Microstrip Dual-Band Bandpass Filter Using U-Shaped Resonators

Coupled resonators are widely used in the design of cross-coupled filters with dual-passband response and the quasi-elliptic function characteristics. In this paper, we will present a dual-band bandpass filter using only couplings between adjacent resonators, i.e. without cross-couplings. The dual-band bandpass filter with passband centre frequencies of 1747 MHz and 1880 MHz respectively is designed and fabricated using microstrip U-shaped resonators. Using coupled resonator pair as a dual-band cluster, a miniaturised structure is achieved as compared to the conventional topology. The measured responses agree closely with the simulations.