A Combination of Transmission Line Models as Design Instruments for Electromagnetically Coupled Microstrip Patch Antennas in the 2.45 GHz ISM Band

Abstract

This communication presents an analytical framework that combines transmission line models for the design of electromagnetically coupled microstrip patch antennas for the 2.45 GHz industrial, scientific, and medical band. It provides initial values for all dimensions of the antenna, with measured resonance frequency errors below 6%. The initial design is optimized in two subsequent phases to center the resonance frequency and to increase the impedance bandwidth (BW), obtaining measured resonance frequency errors below 0.6% and BW enhancements of more than 1.2 times the original ones, respectively. The model has been validated with antenna prototypes based on rigid and textile materials, exhibiting excellent free-space measured BW of 4% and 5.12%, maximal measured gains of 4.28 and 7.33 dBi, and radiation efficiencies of 63.4% and 71.8%, respectively. Moreover, very stable on-body performance is obtained, with minimal frequency detuning when deploying the textile antenna on the human body. The measured maximum on-body gain for the textile antenna equals 5.5 dBi, with a simulated specific absorption rate of 0.323 W/kg at 2.45 GHz.