Design of a Circularly-Polarized UHF Antenna for Partial Discharge Detection

In this work, a circularly-polarized ultra-high frequency (UHF) partial discharge (PD) antenna is proposed to detect the PD in 0.6 GHz - 1.7 GHz. The proposed PD antenna consists of an Archimedean spiral antenna, a balun, and a cavity. The Archimedean spiral antenna is embedded by FR-4 as substrate and superstrate for miniaturization. The microstrip-to-paired strips balun is designed to yield good performance in the return loss, insertion loss, and amplitude and phase imbalances which are of great necessity for low axial ratio. The cavity is employed to obtain unidirectional radiation patterns and prevent external signal interference. However, it is found that the originally-designed cavity-backed antenna does not work properly near 1.35 GHz due to resonance phenomena in the cavity. In this work, the cavity is modified to tackle this problem. The proposed UHF PD antenna is fabricated and measured and the results show that it provides good impedance matching, realized gain, radiation pattern, and circular polarization.