Wideband and Efficient Slot Cavity Backing for Unidirectional Log-Periodic Antenna

A slot cavity backing for unidirectional log-periodic (LP) antennas is proposed. Bowtie slot is etched on the bottom of a cavity to mitigate the degradation in impedance match at low frequency band of an LP antenna. The impedance match is further improved, and backward radiation is suppressed by resistively loading the slot. For conformal mounting of the antenna, an additional cavity with ferrite loading is attached to the bottom of the slot layer. Additionally, the slot termination is reengineered to enable recycling of the coupled power into the slot. The unidirectional LP antenna with the proposed cavity backing is prototyped and measured. The proposed antenna achieves VSWR below 3:1 from 0.5 to 5 GHz and below 2.5:1 from 0.64 to 5 GHz. The gain is higher than -2.9 dBi over 0.5 to 5 GHz (above 5 dBi from 1.5 GHz). Considerable improvement in gain and efficiency compared to a conventional ferrite-loaded cavity is demonstrated, while recycling option if exercised may further improve the system efficiency.