Performance Enhancement of Broadband Circularly Polarized Slot–Microstrip Antenna Using Parasitic Elements

In this letter, two novel broadband circularly polarized slot-microstrip antennas (SMPA) with circular and square structures are elaborated. The circular SMPA is composed of four crown patches as parasitic elements, four crown slots etched on a circular ground plane, and a circular loop sequential phase feeding structure. However, the square SMPA consists of four parasitic rectangular patches, four square slots with cut corners, and a square-loop feeding structure. In the circular SMPA, the parasitic crown patches and crown slots are used to excite multiple circularly polarized (CP) resonant modes, which are fed by a circular loop sequential phase feeding structure through capacitive coupling. Combined with these CP modes, the CP bandwidth of the presented antenna could be improved. Eventually, the proposed circular SMPA has a broad 3-dB axial ratio bandwidth (ARBW) of 20.6% (5.206.40, 5.8 GHz) and a wide 10-dB impedance bandwidth (IBW) of 25.8% (4.926.38, 5.65 GHz), which could occupy the WLAN (5.7255.85 GHz), ITS (5.8 GHz), and WIFI (5.85-5.925 GHz) bands.