An automatic standing wave indicator

Standing wave patterns in an x-band wave guide are reproduced on a cathode ray tube in a new automatic standing wave indicator developed at the Naval Research Laboratory. The essential units of the instrument are a novel motor-driven “reciprocating probe,” conventional high-gain audio amplifier, and a special cathode ray indicator. The reciprocating probe, shown in Figure 1, is basically similar to a conventional slotted line probe, although a motor has been added to make probe travel automatic. As the probe travels automatically back and forth, an associated potentiometer arrangement generates a horizontal sweep voltage for the indicator. The combination of this horizontal sweep and the amplified detector output allows reproduction of the wave guide standing wave pattern on the cathode ray tube. Measurements of standing wave ratio are made directly from the cathode ray picture through a calibrated screen, and indications of relative phase of the pattern are read from a calibrated dial. This type of presentation allows unusually rapid adjustment of radio-frequency components since effects of adjustments are instantly apparent. A number of novel techniques are made possible with the instrument.