Adaptive power controllable retrodirective array system for wireless sensor server applications

An adaptive power controllable retrodirective array system is presented. It is able to conserve battery power in an idle mode and wake up only when it needs to operate, extending the array system's lifetime. One application of this technology is for use as wireless sensor servers, which act as a relay point between wireless sensors and remote data collectors. The proposed retrodirective array is fabricated and tested at 5.8 GHz and uses an integrated rectenna and an analog switch, which controls a battery power source. When an RF signal is received by the antenna array, it is split between a rectenna and receiver (RX), where most power is sent to a rectenna. The collected dc voltage wakes up the system by activating a switch connected to a battery and the RX. When there is no interrogation, the switch turns off. Furthermore, the second and third harmonic rejection characteristic of a circular sector antenna is introduced so that it makes the system simpler by eliminating a low-pass filter in the rectenna. For the phase-conjugation retrodirective array, second subharmonic mixers are used by employing antiparallel diode pairs, which enables avoiding expensive high-frequency oscillators. It is experimentally demonstrated that the retrodirective array system with the proposed power management can retransmit the received signal toward the source when the received power is greater than -8.5dBm. Application of the retrodirective array system as a multifunctional RX array is also investigated.