A wide-stopband microstrip bandpass filter using mixed electric and magnetic coupled resonators

This paper introduces a novel wide stopband microstrip bandpass filter working at 2 GHz. Stepped-impedance quarter-wavelength resonators are used here to reduce the size of the filter. Mixed electric and magnetic coupling between the resonators are adopted to introduce two transmission zeros on each side of the passband. Thus, the selectivity of the filter is improved. Also, due to the cancellation of the electric coupling and the magnetic coupling, the first spurious passband is suppressed and the stopband rejection is more than 20 dB up to 10 GHz. The measured results show that the filter is working at a center frequency of 1.95 GHz, with a fractional bandwidth of 5%. Simulated and measured results agree with each other very well.