Multi-mode bandstop filter using defected equilateral triangular patch resonator

Microstrip multi-band bandstop filters using tri-mode equilateral triangular patch resonator are developed, and the rules of resonant frequency and patch defection dimension are obtained by calculation. With fractal patch defection and a higher substrate permittivity, higher order modes of resonator are activized for the multi-band implementation, and the dominant mode TM_1,0,-1, and the higher order modes TM_1,1,-2 and TM_2,-2,0 are fully applied, and filter performances are greatly enhanced. The design is demonstrated by experiment. The proposed filters have advantages of simple topology, compact size and nicer performances, and all these features are well popular for wireless communication systems.