The purpose is to produce a non-reciprocal microwave gate circuit having magnetically tunable and frequency-selective properties and branching (decision) functions. Such a gate circuit consists of a cavity resonator (HR) in which a magnetised ferrite element (FE) is arranged. Along the outside of the wall (W) of the cavity resonator (HR) at least one waveguide (HL1) is led via a section and coupled on this section with the cavity resonator (HR) at at least one place. In this case, the coupling position is localised and the waveguide (HL1) has cross-sectional dimensions such that fields spreading out through the waveguide at the coupling position relative to the cavity-resonator middle have at least approximately the same angular velocity as fields rotating in the cavity resonator (HR) (Figure 1). <IMAGE>
