In this letter, the operating mechanism of proposed bandstop filters with asymmetric multiple-mode resonator loaded with tree-shape branches is introduced. Based on the design procedure, centre frequencies of the proposed bandstop filters can be controlled due to the designed degree of freedom. Meanwhile, the proposed BSFs feature compact sizes and sharp roll-off skirts for transition bands. To validate the design and analysis, a prototype filter has been fabricated with six stopbands centered at 1.91/2.38/3.54/5.19/ 5.79/6.85 GHz. The measured results of the fabricated filter agrees well with the simulation, which shows that the proposed structure is a good candidate for multi-band BSF designs and validates the proposed design flow well.

In this letter, a novel sext-band bandpass filter (BPF) using two split-type multiple-mode resonators is proposed. The filter is composed of two sets of resonators which are respectively designed to realize Filter 1 with two passbands and Filter 2 with quad passbands. Then the two BPFs are combined by parallel coupling feed lines for sext-band responses, and each of the six centre frequencies in the proposed sext-band BPF is able to be controlled due to the design freedom. To validate the design and analysis, a prototype filter has been fabricated with six passbands centered at 1.88/2.59/3.48/5.26/5.82/6.75 GHz. The measured result of the fabricated filter agrees well with the simulation, which shows that the proposed structure is a good candidate for sext-band BPF designs and validates the proposed design flow well.