Abstract: A microwave moisture sensor operates on the principle that an emitted microwave is attenuated in rotary resonance with water molecules. The microwave moisture sensor includes measurement and reference signal systems sharing a microwave oscillator, a detector and other components, means for calculating the ratio of the signals from the respective systems, and an AGC circuit means for keeping the reference signal from the reference signal system at a predetermined level, so that drifts of the microwave oscillator, detector and other components will be cancelled and thus increased measuring accuracy will result. Furthermore, the microwave moisture sensor measure the basis weight and temperature of a material being measured, and processes the measured values according to predetermined moisture percentages free from adverse influences of the basis weight and temperature and thus increase the degree of measurement accuracy.

Abstract: A microwave moisture sensor comprising a first transmission and reception system comprising first transmission and reception horn antennas disposed in confronting relation with respect to each other and with a movable sheet like measurand disposed therebetween; and a second transmission and reception system comprising a second transmission horn antenna for re-emitting a microwave, as received by the first reception horn antenna against the measurand, and a second reception horn antenna for receiving the microwave emitted by the second transmission horn antenna and having passed through the measurand. The antennas disposed on one side of the measurand are spaced from each other by a distance of n.lambda..+-..lambda./4, wherein n is an integer and .lambda. is the wavelength of the microwave, in a direction substantially perpendicular to the plane of the measurand.