Harmonic Suppression Improvement of Microstrip Open Loop Ring Resonator Bandpass Filter

This paper proposes the new design of open loop ring resonators with electric coupling type for bandpass filter and its efficiency enhancement by employing the microstrip line loaded with rectangular ends and improved harmonics suppression using the two open loop ring resonator. The filters are not only spurious suppression due to the slow-wave effect but also have the high directivity. The filter design of this type is described in detail. The experimental results are demonstrated and discussed.