An Improved Method for Accurate Extraction of Coupling Coefficient Between a Lossy Radiator and a Lossless Resonator in Filtering Antennas

A unique method for accurate extraction of coupling coefficient between a lossy radiator and a lossless resonator is proposed in this paper to facilitate the synthesis design of filtering antennas. To remove the parasitic effect of the radiation loss in extraction of coupling coefficient, the network parameters of the coupled resonators in lossless condition is derived and regained from the original lossy network. The unique relationship between the ABCD matrices of the lossless and lossy networks is revealed in detail via their closed-form expressions for both parallel- and series-resonant cases. Next, the coupling coefficient between a rectangular patch antenna and a λ/2 resonator is numerically extracted with the proposed method, which is further utilized to design a filtering antenna. Finally, the filtering antenna prototype is fabricated and measured, and good agreement among the theoretical, simulated, and measured results has experimentally verified the validity of the proposed method.