Compact microstrip cross-coupled bandpass filters using miniaturized stepped impedance resonators

Novel compact microstrip cross-coupled bandpass filters realized by miniaturized stepped impedance resonators (SIR's) are proposed. The cross coupling between non-adjacent resonators is introduced to exhibit a single pair of transmission zeros near the passband at finite frequencies and thus much better selectivity. The optimal design for miniaturized stepped impedance resonator is employed and realized by several layouts in order to reduce the filter size. Two design examples of four-pole cross-coupled filters are described in this paper. The measured results are in good agreement with the simulated predictions. Each proposed cross-coupled filter not only has a compact size but also has high-selectivity and a very wide stopband response.