GB621223A - Improvements in or relating to ultra-short wave receivers - Google Patents

Abstract

621,223. Radio receiving systems; valve circuits; detectors. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Aug. 19, 1946. No. 24713. Convention date, Aug. 20, 1945. [Class 40 (v)] In a micro-wave receiver a pair of micro-wave crystal or thermionic discharge tube detectors are coupled to a wave-guide structure of coaxial line section, or a pair of cavity resonators, in such a manner that the detectors are correctly phased and matched and proper balance obtained. A pair of input signal co-axial lines 1, 3 (Fig. 1), have their inner conductors 5, 7 terminated in a capacitive plate 9 and a coupling loop 11, respectively, within the centre portion of an enclosed wave-guide 13. The plate 9 excites similarly-phased electric fields and the coupling loop 11 excites oppositely phased fields in the ends of the wave-guide 13. Adjacent each end of the wave-guide are coupled two detectors 15, 31, matched to the surge impedance of the waveguide 13 by tuning screws 17, 19 and 39, 41 respectively. Detected signals from the detector 15 and 31 are coupled to an external circuit 20 by a conductor which is byepassed for radio frequency by two capacitive couplings 21 and 57 respectively to the wall of the wave-guide. If the input A is attached to a receiving antenna, and input B to a local oscillator, then by reason of the opposing polarities of the two detectors with respect to the output transformer, there is no output corresponding to amplitude modulation of either signal, whereas due to the reversed R.F. phase at one detector with respect to the other the heterodyne output component . of one detector is reversed and the two detected signals add, producing a pure beat signal. In a modification, Fig. 2 (not shown), a coaxial line may be used instead of the wave-guide 13. Matching adjustments are made on one detector at a time, the other being replaced by a load connected across the wave-guide at l, or m, m. If a pair of cavity resonators is employed instead of the waveguide 13, Fig. 3 (not shown), the two input lines are then terminated by a T-junction comprising in one case oppositely phased coupling loops and in the other similarly phased loops. The T-junction may also incorporate a loss introducing dielectric, Fig. 4 (not shown).