An Automatic Impedance Recorder for X-Band

Abstract

A broadband, low-power, automatic impedance recorder of good accuracy has been developed for the X-band frequency range. The instrument will accept any impedance which has an X-band waveguide input and will plot an ink graph of either the impedance or the admittance upon a standard Smith type impedance chart. If the test impedance is one of low mismatch, the instrument can be switched to an expanded Smith chart scale and thus provide greater plotting accuracy near the matched condition. The plane of impedance measurement, or "reference terminals," of the instrument may be located at any point desired along the waveguide transmission line leading to the test impedance and will remain fixed for all frequencies in the operating band. An rf impedance circuit utilizing broadband waveguide components extracts the amplitude and phase information which operates electromechanical servos in the amplifier-recorder unit. The components presently in use give an operating bandwidth from 8400 mc to 9900 mc, and the arrangement is such that the system will operate on any incident rf power level within the range of about 20 to 250 milliwatts. Everyday laboratory use of the instrument by both professional and nonprofessional personnel has shown it to be accurate, reliable, and a great time saver. . Lab., Washington, D.C., August, 1953.