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

Abstract

In this letter, two novel broadband circularly polarized (CP) 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, and a circular loop sequential phase feeding structure (SPFS). However, the square SMPA consists of four parasitic rectangular patches, four square slots with cut corners, and a square-loop SPFS. In the circular SMPA, the parasitic crown patches and crown slots are used to excite multiple CP resonant modes, which are fed by a circular loop SPFS 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 of 20.6% (5.20–6.40, 5.8 GHz) and a wide −10 dB impedance bandwidth of 25.8% (4.92–6.38, 5.65 GHz), which could occupy the wireless local area network (5.725–5.85 GHz), ITS (5.8 GHz), and WIFI (5.85–5.925 GHz) bands.