Towards High-Performance Reflectarray Antennas: Phase Sensitivity Reduction for Wide Bandwidth

Abstract

Reflectarray antennas are gaining popularity in satellite and communication systems due to their high gain and lightweight design. However, their limited bandwidth poses a significant challenge because phase behavior varies across different frequencies. This thesis aims to address this limitation by proposing methods to widen the bandwidth while maintaining antenna performance. The research begins with an exploration of various bandwidth-enhancing techniques, such as air gaps and multi-resonant elements. An initial design of a reflectarray antenna was introduced and simulated using a Jerusalem cross-shaped unit cell. While promising, this design highlighted the necessity for a deeper understanding of the field behavior within the unit cell. Thus, the focus shifted to a rectangular dielectric resonator unit cell, which offers more precise insights into resonance modes and their effects on antenna performance. A detailed analysis of the resonant modes within the dielectric resonator unit cells was conducted. By identifying and controlling unwanted resonances that contribute to phase variation, the reflection phase can be stabilized over a broader frequency range. This significantly increases bandwidth without compromising the antenna’s gain or efficiency. Two reflectarray antennas were designed and simulated to validate the proposed methods: a linearly polarized antenna with a rectangular dielectric resonator unit cell and a wideband circularly polarized antenna using a cross-shaped unit cell. The simulations employed two full-wave electromagnetic tools: High-Frequency Structure Simulator (HFSS) and CST Studio Suite. The results were promising; the wideband dielectric reflectarray antenna achieved a 26.6% 1 dB bandwidth and a 60% 3 dB bandwidth, with an aperture efficiency of 55% at the center frequency and a maximum gain of 30 dB. The circularly polarized reflectarray for Ka-band applications demonstrated a 33.3% 3 dB axial ratio bandwidth and a maximum gain of 28 dB. The simulation results showed strong agreement, validating the proposed approach. In conclusion, this thesis presents a method to reduce phase sensitivity within unit cells, a critical factor for achieving wideband reflectarray antennas. By maintaining uniform reflection phase across frequencies, bandwidth and overall performance are significantly enhanced.