Patent GB-835905-A (GB)
IPC: H01J17/04
Abstract: 835,905. Waveguide switches. COMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. Nov. 13, 1956 [Dec. 29, 1955], No. 34697/56. Class 40 (8). [Also in Group XXXVI] A waveguide switch comprises a plate of semiconducting material positioned across a waveguide and means for making the plate either transparent or opaque to electromagnetic wave energy. The plate has one face polished and the other ground or frosted and is subject to electric and magnetic fields directed perpendicular to each other in the plane of the plate. The relative directions of the fields determine the direction of movement of holes and electrons towards one or other of the faces, and since the faces have different recombination velocities, reversal of one of the fields causes a change in carrier concentration within the semi-conductor. Thus for one direction of either the electric or magnetic field the plate becomes a conductor and for the other, an insulator. The plate 12, Fig. 1, consisting of e.g. germanium or silicon, may be situated at the junction of a stub waveguide 7 connected at one end to a receiver 9 and at the other to the waveguide transmission channel 1 between a transmitter 3 and an antenna 2. The magnetic field H may be provided by the magnet of the transmitter magnetron, whilst the electric field is provided by a potential applied to electrodes on the edges of the plate, these electrodes being connected to the timing device 4 of the transmitter 3. Under normal conditions the fields are such that the plate is non-conductive, e.g. transparent. Upon emission of a signal, the trigger pulses of the timer 4 are sufficient to reverse the electric field within the plate and render it conductive so that the transmitted pulses are prevented from affecting the receiver 9. During the times that echo pulses are received, the plate is transparent and the pulses propagate towards the receiver 9. The receiver is matched to the antenna by means of aquarter-wavelength matching stub 8 provided with a plate 11 similar to plate 12 and situated one quarter wavelength from the stub 7. In the modification of Fig. 9, two waveguides 25, 26 are interconnected by a pair of 3 db. couplers 28, 29 between which are situated a pair of semi-conductor plates 30, 31 (one in either guide) similar to the plate 12. During transmission the plates are conductive and the whole of the energy from the transmitter 3 reaches the antenna 2. When an echo is received the plates are transparent and the whole of the echo pulse is transmitted to the receiver 9. In a modification of this arrangement (Fig. 10, not shown) the two 3 db. couplers are replaced by a single total-coupling junction across which the semi-conductor plate of the invention is arranged. In the various circuits the semiconductor plate may be the same size as, or larger, or smaller than the waveguide it is placed across. It may be arranged in a frame to form a resonant window (Fig. 5, not shown) or several plates 17a, 17b, 17c, Fig. 6, may be arranged side by side in a frame 24. Several contiguous plates may be arranged in a single aperture in a frame of insulating material (Fig. 7, not shown). The switch of Fig. 8 comprises three plates 17d, 17e, 17f spaced at intervals of a quarter-wavelength in the stub 7. Specification 750,134 is referred to. Reference has been directed by the Comptroller to Specification 800,029.