Cross-coupled stepped-impedance resonators improved bandpass filter charateristic

Novel Microstrip open loop resonator bandpass filter based on a basic stepped-impedance resonator is proposed in this paper. The optimal design for a miniaturized stepped-impedance resonator is employed by this layout, which can be reduce the filter size and improve the spurious suppression. The structure of the proposed filter consists of a quarter wavelength coupler and stepped-impedance resonator which have the electrical length and characteristic impedance of λ/16 and Z₀ respectively. The filter has not only second and third spurious suppressions due to the slow-wave effect but it also has the high directivity. The measured results are in good agreement with the simulated prediction characteristics and validates the proposed filter prototype and corresponding design theory.