A dual-mode wide-band bandpass filter using the microstrip loop resonator with tuning stubs

This paper proposes a dual-mode wide-band bandpass filter using the microstrip loop resonators with tuning stubs. The filter is based on microstrip loop resonator consists of four identical branches and each branch is a microstrip open-loop element. The introduction of two outer tuning stubs connecting opposite to the ports widens the passband and sharpens the stopbands. The microstip loop resonator have a wide stopband resulting from the dispersion effect and the slow-wave effect. The filter is designed at center frequency of 2.35 GHz and simulated by IE3D. The measurement of fabricated structure proposes 36% bandwidth and 0.28 dB insertion loss.