A controllable and low loss dual-band bandpass filter by using a simple ring resonator

A novel structure, which is built by using a simple ring resonator loading open stubs, is adopted to design a dual-band bandpass filter with low loss and controllable characteristics. The fractional bandwidths of two passbands and transmission zeros are controlled by adjusting the length of the loaded open stub and the distance of two feeders. Based on Substrate Integrated Suspended Line (SISL) platform, the filter is designed and implemented with self-packaging and low losses, which are only 0.45/0.83dB of two passbands. The measured results are well agreed with the simulated results.