RF power meter using a self balancing calorimetric bridge arrangement

A radio frequency (RF) power meter comprises a calorimetric bridge 31 which includes two input ports 32, 33, one for an RF signal 30 and the other for a balancing signal 57. The balancing signal 57 is adjusted according to a feedback signal derived from the difference between the RF and balancing signals 40, 41. A compensating signal 60 is also derived which is applied equally to both input ports of the calorimetric bridge such that the sum of the power associated with the compensating signal 60, the RF signal 30 and the balancing signal 57, is a constant value. The temperature of the calorimetric bridge may be held at a constant value by means of an external heater arrangement 38, 39, 61 such that thermal transients are avoided. Periodic switching between an integrator 52 and an offset signal 54 can be used in conjunction with a sample and hold control loop 49, 50 to allow the meter to operate when the bridge is close to the balanced condition. The meter may be used to test radio communication equipment.