A Compact Dual-Channel Transceiver for Long-Range Passive Embedded Monitoring

A compact 3-D dual-channel transceiver for passive wireless sensor node design is described herein. The transceiver contains two harmonic repeaters, one to be connected to a sensor and one to provide a reference signal for remote channel calibration and node identification (ID). Each repeater consists of a diode-based frequency doubler and conjugate-matched receive and transmit meandered monopole antennas. The sensing repeater operates by receiving a 2.4-GHz signal and reradiating a modulated 4.8-GHz return signal. The reference and sensing repeaters are optimized for RF input power level ranges from -30 to -20 dBm with zero dc power. The diagonal of the transceiver measures 0.25 λ at the fundamental frequency of 2.4 GHz and its measured conversion gain (CG) is -12.4 dB with a 2% 3-dB CG bandwidth at -20-dBm input power. With this performance, the communication range using an interrogator with a 2-W effective isotropic radiated power is > 40 m in a free-space environment. To the best of the authors' knowledge, the presented transceiver is the first completely passive design with built-in passive remote channel calibration and ID capability. The performance and size of the proposed design compare well with previously published passive single-channel harmonic repeaters.