A compact wide-band bandpass filter using the microstrip loop resonators with connected four inner corner identical branches and outer tuning stubs

This paper proposes a compact wide-band bandpass filter using the properties of microstrip open-loop resonators with outer tuning stubs. The microstrip loop resonator consists of four identical branches and each branch is a open-loop microstrip element. An introduced bandpass filter is based on the bandstop filter employing the direct-connected feed lines on the orthogonal of the microstrip loop resonators. The introduction of two outer tuning stubs connecting opposite to the ports widens the passband and sharpens the stopbands. The filter is designed at center frequency of 2.45 GHz and simulated by IE3D. The measurement of fabricated structure proposes 37% bandwidth and 0.84 dB insertion loss.