Adaptive power controllable retrodirective array system for portable battery-operated applications

An adaptive power controllable retrodirective array system is presented for portable applications. The proposed system is able to turn on only when it needs to operate so that it can avoid wasting battery power in idle mode. This power management is accomplished by employing a rectenna and an analog switch into a battery-operated system. When an RF signal is received by an antenna, it is divided into a rectenna and a receiver, where most power is sent to a rectenna through a 15-dB coupler. The converted DC power from a rectenna wakes up the system by activating a switch connected to a battery and the receiver. When there is no interrogation, a switch becomes off. An output voltage is twice increased by a voltage doubler and added up by connecting in series. The 2nd and 3rd harmonic rejection characteristic of a circular sector antenna is introduced so that it makes the system simpler by eliminating a low-pass filter (LPF) in the rectenna. For the phase-conjugation retro directive array, 2nd sub-harmonic mixers are used by employing anti-parallel diode pairs (APDPs), which enables to avoid the 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 density is over 0.057 mW/cm².