Harmonic Balance/Full-Wave Analysis of Wearable Harmonic Transponder for IoT Applications

The article presents a novel design of a compact wearable harmonic transponder with double-plane symmetry, composed of a dual-band patch-type antenna loaded by an HSMS-2820 Schottky diode, operated as a proof of concept at ISM UHF 869 and 1734 MHz frequencies. The antenna is analyzed and optimized for a minimum ground plate size by means of the CST Microwave Studio electromagnetic simulator, and its reflection coefficient is incorporated into the equivalent circuit model for a combined harmonic balance (HB) and fullwave analysis using the AWR Microwave Office commercial simulator. The transponder performance, including the complex input impedance matching and conversion loss (CL) between the fundamental and second harmonic frequencies on the diode, was evaluated both in free space and when attached to a human muscle phantom. The total harmonic transponder CL, including diode CL, antenna transponder gains, and impedance mismatching, is 6.2 dB for an excitation power of -25 dBm at the antenna-diode interface. The measured reading distances are 9.0 and 8.8 m for equivalent isotropically radiated power (EIRP) = 20 dBm when the transponder is placed in free space and on the human body, respectively. As a means of machine-to-person communication, the transponder is suitable for the Internet of Things (IoT) concept, e.g., for the identification of pedestrians in traffic, i.e., in a complex environment with unwanted radiation clutter and multipath fading.