Abstract: A device for measuring the relative proportions of gas, oil and water in a conductive pipe includes at least one open-ended, conductive tube having a radius different from the pipe, disposed within the pipe. Microwave transmission structure transmits microwave signals along the pipe and the at least one tube at a plurality of frequencies, the pipe and the at least one conductive tube acting as waveguides for the microwave signals. At least two microwave receiving devices are disposed at separate positions having different respective radii, spaced apart along the pipe and at least one tube, for receiving the microwave signals transmitted by the transmission structure. Determining circuitry determines the relative proportions of gas, water and oil in the pipe by comparing the transmitted and received signals.

Abstract: Waveguide switching apparatus includes a stator and a rotor arranged to rotate relative to it. The rotor includes passages therethrough arranged to make connections between channels in the stator depending on the relative position of the rotor and stator. One passage is defined partly by the rotor and partly by the stator. This reduces the inertia of the rotor compared with a conventional switch in which all passages are entirely contained within the rotor, and thus improves switching accuracy. A passage in the rotor may have a dimension, in a plane transverse to the axis of rotation, which varies along its length, being smallest at its mid-length. Curved passages in the rotor may be arranged such that tangents to their center lines at their ports are non-radial. This enables the diameter of the rotor to be smaller than would otherwise be required. In another aspect of the invention, an asymmetric circumferential slot arrangment is included in the rotor.