Abstract: This method of constructing microwave systems and processing the signal by correlation is applicable notably to tachometric, telemetric, directional and tracking control systems, to the detection of heterogeneousness and discontinuity in materials by using sensors of the direct-contact or contactless type.

Abstract: The temperature of a planar material (8) moving down a process path is measured by causing the material to pass through two openings (3,4) made in a waveguide (1) in such a way that the material effectively does not cut the electric field lines present on the walls of the guide (1) and also so the material (8) passes through the guide in a direction generally parallel to the electric field in the propagation mode of the waveguide and through a region of maximum field strength. The temperature of the planar material (8) is determined by measuring the thermal noise emitted by the material (8) as it passes through the slotted waveguide (1). The slots (3,4) for a rectangular waveguide operating in the TE.sub.10 mode are made along the centerline of the two broad sides of the guide.

Abstract: To measure the temperature of a sub-surface volume of a body, for example, living tissue, in microwaves, at least two probes are placed on or near the surface of the body to pick up thermal noise in the microwave range. The two probes are positioned so that the volumes of the body from which the respective probes receive thermal noise signals overlap to provide a common volume from which both of the probes receive thermal noise signals. The signals received by the probes are processed so as to be amplified and to accentuate the signals emitted by the common volume relative to the signals omitted by the remainder of the volumes from which the probes receive thermal noise signals. In one form of apparatus, the two probes are connected in parallel to a correlator the output of which is connected to an amplifier-receiver. In another form of apparatus the probes are connected to an amplifier-receiver, one being connected through a phase shifter.