Tuning element of high power 2.45-GHz coaxial impedance transformer

The paper presents theoretical analysis, equivalent circuit and electromagnetic modeling of one element of a three-stub coaxial impedance transformer (tuner) planned for high-power impedance matching in 2.45 GHz ISM band. The element consists of the main coaxial transmission line (EIA 1 5/8") traversing a waveguide section terminated at one end by a fixed short and at the other end by a sliding short. The coaxial line enters the guide broad wall perpendicularly, close to the fixed short. It can be proved that when moving the sliding short, the locus of S₁₁ is a circle that necessarily passes the origin and touches the unit circle, which is a prerequisite for using such a structure as a tuning element in three-stub tuners.