Compact Broadband Circularly Polarized Microstrip Antenna With a Cross-slotted Ground Plane

In this work, a compact circularly polarized (CP) antenna fed by microstrip line is proposed to work at millimeter wave band. The single series feeding line coupling with cross-slots in the ground plane creates a phase difference and excites orthogonal modes for circular polarization. Sequential rotation of current excited on the surface of radiating patch broadens the axial ratio bandwidth compared with the traditional CP patch antenna. The proposed antenna covers an impedance bandwidth (|S11|<; -10 dB) from 25 to 36.58 GHz (37.61%) and a 3 dB axial ratio bandwidth from 30.8 to 36.13 GHz (15.92%). The gain is greater than 5 dBi over the band. The proposed antenna has the merits of low profile, wide axial ratio bandwidth, and high gain.