Design of 24–40 GHz Ultra-Wideband Circularly Polarized Monopole Antenna with a Defected Ground Plane

A new design method for an ultra-wideband circularly polarized microstrip-fed monopole antenna with a ground defect is proposed in this paper. To achieve ultra-wideband circular polarization performance, a parallelogram-shaped ground defect is employed in the bottom layer. The analysis of the ultra-wideband axial ratio (AR) and the impedance bandwidth of the proposed antenna is performed both in the top and bottom layers. A semi-circular aperture is designed to achieve impedance matching in the 24–40 GHz frequency range. Then, the AR bandwidth is discussed considering the surface current distribution produced by the parallelogram-shaped ground defect to rote current in each orthogonal phase. A prototype of the proposed circularly polarized antenna with a 50% ultra-wide bandwidth (from 24 to 40 GHz), a 10-dB return loss, and a 3-dB AR was fabricated and measured.