Signal and noise analysis of a loop-monopole active antenna

Directional active antennas have been widely studied over the past decade. Most of the efforts have been experimental rather than analytical. The experimental work of Meinke led to the development of an electrically small loop-monopole active antenna suitable for direction finding. This paper shows that performance characteristics such as the noise figures and radiation patterns of the active loop-monopole antenna can be analytically predicted. The analytical techniques used involved the integral equation solutions by the moments method together with standard RF circuit analysis. The predicted results agreed quite well with measurements. Although the antenna is electrically small, any attempt to predict the antenna performance using only the circuit approach may not work, as the mutual coupling between the loop and monopole has a strong effect on both the signal and the noise.