There are three sensors in common use for instrument used to measure leakage power from microwave ovens. These are RF diodes, low mass thermistors and thin-film thermocouples. All have advantages and disadvantages and all must be configured such that they allow adequate speed of response, overload capability and the ability to respond within +/-1dB to plane waves of all polarisations.
RF diodes are perhaps the most commonly used device in cost effective microwave power flux density instruments used to measure oven leakage