GB995839A - Improvements in and relating to devices for controlling electromagnetic waves at microwave frequencies - Google Patents

Abstract

995,839. Semi-conductor devices; electromagnetic waveguides. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. June 8, 1961 [July 20, 1960], No. 25308/60. Headings H1K and H1W. A microwave variable impedance element for controlling flow of microwave energy along a waveguide when mounted transversely therein comprises a semi-conductor wafer capable of passing such energy through its thickness without substantial attenuation provided with an ohmic contact electrode and a PN junction forming electrode. The bias condition determines the transmission properties. As shown in the drawings the electrodes may be strips along opposite wafer edges. Alternatively, they may consist of aligned lattices on opposite faces, or interdigitated combs on one face of the wafer. In a modification of the latter arrangement the PN forming electrode is replaced by a line of discrete dot junctions wired together. In another device sets of parallel strip electrodes ohmic on one wafer face and PN junction forming on the other are interconnected by spaced rods extending through the wafer to provide in effect a series connection of the junctions. Such a connection may alternatively be provided by stacking a series of wafers with edge electrodes edge-to-edge. A typical use of the element is illustrated in Fig. 7, where the element is mounted in the common wall of a pair of rectangular waveguides. When a highpower signal to be transmitted to an aerial is to the conductive condition to form a continuation of the common wall. On the other hand lowenergy signals passing along guide 74 from the aerial switch it to its insulating state to allow the signal to cross into waveguide 75 at the head of which is a receiver.