A three-stub waveguide impedance matching algorithm based on equivalent circuit analysis

Three-stub waveguide is a common impedance matching device, which is widely used in microwave impedance matching system. In this paper, an impedance matching algorithm for three-stub waveguide with large stubs is proposed based on the equivalent circuit analysis method, which can be used to realize continuous real-time impedance matching. First, the equivalent circuit of a single stub is established by using series and parallel reactance, and the equivalent circuit of three-stub waveguide is further established by cascading three single-stub models. Then, the two-port scattering parameters of three-stub waveguide, the load impedance and the impedance of three-stub waveguide are derived. In the matching process, by using the currently detected reflection coefficient and two-port scattering parameters, the terminal load impedance is calculated, and the optimal insertion depths of the stubs are finally determined by using the impedance of three-stub waveguide with different stub depths. This algorithm can reduce the voltage standing wave ratio, and can be easily redesigned for other waveguides.