On the Circularly Polarized Parallel-Plate Antenna

A circularly polarized (CP) broad-beam parallel-plate (PP) antenna is investigated. The difference between the phase velocities of two PP orthogonal modes is used to obtain CP fields. The two orthogonal modes are excited by an inclined slot fabricated on the ground plane that connects the two PPs. By tuning the slot length, the impedance can be easily matched. To reduce the cross-polarized fields, a modified CP PP antenna with semicircular plates is introduced. ANSYS HFSS was used to simulate the antennas and prototypes were fabricated to verify the simulations. Both the original and modified CP PP antennas have an overlapping antenna bandwidth of ~13.0% and an antenna gain of ~8 dBic. As compared with other broad-beam antennas, the two PP antennas have simpler and larger structures, easing their fabrications especially at millimeter-wave frequencies. A design guideline is developed.