Patent GB-624421-A (GB)
Title: Improvements in and relating to ultra high frequency coupling systems
IPC: H01P1/213
Filed: 1946-01-23
Abstract: 624,421. Discharge apparatus. BRITISH THOMSON-HOUSTON CO., Ltd. (General Electric Co.). Jan. 23, 1946, No. 2241. [Class 39 (i)] [Also in Groups XL (b) and XL (c)] A combined transmitting and receiving system comprises a transmitter connected by a waveguide to a radiator, and a receiver connected to the waveguide by a coupling element which contains a number of walls arranged perpendicular to its length and spaced apart by an odd number of quarter wavelengths, each wall having an aperture tuned to the operating frequency and situated in a gas-filled enclosure, so that waves from the transmitter do not pass directly to the receiver. Fig. 8 shows a radar equipment in which a common radiating and receiving horn 21 is connected by guide 20 to a transmitter 19, and through guide 27 to a receiver 22. Guide 27 includes conducting walls 23-26 spaced a quarter-wavelength apart, wall 23 being one half-wavelength from the junction with guide 20. Each of the walls 23-26 includes a resonant slot 6 surrounded by a seal of borosilicate glass on a cylinder 28 of an iron-nickel-cobalt alloy. The seals 29 are filled with gas and the resonant slots in walls 25, 26 are provided with pulsing electrodes 31 bent inwardly towards the centre of the slots. This arrangement provides a wide band reflectionless coupling for signals of low intensity received by horn 21 and passed by guide 27 to receiver 22. High intensity energy from the transmitter 19 causes the slots in walls 23, 24 to break down and cause considerable attenuation of the waves. As the attenuated wave is not of sufficient intensity to break down the slots in walls 25, 26, pulses are applied to electrodes 31 slightly in advance of the outgoing transmitter pulses to break down the slots in walls 25, 26, and thus give complete attenuation of the waves so as to protect the receiver 22. The pressure and kind of gas in each of the seals 29 may be selected individually. In a modification, Fig. 10 (not shown), instead of an individual gasfilled seal for each resonant slot, the length of guide containing the slots is enclosed by a pair of reflectionless windows of the kind described in Specification 587,812. Graphs are provided to illustrate the band-pass characteristic of the arrangement, and to show the improved attenuation that results from using pulsing electrodes on all the slots, and using a high pulsing voltage. It is also shown that hydrogen is a better filling than argon or nitrogen, and that the recovery time after pulsing is not affected by the addition of small amounts of water vapour. Fig. 23 shows a modification in which the first resonant gap member 77 is separately sealed to give breakdown at one intensity, and elements 72, 73, 74 are collectively sealed at a different gas pressure. Electrodes 78, 79 are connected to a battery, (not shown), to maintain a continuous discharge so as to cause de-coupling from receiver 22 for low values of incident energy. Fig. 26 shows an alternative form of filter in which the resonant frequency of'a cavity between walls 97, 100, having non-resonant apertures 98, 101, is varied by varying the potential applied to the electrodes of a gas discharge tube 103. A suitable form for the resonant apertures for use in any of the embodiments comprises circular openings separated by points, the dimensions being chosen to be resonant at a desired frequency and to break down at a desired energy level. Alternatively, the resonant slots may be rectangular as described in Specification 582,328.