This report describes the fundamentals of the bridge RF rectifier with an impedance transformer. The rectifier allows full-wave-rectification with no additional circuit, enabling further downsizing and integration of the circuit. To improve the rectification efficiency, an impedance transformer is added between the input port and the bridge diode. From this configuration, we have derived rectification efficiency formulas showing that the design conditions of an impedance transformer are equivalent to the impedance matching conditions. We have assembled a trial circuit to verify the validity of the formulas and confirm improvements in the rectification efficiency with the impedance transformer. © 2011 IEEE.