Theoretical Analysis and some Experiments on 2L-Type Twin Loop Antennas by Moment Method

Abstract

Twin loop antennas are most widely used for UHF TV broadcasting. Previous researchers analyzed them by assuming a sinusoidal current distribution. Others adopted the higher order expansion (Fourier series) of the current distribution, however, their analysis did not sufficiently explain the wide-band characteristics of this antenna.
This paper applied the moment method to a twin loop antenna with a reflector plate or a wire screen-type reflector plate. As for the input impedance, 2L-type twin loop antenna has reactance nearest zero (in case that l₁=0.15λ0), that is, the VSWR is nearly equal to unity. Also, satisfactory wide-band characteristics were obtained. The agreement between the measurement and the theory is quite good.
It will thus be possible in future to improve practical antenna characteristics based on the obtained results.