GB1114762A - Improvements relating to microwave devices - Google Patents

Abstract

1,114,762. Waveguide switches; semiconductor devices. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. 17 May, 1965 [17 Feb., 1964], No. 6494/64. Headings H1K and H1W. A device for controlling transmission through a waveguide or microwave transmission line comprises an element of semi-conducting material exhibiting relatively high resistivity and having surface layers of low conductivity and of mutually opposite type. As shown, the device comprises a stack of such elements 8. Each may consist of a wafer 1 of n type silicon having a resistivity between 50 and 5,000 # cm. Each wafer carries on one face a layer 2 of p type silicon having a resistivity of 0.01 # cm. and on the other a layer 2a of n type silicon of similar low resistivity. The outer layers are electroded with e.g. nickel layers 4a, 4b and the elements are stacked in two series combinations within iris structures 9 of rectangular waveguide 6. Electrical bias is applied across the waveguide walls and an electrode 10 arranged between the two series of elements. A bias of + 1V. causes injection of carriers into the wafers and the device becomes conductive. Microwave energy does not, however, penetrate, beyond a thin surface layer of the device and the bulk of it serves as a thermally conductive path to the waveguide walls. A bias of between -50 and -2600V is sufficient to produce a depletion layer in the device which thereupon becomes non- conductive. In an alternative application, the elements are annular in form and form a stack which fills a quarter-wave cavity arranged in the outer conductor of a co-axial line. In another arrangement, a stack of cylindrical elements is arranged in a circular waveguide or between the conductors of a co-axial line.