Dual-band bandpass filter based on mixed electric and magnetic coupling of the hybrid quasi-lumped resonator

A novel compact dual-band bandpass filter based on mixed coupling of the hybrid quasi-lumped resonator is proposed. The filter is composed of two independent signal paths, each can generate one passband with two identical hybrid quasi-lumped resonators. The proposal combines the mixed electric and magnetic coupling technology with this novel resonator in the filter design. Analysis of the filter has been done with the equivalent circuit method. To validate the approach, a dual-band bandpass filter operating at 2.4/5.2GHz has been fabricated. Both passbands were realised with mixed coupling. An additional transmission zero is generated at either passband. Final fabricated filter has good band skirt, low insertion loss and good out-of-band performance. Reasonable agreement is found between the calculated, simulated and measured results. The implementation area is 0.21 lambda(g) x 0.12 lambda(g).