A wide-band method to measure the equivalent reflection coefficient of signal sources

This paper presents a method to measure the (equivalent) reflection coefficient of signal sources. To make highly-mismatched power detectors, are used stepped impedance lines whose scattering parameters can be accurately obtained from dimensional measurements of their structures such as the radii of the inner and outer conductors and their lengths. Since there is no need to use a Tee or splitter to make a mismatched power detector, the proposed method is more sensitive and therefore more accurate in terms of power measurements than the other methods. Also we can make use of a stepped impedance line available from a verification kit used for VNA verifications by adding inner conductors having different geometries to cover a relatively wide frequency range.

I. Introduction

Accurate measurement of the reflection coefficient of signal source, source itself or together with a three-port device used for a monitoring or leveling, is important for itself and for the accurate measurement of the power to be delivered to a matched detector. Also since the power ratio method is one of the basic techniques for the calibration of power sensors, calibration factor or effective efficiency, accurate measurement of the reflection coefficient of signal source is a key for accurate mismatch factor correction in the power ratio method to get a low uncertainty in power sensor calibrations. So far various methods have been developed for the measurement of the effective reflection coefficient of signal source [1]~[6]. Conventionally a sliding short or a short with an air line has been used with a directional coupler or equivalent. Also a mismatched power meter with phase-shifting two-ports has been used for the reflection coefficient measurement of RF sources.