Quarter-Wavelength Stepped-Impedance Resonator Filter With Mixed Electric and Magnetic Coupling

This letter proposes a new type of microstrip quarter-wavelength stepped-impedance resonator (SIR) filter with controllable mixed electric and magnetic coupling. A conducting pin and an open gap between two coupled SIRs are jointly used to create the mixed coupling, and the electric and magnetic coupling can be separately controlled by adjusting the spacing between the gap and the position of the conducting pin. Based on the proposed structure, a second-order filter and a third-order filter are designed and fabricated. Good agreement between the measured and simulated data is obtained.