Wideband Low-Profile Ka-Band Microstrip Antenna with Low Cross Polarization Using Asymmetry AMC Structure

In this work, a 28GHz microstrip antenna based on an asymmetric artificial magnetic conductor structure is proposed, which takes the features of low profile, high bandwidth, high gain, and low cross-polarization level. The principle that the AMC structure servers as a reflection plane of the microstrip antenna to widen bandwidth is deeply investigated. The mechanism of the H-plane cross-polarization level deterioration when the symmetric AMC structure is applied to the microstrip antenna is analyzed for the first time. The asymmetric AMC cell provides a 0° reflection phase for the E-plane horizontal electric field and a 180° reflection phase for the H-plane horizontal electric field. Therefore, it is used as a reflection plane to achieve both large bandwidth and low cross-polarization level. The simulation results demonstrate that the proposed antenna with 0.056λ
₀
substrate thickness realizes the high bandwidth of 23% and low H-plane cross-polarization level of less than -20dB in band. The radiation efficiency is up to 97.6% at 27GHz while peak gain reaches to 10.1dBi at 31.2GHz.