Early demonstration of a high VSWR microwave coaxial programmable impedance tuner with coaxial slugs

Abstract

This paper reports a high voltage standing wave ratio (VSWR) impedance tuner with two independent slugs, which slide along a low-loss coaxial line. Impedance tuner are instruments used for characterizing performances of active microwave components and systems, and more particularly for load-pull and source-pull measurement of transistors, power or low noise amplifiers. After presenting the proposed tuner principle, a demonstrator based on a 3.5 mm coaxial line and designed to operate at microwave frequencies from 2 to 18 GHz is introduced. Then, its performances are measured and compared to simulation results. Finally, overall performances are compared to other currently commercialized impedance tuner technologies. Depending on the targeted frequency band, different slugs can be used to obtain an optimal VSWR. Slugs typically offers a 200:1 VSWR. Their dimensions can be optimized in order to achieve very high VSWR in excess of 300:1. The demonstrated tuner is very compact and achieve a minimum repeatability of -40 dB.