Microwave moisture measuring apparatus

Claim 2

Microwave moisture measuring apparatus including in combination a variable frequency source of microwave energy, control means for cyclically varying the frequency of the source, means including a lens-corrected horn for radiating energy from the source through a moisture containing material, said material attenuating the energy passing therethrough as a function of its moisture content, a first detector, and means coupling both the source and the attenuated energy to the first detector.

Claim 3

Apparatus as in claim 1 further including a band-pass filter, a second detector, and means including the filter for coupling the first detector to the second detector.

Claim 4

Apparatus as in claim 1 wherein the control means cyclically varies the source frequency at a certain repetition frequency, the apparatus further including an amplifier, a band-pass filter, a second detector, means including the amplifier and the band-pass filter for coupling the first detector to the second detector, a low-pass filter, and means coupling the second detector to the low-pass filter.

Claim 5

Apparatus as in claim 3 wherein the low-pass filter has a cut-off frequency less than twice said repetition frequency.

Claim 6

Apparatus as in claim 1 wherein the construction of the control means is such that the source frequency cyclically varies in accordance with a generally triangular waveform having equal positive and negative slopes.

Claim 7

Apparatus as in claim 1 wherein the construction of the control means is such that the source frequency cyclically varies in accordance with a trapezoidal waveform having flat top and bottom portions of appreciable extent.

Claim 8

Apparatus as in claim 1 wherein the means coupling the attenuated energy to the first detector includes a delay line.

Claim 9

Apparatus as in claim 1 wherein the means coupling the source and the attenuated energy to the first detector includes a directional coupler.

Claim 10

Apparatus as in claim 1 wherein the radiating means includes a microwave isolator.

Claim 11

Apparatus as in claim 1 wherein the means coupling the attenuated energy to the first detector includes a microwave isolator.

Claim 12

Apparatus as in claim 1 wherein the radiating means includes means for passing source energy twice through the material.

Claim 13

Apparatus as in claim 1 wherein the radiating means includes a first transmitting horn antenna disposed on one side of the material, a first receiving horn antenna disposed on the other side of the material and oriented to receive energy from the first transmitting horn, a second transmitting horn antenna disposed on said other side of the material, means coupling the first receiving horn to the second transmitting horn, and a second receiving horn antenna disposed on said one side of the material and oriented to receive energy from the second transmitting horn.

Claim 14

Apparatus as in claim 12 wherein the means coupling the first receiving horn to the second transmitting horn includes a delay line.

Claim 15

Apparatus as in claim 1 wherein the radiating means includes a first and a second horn antenna disposed on opposite sides of the material and oriented to transmit and receive energy from one another, a first and a second polarization separator each having a common port and a pair of polarization ports, means coupling the source to one polarization port of the first separator, means coupling the common port of the first separator and the first horn, means coupling the common port of the second separator and the second horn, and means including a first 90* polarization rotator for coupling one polarization port of the second separator and its other polarization port.

Claim 16

Apparatus as in claim 14 wherein the means coupling the two polarization ports of the second separator includes a delay line.

Claim 17

Apparatus as in claim 14 wherein the means coupling the attenuated energy to the first detector includes the other polarization port of the first separator.

Claim 18

Apparatus as in claim 14 wherein the means coupling the attenuated energy to the first detector includes a second 90* polarization rotator and means coupling the other polarization port of the first separator to the second rotator.

Claim 19

Apparatus as in claim 14 wherein said material comprises a generally planar web and wherein the horns are so oriented that radiation therebetween passes through the web at an appreciable angle from a normal to its plane.

Claim 20

Apparatus as in claim 1 wherein the source operates in the frequency band from 20 GHz to 25 GHz.

Claim 21

Apparatus as in claim 1 wherein the variable frequency source comprises a backward wave oscillator.

Claim 22

Apparatus as in claim 1 wherein said material comprises a web and wherein the radiating means comprises a pair of horn antennas disposed on opposite sides of the web and mounted on a U-shaped member adapted to be moved transversely across the width of the web.

Claim 23

Apparatus as in claim 1 wherein the construction of the lens-corrected horn is such as to provide a parallel beam having a planar wavefront.

Claim 24

Apparatus as in claim 1 wherein the means coupling the attenuated energy to the first detector includes a second lens-corrected horn.

Claim 25

Apparatus as in claim 1 wherein the corrected horn includes a plano-convex converging lens.

Claim 26

Apparatus as in claim 1 wherein the corrected horn includes a double refraction converging lens.

Claim 27

Apparatus as in claim 1 wherein the corrected horn includes a single refraction converging lens.

Claim 28

Apparatus as in claim 1 wherein the corrected horn includes a stepped approximation of a converging lens.

Claim 29

Apparatus as in claim 1 wherein the means coupling the attenuated energy to the first detector includes a second horn, the apparatus further including a band-pass filter and means coupling the detector to the filter, the filter having a pass band sufficiently narrow to reject the fundamental component of modulation caused by mismatch reflections between the two horns.