Waveform design for rf power transfer

A passive tag transponder circuit, comprising:

• a receive antenna configured to receive an ambient RF signal having a frequency of fc, or, to receive a backscattered RF signal having a frequency of 2fc;
• a rectifier network;
• and
• a reflect antenna configured to receive a rectified output signal from a rectifier network, the rectified output signal having a frequency of 2fc and configured to send a backscattered signal at the frequency of 2fc, wherein:
• the rectifier network is connected to receive an input corresponding to the ambient RF from the receive antenna and send the rectified output to the reflect antenna, and
• the ambient RF signal has a modified continuous waveform such that the rectified output has substantially no harmonic frequencies greater than 2fc.