Bandstop filter with a wider upper passband using microstrip open-loop resonator

We propose a bandstop filter with a wider upper passband using microstrip open-loop resonators for modem communication systems. A microstrip open-loop resonator (MOLR) is discussed for maximum miniaturization in microwave applications and to obtain a wider upper stopband (or passband) including the first spurious resonance frequency for planar filters. The bandstop filter is designed and fabricated using a full-wave simulator. The measured filter performance shows a good agreement with the simulated response.