Patent ID: 7369811

Claim:
An RFID interrogating device connected to an antenna, comprising: an RF transmitter configured to form a transmit signal; a first directional coupler configured to extract a first portion of the transmit signal; a vector modulator configured to adjust the first portion of the transmit signal in phase and amplitude to form a nulling signal; a second directional coupler configured to combine at least a portion of the nulling signal with a second portion of the transmit signal reflected from the antenna and at least a portion of a responding signal from an RFID tag received by the antenna, wherein the phase and amplitude of the first portion of the transmit signal is adjusted such that the nulling signal can be used to substantially cancel the second portion of the transmit signal reflected from the antenna; a detector configured to detect a feedback portion of a combined signal from an output of the second directional coupler; and a controller configured to receive an input signal formed from the feedback portion of the combined signal and to form at least one output signal based on the input signal, wherein the at least one output signal is used by the vector modulator to adaptively attenuate the first portion of the transmit signal and to adaptively change the phase of the first portion of the transmit signal.