A narrow bandpass filter with wide stopband using short-ended resonator and open-loop resonator with microstrip/slot broadside-coupled unit

A new and miniaturized narrow bandpass filter (BPF) with very wide upper stopband is proposed. The filter consists of an open-loop resonator with the broadside coupled microstrip/slot hybrid unit and a microstrip open-loop resonator with short-circuited units, and the two resonators are edge-coupled to improve the performance of the filter. The effective area of designed filter is about 40.4×20 mm², which shows the compact configuration for the narrow-band filter. The proposed filter has been designed, simulated, and optimized for the wireless communication system. The simulated frequency responses have demonstrated a good narrow-band property from 1.20 GHz to 1.28 GHz (-3 dB bandwidth), which is fractional bandwidth (FBW) of 6.5% at the center frequency 1.24 GHz. Additionally, the filter has also exhibited a wide stopband property up to 13 GHz. Thus, a high selectivity of the proposed filter has been achieved.