COMPACT SUB-WAVELENGTH MICROSTRIP BAND-REJECT FILTER BASED ON INTER-DIGITAL CAPACITANCE LOADED LOOP RESONATORS

摘要

In this article, the microstrip band-reject filters based on inter-digital capacitance loaded loop resonators (IDCLLRs) are proposed by using meandered microstip-line, which enhances the coupling to the resonators and provides more structural parameters for flexible design. First, an IDCLLR-based single-stage meandered prototype of band-reject filter has been designed and fabricated. The measured frequency response shows 2.2% relative stop-bandwidth (-10 dB) with -21 dB maximal insertion-loss at 3.34 GHz. Furthermore, the resonant frequencies versus inter-digital length are studied. Finally, an IDCLLR-based three-stage meandered prototype of band-reject filter was designed and fabricated too, the measured relative stop-bandwidth (-10 dB) is 6.2% and the insertion-loss at center frequency approaches -42 dB.