Dual-Polarized Multi-Frequency Phased Antenna Array with Suppressed Higher Order Modes

Abstract

5G base stations operating in sub-6 GHz frequencies typically utilize full-dimensional or 3D beamforming with precise steering, using electronically scanned phased array antennas (PAA). Additionally, Radar systems for Defence applications in the S-band/sub-6 GHz use electronically scanned arrays for wide coverage. However, higher-order modes (HOMs) in these antenna arrays deployed in RF systems can lead to EMI/EMC issues and spurious harmonics. Furthermore, use of multiband PAAs can improve space utilization-efficiency and reduce cost. In this thesis, design of sub-6 GHz PAAs using dual-polarized mulit-band antenna elements having suppressed higher order mode (HOM) functionalities is explored. Initially, a 2×2 sub-array is developed for MIMO/phased array applications, which uses a square microstrip antenna with a mushroom unit-cell loading, achieving multi-band response in the sub-6 GHz band. Next, a sub-6 GHz 4×4 sub-array is developed using a microstrip patch antenna with complementary split ring resonator (CSRR) loading for simultaneous miniaturization and multi-band functionalities. The HOMs induced by the CSRR loading are further suppressed using a plated through hole (PTH). A beam steering range of ±40° is demonstrated in the designed 2×2 and 4×4 sub-array antennas. Finally, a single-layer, 64-element (8x8) PAA featuring dual-band, dual-polarization and HOM suppression is developed. The antenna elements with CSRR loading achieve dual-band dual-polarization performance at 3.45 GHz and 3.87 GHz, achieving gain of 23 dBi, while suppressing the HOMs using a PTH. The PAA prototype is fabricated, and its performance is validated through S-parameter characterization using Keysight PNA and beam-steering evaluation via near-field test range. The proposed PAA demonstrates beam steering range of ±60°, which is validated using both Ansys HFSS simulations and experiments on fabricated prototype using 6-bit phase shifters.