The design of a matching circuit for dielectric-filled open-ended waveguide antenna

The design of a matching circuit, consisting of an air gap in the transmission line that feeds a dielectric-filled, open-ended waveguide antenna is discussed. The Mode Matching Method is employed for assembling the Generalized Admittance Matrix of a matching circuit (this matrix yielding, in turn, an equivalent, n lumped elements circuit) and for determining the impedance of the radiating aperture. An ideal matching network that matches the aperture´s impedance to the characteristic impedance of the waveguide is derived hy using the circuit theory. The optimal air gap´s position and length are then retrieved by minimizing the deviation between the values of the elements in the ideal network and those in the equivalent li circuit. Simulation results and measurements are presented for a rectangular aperture operating in the L-hand.