The sensor circuitry is simple circuit, which detects if the mobile phone receives any message signal.
this is required, as the phone has to be charge as long as user is talking.
thus a simple F to V convertor would serve our purpose.
In India the operating frequency of mobile phone operators is generally 900 MHz od 1800 MHz for the GSM system for mobile communication.
thus the use of simple F to V would act as a switches to trigger the rectenna circuit to on.
LM-2907- a simple n F to V converter use as it operates between this specified rang.
Thus on the reception of the signal the sensor circuitry directs the rectenna circuit to ON and the mobile phone begins to charge using the microwave power.