A Compact 3-D Harmonic Repeater for Passive Wireless Sensing

A high-efficiency 3-D harmonic repeater for narrow band, wireless sensing applications is described herein. This repeater consists of a diode doubler and conjugate-matched 3-D receive and transmit antennas. The antennas are designed on the surface of a cube in part to provide a convenient volume for packaging the sensor electronics. The device operates by receiving a 2.4-GHz signal and re-radiating a 4.8-GHz signal and has been optimized for an RF input power level between - 30 and -20 dBm with zero dc power. The design enables the return signal to be readily modulated with very low ( <; 0.1 V) voltages. The diagonal of the entire repeater measures 0.24 λ at the fundamental frequency of 2.4 GHz, and its measured conversion gain is -13.3 dB with a 2.5% 3-dB conversion gain bandwidth at -30-dBm input power. Given this performance, the expected communication range using a 2-W source is >; 50 m in a free space environment. To the best of the authors´ knowledge, the presented harmonic repeater has the best overall performance among previously published designs, in terms of conversion gain, communication range, and occupied electrical volume. A new approach for remote calibration of passive sensors using orthogonal polarization of the interrogation signal is also proposed in this paper.