Single- and dual-band bandstop filters with fully controllable stopband characteristics

ABSTRACT This paper presents a novel design method of bandstop filters (BSFs) and dual-band bandstop filter (DBBSF) with completely controlled bandwidth and centre frequency, high rejection levels at mid-stopband and compact sizes. First, bandstop units with simple structures are proposed. Through theoretical analysis, the centre frequency and bandwidth of the bandstop units can be independently controlled by tuning the parameters of the loaded stubs. Then, single-band, dual-band bandstop units and compact J-inverters are adopted to design the filters. Finally, to demonstrate the proposed design method, 2-order, 3-order and dual-band BSFs are fabricated and measured. From the experimental results, the maximum rejection levels at mid-stopband of 2- and 3-order are around 50 dB and 70 dB, respectively. The two stopbands of the DBBSF can be fully controlled. The measured maximum rejection levels at the two mid-stopbands are both around 60 dB. Furthermore, all the simulation and measurement show good agreement.

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