the beam tilt angle of the antenna. The optimized FSS unit cell provides high transmission (|S21| = -0.13 dB) and low reflection (|S11| = -40 dB) at the operating frequency. Parametric studies identify a 1×4 array positioned 8 mm above the antenna as the optimum configuration, resulting tilt enhancement to ±32°-34°, improved sidelobe levels (-6 to -7 dB), and stable gain (≈ 6.7-7.9 dBi). A prototype was fabricated and validated in an anechoic chamber, with close agreement observed between simulated and measured beam tilt angle, gain, HPBW, S11 and efficiency (> 87%). These results demonstrate that a passive transmissive FSS can reinforce parasitic-induced phase gradients and provide a compact, low-loss solution for sub-6 GHz 5G beam-tilting applications.