GB597216A - Improvements in or relating to ultra high frequency apparatus employing wave guides - Google Patents

Abstract

597,216. Wave-guides electric resonators. ALLEN, W. D. April 20, 1944, No. 7368. [Classes 40 (iii) and 40 (v)] The flow of energy along a wave-guide is controlled by a resonant conducting ring arranged inside the guide. The ring may act as a filter, an adjustable matching device or as a switching device. Fig. 5 shows a resonant ring arranged in a circular wave-guide, At the resonant frequency, this acts as a series resonant circuit shunted across the guide and gives complete reflection of H 1 waves. For rectangular guides, a rectangular ring with rounded corners is used. The circumference of the ring is somewhat greater than the wavelength in air, and depends on the thickness of the ring and the diameter of the guide. A diaphragm having an annular gap in place of the metal ring acts as a parallel resonant circuit shunted across the guide. The rings may be used as filters and are described as used for this purpose in the E0 to H1 transformers shown in Specifications 597,217 and 597,240 (Figs. 7 and 8, not shown). A ring which is somewhat smaller than the resonant size can be made to resonate when turned about an axis which is normal to the E vector and the axis of the guide. If either a full-sized ring or a smaller ring is rotatably mounted in a guide it can be used as a variable reactance. When parallel to the axis of the guide it presents negligible susceptance. Rotatable rings can thus replace adjustable pistons. Fig. 10 shows a pair of rotatable rings 4, 5 mounted in matching stubs 8, 9 to replace pistons. The rings are rotated until matching is effected. Fig. 13 shows a coaxial feeder 1, 1<1> supplying energy to waveguide 2 or 3 according as ring 4 or 5 is parallel to or normal to the axis of the guide. The rings are simultaneously rotated through 90 degrees by turning the common spindle. A similar arrangement is described for deflecting energy through one or other arm of a Y-shaped guide by means of a single rotatable ring arranged at the junction of the arms (Fig. 14, not shown). The rings may be embedded in polythene to reduce the likelihood of sparking. This slightly modifies its properties. Specification 597,212 also is referred to.