Patent GB-851881-A (GB)
Title: Improvements relating to duplexer devices
IPC: H01J17/04
Filed: 1958-03-25
Abstract: 851,881. Waveguide switches; filters. COMPAGNIE FRANCAISE THOMSON-HOUSTON. March 25, 1958 [March 26, 1957], No. 9593/58. Class 40(8). [Also in Group XL(a)] A duplexer device comprises an evacuated envelope defining a resonant structure containing a pair of spaced apart electrodes having a coefficient of secondary electron emission greater than unity and input coupling means for applying high frequency wave energy between said electrodes, the arrangement being such that for incident energy of an appropriate frequency within the band depending on the distance apart between the electrodes an electronic discharge will be produced by incident energy of above a particular magnitude, which discharge acts to substantially short circuit the input coupling means. The device may be used as a TR, pre-TR or TB switch, and changes between a high and a low impedance condition in an extremely short time as compared with prior gas-filled devices. In one arrangement, Fig. 4, two electrodes 20 and 23 are mounted in a cavity resonator. Electrode 20 is mounted on a flexible membrane 21 and can be moved by a screw 22. Electrode 23 contains an auxiliary filamentary cathode 24 supported by lead wires 25 and 26 which are connected to a heating source 30, one pole of which is connected to the casing. A cylindrical element 27 mounted on a flexible membrane 28 is adjustable by a screw 29 to provide capacitive tuning of the resonator. A glass coupling window 30<SP>1</SP> is provided in one wall of the resonator when the device is used as a TB switch. If the device is used as a TR switch, an additional window is provided in the opposite wall of the resonator. An Alternative arrangement, Fig. 5 (not shown), suitable for use as a TR or pre-TR switch, comprises a length of rectangular waveguide sealed by a window at each end and containing three resonant elements spaced at quarter wave intervals, each element consisting of two fixed conical electrodes. One electrode encloses an auxiliary cathode as shown in Fig. 4. Figs. 7a and 7b show a device comprising an H-shaped guide 41, half a wavelength long, coupled through sealing windows 42 and 49 to rectangular guides 43 and 45. A radioactive source 46 provides electrons to initiate the discharge and ensures that the discharge becomes stabilized at the input end of the guide in preference to the output end. The guide 41 has flanges 47 and 47<SP>1</SP> which are seated in fittings 48 and 48<SP>1</SP> integral with the guides 43 and 45 to enable the guide 41 to be rotated for matching purposes and to enable the impedance of the device to be varied so that it may be operated as a TR switch or as a pre-TR switch. A TB switch, Figs, 6a and 6b (not shown) comprises a quarter wave length of similar H-shaped guide with a sealing window at one end, and may be provided with a similar rotatable coupling. Fig. 8a shows a device for use as a TR or pre-TR switch comprising sections of H-shaped guide forming filter elements. Sections 49, 51 and 53 have a low characteristic impedance and are approximately a half wavelength long. Sections 50 and 52 have a higher characteristic impedance and are approximately a quarter wavelength long. A radioactive element 56 is provided in a cavity 57 in section 49 and the device is sealed by glass or mica windows 54 and 55. Rotatable couplings may be provided at the ends of the device.