An Experimental Study of Performance Enhancement of Medium-Frequency Small Loop Antennas for Through-the-Earth at 350 kHz

This paper presents an experimental investigation into enhancing the performance of medium frequency small loop antennas for Through-the-Earth (TTE) communication at an operating frequency of 350 kHz. The proposed small loop antenna is designed to have a 1/50 wavelength for use in cave environments. The experimental setup comprises a transmitter system with a signal generator and an earth-grounded antenna, and a receiver system with a small loop antenna and a spectrum analyzer, which is tested by transmitting signals from the transmitter to the receiver at a surface testing location. To enhance the performance of the receiver antenna, we investigate the effect of increasing the number of antennas, from one to two and four elements, to determine the optimal array arrangement. The experimental results are evaluated based on received power and antenna impedance. Our findings indicate that using a 4x1 vertical array antenna with small loop antennas induces the highest currents from the earth and improves signal power reception by up to 11.6 dB compared to a single small loop antenna.