A Principle of a Hybrid Microwave Power Sensor Based on Thermometric Measurements

A new principle of sensor is proposed for determination of microwave power in planar structures, through the direct measurement of a temperature gradient in the substrate induced by the dissipation of the power in a resistive matched load. The nodal thermal simulation tool of the ESACAP™ program was used which helped to determine that this gradient is proportional to the dissipated power. It can be measured by two resistive microthermometers under the ground plane which also plays the role of shield. In a first step, a hybrid sensor was designed of intrinsic sensitivity S=45°C/W, for a power range of 10 mW‐375 mW, and for an ambient temperature which can vary between 10°C and 100°C ( the sensitivity variation is around 10 ppm/°C). A prohibitive 0‐95% response time of 650 ms was found.. Consequently, a simulation of a smaller size sensor (volume divided by 1000) was performed, which revealed a strongly reduced time constant (8.5 ms).