Patent ID: 8629771

Claim:
A device that relies on the transmission and/or receipt of a main electromagnetic signal that can be blocked by an object being placed in proximity to the device, the device incorporating a primary antenna for transmitting and/or receiving the main electromagnetic signal and a proximity sensor comprising: an oscillator; an antenna for transmitting and receiving electromagnetic signals located adjacent to the primary antenna; a directional coupler having a first port and a second port connected together by a main line and a third port and a fourth port connected together by a coupled line, the first port being connected to the oscillator, the second port being connected to the antenna of the proximity sensor, and the third port being connected to a detector and acting as an isolated port of the directional coupler when a transmit signal is supplied from the oscillator to the antenna of the proximity sensor along the main line and as a coupled port when a receive signal is supplied from the antenna of the proximity sensor to the oscillator along the main line; wherein the oscillator is controlled to provide a transmit signal to the antenna of the proximity sensor along the main line of the directional coupler and wherein the detector provides an alert indicating the presence of a blocking object if the magnitude of the power of the transmit signal that is reflected back to the antenna of the proximity sensor in the form of a receive signal exceeds a threshold.