Differential-Fed Traveling Wave Loop Antenna with Resistive Loading for Spectrum Monitoring

In this paper, a traveling wave square loop antenna with resistive loading is proposed for achieving a directional radiation pattern in spectrum monitoring systems. The proposed antenna consists of a metal square loop, a printed circuit board (PCB) for differential feeding and a PCB for terminal resistor loading. A compact balun ADT4-6T+ and lumped LC matching networks are introduced to realize the differential feeding. The terminating resistor at the end of the feed network is capable of absorbing the reflected currents, and thus the traveling wave currents are generated within the square loop antenna and the directional radiation characteristic is obtained. A prototype with a perimeter of $0.8 \lambda_{H}$ is built and measured, where $\lambda_{H}$ is the wavelength at the highest frequency. The proposed antenna features a VSWR less than 2.5 and directional radiation characteristic from 5 MHz to 200 MHz, and it is suitable for VHF band spectrum monitoring applications.