OPTIMAL DESIGN OF ELECTRICALLY-SMALL LOOP RECEIVING ANTENNA

There is a large body of literature for electrically-small loop receiving antennas including more recent work in demagnetization effects for magnetic materials which are used for reducing antenna size. Optimal design of loop antennas requires understanding the electromagnetic principles and is limited by the accuracy of predicting the electromagnetic parameters (resistance, inductance, capacitance, effective permeability, sensitivity). We present the design principles for electrically-small loop receiving antennas including recommended formulas, a novel approach to optimal design and an application example for use in the VLF/LF band (1–100 kHz) for two different ferrite-core loop antennas including the optimum coil parameters. Using a ferrite magnetic core greatly complicates analysis and prediction of resistance, inductance, and sensitivity as a function of frequency due to the dependence on core material properties, core geometry, and wire coil geometry upon the core (capacitance is typically negligibly affected). Experimental results for the two ferrite-core loop antennas and an air-core loop antenna validate the optimal design approach with good overall agreement to theoretical prediction of resistance, inductance, and sensitivity. Discussion and comparison between air-core and ferrite-core designs demonstrate the trade-off between outer diameter, length, and mass vs. sensitivity.