Miniature wideband bandpass filter based on electric and magnetic coupling paths

A compact wideband bandpass filter design that provides a sharp roll-off and low loss performance is presented. The design is based on employing two separate paths between the adjacent resonators constituting the filter, where one path enables electric coupling and the other one magnetic coupling. This structure generates zeros in the filter's transmission response due to the dominance of electric coupling. A fourth-order filter was fabricated and tested. Correlation between the simulated and measured results is remarkable. The measured results confirm the fractional bandwidth of 70% at the centre frequency of 4.58 GHz, insertion-loss is <0.55 dB with a return-loss better than 15 dB in the passband. The filter occupies an area of 4.1 x 17.8 mm, which corresponds to 0.1 lambda(o) x 0.44 lambda(o), where lambda(o) is the wavelength of the centre frequency.