GB742948A - Improvements in or relating to apparatus for measuring the magnitude and position ofa standing wave in a waveguide section - Google Patents

Abstract

742,948. Voltage, current, and frequency measurements. ELLIOTT BROS. (LONDON), Ltd. April 26, 1954 [April 29, 1953], No. 11889/53. Class 37. [Also in Group XL (b)] Apparatus for measuring the magnitude and position of a standing wave in a wave-guide section comprises a fourarmed directional coupler junction having a totally reflecting tuning plunger in one of the two arms coupled to the input arm and an unknown impedance coupled to the other of such arms, with a detector coupled by a matching transformer to the decoupled or nominally decoupled arm of the junction; such matching transformer being adjusted to produce no variation of the detector signal as the totally reflecting plunger is moved in or out of its arm with the unknown impedance replaced by a perfectly matching load. Fig. 1 shows a directional coupler of the magic T-type comprising a 4-armed wave-guide junction such that power fed into arm 3 divides itself between arms 4, 6, and arm 7'is normally decoupled from the input; a totally reflecting plunger 5 being inserted in arm 4 and the output arm 6 being connected to an unknown impedance load (not shown). The decoupled arm 7 is connected to the input arm 7a of a matching transformer 2 constituted by a similar magic T-junction whose opposed arms 9, 10 contain reflecting plungers 11, 12 and whose arm 8 is coupled to a crystal detector and indicator (not shown). In operation, output arm 6 is coupled to a matched impedance load and plungers 11, 12 are adjusted until the crystal current is invariable for movement of plunger 5. The matched load is then replaced by the unknown impedance load, and standing wave amplitudes and positions are determined by reciprocating plunger 5 to positions of maximum indicated crystal current. Attenuating vanes may be inserted in the detector arm 8 and input arm 3 to reduce the effect of source or detector impedance variations upon the adjustment of plungers 11, 12, and formulµ are given for the measurement errors to be expected. The input arm 3 and detector arm 8 may be coupled to the narrow faces and arms 7, 7a to the broad faces of arms 4, 6 and 9, 10 respectively (Fig. 2, not shown). The directional coupler and 'matching transformer magic T-junctions may be interconnected over arms 7, 7a of virtual but zero length with arms 4, 6 and 9, 10 mutually perpendicular and arms 3, 8 mutually collinear (Fig. 3, not shown).