Multi-Bandpass Filters Using Multi-Armed Open Loop Resonators with Direct Feed

A novel type of multi-bandpass filters is proposed. The idea of the proposed filters is to engineer the transmission band using multi-reject band resonators, which are implemented using multi-armed open loop resonators that are directly coupled to the input/output ports. Each resonator pair of arms creates a reject band in the transmission response. By properly adjusting the multi-reject bands, appropriate multi transmission bands are created. The idea was verified by designing three different filters with multi-bandpass response. The designed and fabricated filters have compact size with good agreement between the measured and simulated responses.