GB760317A - Improvements in or relating to microwave apparatus - Google Patents

Abstract

760,317. Waveguide accessories. DECCA RECORD CO., Ltd. Dec. 24, 1953 [Dec. 24, 1952], No. 32759/52. Class 40 (8). [Also in Group XL (c)] Dielectric material, such as barium titanate, whose dielectric constant can be controlled by means of an applied potential gradient is used to modify an incident microwave signal, means being provided for extracting from the modified signal a component of different frequency from that of the input signal. The material may be arranged in the form of a thin sheet extending across a waveguide, fired-on silver electrodes in the form of strips running parallel to the broad face of the guide being provided on each side of the sheet. Alternatively, electrodes are provided on one side only of the sheet, alternate strips being connected to a terminal at one edge of the sheet and the remainder being connected to a terminal at the opposite edge. The sheet may be built up of a number of slabs 15, Fig. 3, of dielectric material lying parallel to the broad face 16 of the guide, the interengaging surfaces being made conductive on both sides of the slabs. The slabs are staggered slightly and a small exposed strip is left non-conductive at one end of each face. The exposed conductive portions are connected to common terminals at each side of the guide. In an arrangement suitable for a circular waveguide 32, Fig. 4, the potential gradient is established between a central electrode 38 (via an insulated lead 36) and the walls of the guide. Other methods of applying the control potential are by ionized gas chambers on either side of the dielectric material or by mercury electrodes. In order to match the dielectric slab to the rest of the guide it may be arranged to slope in the direction of propagation within the guide. Alternatively a wedge or inverse wedge 52 of a material having a dielectric constant intermediate between that of the element 48 and that of the rest of the guide may be arranged in front of the element. Intermediate elements 49, 50, 51 of higher dielectric constant may be arranged between the element 48 and the matching means 52. Such elements may be made by mixing powdered titanates with polyfoam. Since the change in dielectric constant of the titanate or like dielectric material is independent of the direction of the electric field an element of the material placed in a waveguide will produce equal distortion of opposite half-cycles of the incident microwave field. If, however, a biasing voltage is applied to the element the distortion of opposite half-cycles will be different and the arrangement may be used as a detector or mixer. Alternatively, the harmonies (particularly the second harmonic) present in the distorted output may be selectively extracted from the output signal. For this purpose a waveguide dimensioned below cut-off for the unwanted frequencies may be used. Specifications 760,386, 760,387, 760,388, [Group XL (c)], and 760,389 are referred to.