Abstract:Based on odd-even mode theory and multidirectional-feed coupling, a cross-shaped new structure Tri-band Band-Pass Filter(TBPF) with folded stub is studied and designed on the basis of cross-shaped Dual-band Band-Pass Filter(DBPF). The structure analysis shows that the TBPF based on multidirectional-feed has the characteristics of flexible and independent adjustment at the three center frequencies, easy cascade structure, miniaturization and less frequency design parameters. The simulation results show that the added feed-direction excites the third passband of the filter. The designed TBPF has good performance in 5G medium-low frequency band and Indoor WiFi band. Literature comparison shows that the proposed multi-directional feed design method reduces the structure complexity and the number of frequency design parameters of the resonator. Meantime, this method can provide reference for increasing passband numbers of the basic resonator.