Microwave moisture sensor

Claim 1

A microwave moisture sensor for sensing moisture content in a sheet like measurand having a plane surface by measuring the attenuation of microwave passed through said measurand, comprising at least a first transmission and reception system for emitting a microwave against said measurand and receiving said microwave having passed through said measurand and being attenuated thereby, said first transmission and reception system comprising first transmission horn antenna and first reception horn antenna spaced in confronting relation with respect to each other by a constant distance, with said measurand disposed therebetween; a second transmission and reception system comprising a second transmission horn antenna disposed on the same side of said measurand in which said first reception horn antenna is disposed, for re-emitting said attenuated microwave as received by said first reception horn antenna against said measurand, and a second reception horn antanna spaced in confronting relation from said said second transmission horn antenna by said constant distance, for receiving said microwave emitted from said second transmission antenna and having passed through said measureand and being attenuated thereby, wherein the offset between antennas at the same side of the measurand, measured in a direction perpendicular to the measurand plane, is equal to an odd multiple of quarter lambda, wherein lambda is the wavelength of said microwave; and signal processor means for processing signals from said second reception horn with a preset signal indicative of the moisture basis weight of said measurand and predetermined moisture calibration data, thereby to generate a moisture percentage signal which is substantially unaffected by vibration of the measurand.