Abstract: The invention relates to an impedance adaptation control process in low noise reception chains and a miniature microwave thermometer of application of the said process. The process is used mainly in order to measure internal temperature by microwave thermography. The thermal radiation is picked up by means of an aerial (1) which provides a signal (2). This signal (2) is sent alternatively with a signal (5) coming from a standard source to a hyperfrequency amplifier (3) in order to compare the said signals (2,5) and to adjust the source (4) in consequence. According to the invention, in parallel, an additional impedance (15) is placed by intermittance in parallel to the input of the amplifier (3). By means of a synchronous detection (18) of the resulting signal (7), the impedance of the standard source (4) is adjusted so as to equal that of the aerial (1).

Abstract: A high impedance four wire temperature sensing system is comprised of a thermistor or other sensor and four leads such that a constant current is impressed on the sensor via two leads and the voltage across the sensor is read via the other two. The sensor and leads have microwave surface resistivity much higher than impedance levels in microwave ovens so that negligible microwave energy is coupled to the sensing system. The high resistance leads in a rigid probe to be inserted into the food and in a flexible cable are electrically conductive iron oxide magnetic tape or are deposited conductors.