“Improved” Calculation of Reflection Coefficient for Coaxial Antennas With Feed Gap Effect

A method is proposed to characterize the reflection coefficient of an insulated coaxial antenna with consideration of the feed gap effect. This method models the insulated antenna as a transmission line and extends the method proposed by Su and Wu . The original model assumed the gap to be small and considered a simple capacitance which is ignored in the calculation. Our improvement to this model is a component added to account for the gap impedance. When using insulated dipoles in medical treatment (hyperthermia, ablation, etc.), optimized antennas may require larger gaps, which this ldquoimprovedrdquo model accounts for. Excellent agreement is observed between theoretical and numerically simulated S ₁₁ data, which indicates that this is an appropriate model for designing an efficient applicator for interstitial microwave hyperthermia.