Planar Ultrawideband Circularly Polarized Cosine Slot Archimedean Spiral Antenna for Partial Discharge Detection

Design and experimental verification of an ultrawideband planar circularly polarized ultrahigh frequency (UHF) sensor is presented for detection of partial discharge (PD) activities in high voltage (HV) equipment. The proposed sensor is cavity-backed cosine slot Archimedean spiral (CSAS) antenna with an electromagnetic (EM) transparent radome. The dual-arm slot spiral was meandered as cosine wave for size reduction and optimized for broadband operation with circular polarization (CP) over 0.5-5 GHz. Unidirectional radiation pattern with CP was achieved over 0.5-5 GHz using an optimized cavity loaded with EM absorber. The fabricated UHF CSAS sensor has the widest operating bandwidth of 0.5-5 GHz with circular polarization and the smallest aperture of 0.26 lambda(L) when compared to the existing UHF PD sensors, where lambda(L) is the wavelength at the lowest operating frequency. Time domain incipient discharge signals and phase resolved PD patterns gathered for three commonly occurring defects in test cells mimicking gas insulated switchgear (GIS) indicate better sensitivity and detection capability for the fabricated CSAS UHF sensor than the reference PD sensor. PD signal measurements and comparison with other UHF PD sensors indicate that the proposed UHF CSAS sensor could be used for PD detection in HV equipment.