Patent GB-712474-A (GB)
Title: Improvements in electron discharge devices combined with waveguides
Inventor: HAWKINS PHILIP OWEN
IPC: H03C7/02
Filed: 1949-11-01
Abstract: 712,474. High-frequency discharge apparatus. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Oct. 31, 1950 [Nov. 1, 1949; March 31, 1950; April 5, 1950], Nos. 27944/49, 8102/50 and 8522/50. Class 39(1) [Also in Groups XXXVI, XL(b) and XL(c)] Two waveguides or parts of the same waveguide are coupled by a discharge tube having inside a glass or ceramic envelope a tubular anode at least #/2 long and a cathode extending along the axis of the anode to form a section of coaxial line. The length of the anode is preferably 3#. The device may function as a diode, Fig. 1; alternatively an extra helix electrode 8, Fig. 2, may be provided which functions as a retardation line and perhaps also as a control grid. In Fig. 2, the cathode and electrode 8 together form the inner conductor of the coaxial line. The cathode has sleeves 4 at either end which co-operate with flanges 5 on guides 6 to form choke joints. Matching plungers 10 are provided. The electromagnetic waves are propagated along the coaxial line in a mode with a radial electric component which decreases radially outwardly so that electrons entering the field in a positive half cycle are accelerated by a strong field and when the field reverses the same electrons are in a region of weaker field so that their velocity is not reduced to zero; those entering the field in a negative half cycle return to the cathode. Consequently the electrons can reach the anode even without an applied D.C. field between the anode and cathode, the transit time for example being 4.3 cycles, Fig. 3, (not shown). The device can be used to rectify pulses flowing along the coaxial line, and hence for the observation of pulses of a radar transmitter and the continuous monitoring of the power output thereof. The anode is charged to a negative potential, by the impinging electrons, which is just sufficient to prevent any more electrons from reaching it and consequently this potential depends on and is directly proportional to the amount of high frequency power flowing through the device. The output voltage from the anode lead is fed to an oscilloscope without the interposition of a wideband amplifier. The device may be gas- or vapourfilled, such as with neon, at a pressure of 0.1-10 mms. instead of being evacuated. In this case a positive potential is applied to the anode so as to ionize the filling and the tube will then absorb energy from the waves and serve as an attenuator. The tube can thus be used to amplitude modulate continuous waves or pulses by modulating the anode voltage, or reflected waves fed out through a third waveguide incorporating a magic T ' junction may be modulated in this way. At low power levels the anode current is proportional to the power flowing through the device so that the device can be used as a wattmeter. The device may be used for harmonic generation by inserting a probe tuned to the required harmonic at the output end of the tube. In this case 80 per cent of the input power is absorbed or reflected to set up standing waves and 40-50 per cent is converted to an anodecathode direct current. The Provisional Specifications suggest in addition that interaction may take place between the waves and a stationary space charge in the tube. The first Provisional Specification states that the grid may be a mesh or formed of rods or strips in which case it is non-waveretarding. The first and second Provisional Specifications specifically refer to the cathode tensioning spring shown in Fig. 2.