GB1082791A - Transmission line power attenuators - Google Patents

Abstract

1,082,791. Variable attenuators. JOSEPH LUCAS (INDUSTRIES) Ltd. July 2, 1964 [April 3, 1963], No. 13148/63. Heading H1W. [Also in Division G3] A power attenuator for a transmission line such as a waveguide 27 comprises a variableimpedance semi-conductor diode 18 which absorbs or reflects a proportion of the power flowing in the line and which is connected in a bridge network determining the bias applied to, and hence the impedance of, the diode 18. As shown, the four arms of the bridge network include the diode 18, resistors 15, 16 and a variable resistor 19. The input to the bridge is derived from an oscillator 5 by way of one secondary winding 8 of a transformer 7; the output from the bridge is applied over an amplifier 23 to a phase-sensitive detector 24 having another input from secondary winding 9 of transformer 7. The output from detector 24 is applied over a variable D.C. source 25 and inductor 26 to bias the diode 18. The arrangement is such that for any given setting of source 25 and resistor 19 the detector 24 produces an output which biases diode 18 to change its impedance until an equilibrium condition is reached; the bias across the diode will then automatically vary to maintain the diode impedance substantially constant despite, for example, temperature changes. The diode 18 could be replaced by a varactor diode, a capacitance-sensitive bridge then being necessary. For a magic-tee waveguide two diodes with their associated circuits could be connected in opposite arms, and positioned so that attenuation is high when the impedance of the diodes are balanced and low when the impedances are unbalanced; alternatively the diodes can be positioned so that the power loss from the input waveguide to the output waveguide is at a minimum when the diode impedances are unbalanced.