Patent ID: 7791354

Claim:
A system for monitoring impedance, the system comprising: a monitoring power coupling device comprising at least a first port, a second port and a third port; the monitoring power coupling device comprising a power splitter and combiner and being configured to divide power received at the first port between the second and third ports, the device further being configured at least partially to isolate the second port from power received at the third port and at least partially to isolate the third port from power received at the second port; an isolation between the second and third ports in the form of a ratio between a voltage at the third port and a voltage at the second port being a function of an impedance connected to the first port; the first port being connected to the impedance to be monitored; at least one of the second port and third port being connected to be driven by an alternating signal source; and the second and third ports being connected to a monitoring device for monitoring signals at the second and third ports, thereby to monitor the isolation between the second and third ports and hence impedance at the first port; wherein the power splitter and combiner comprises a hybrid comprising a transformer providing the first, second and third ports.