30 through the circuit board 10 and the fourth coupling section 42 of the second resonator 40 is coupled with the output end 22 through the circuit board 10 as seen from the top view the input end 21 and the first coupling section 31 the output end 22 and the fourth coupling section 42 alike can be fully overlapped to reduce insertion loss besides the example set forth above where the connecting section 33 of the first resonator 30 is collinear with the coupling sections 31 and 32 a design of u shaped resonator may also be formed as shown in a second embodiment in fig4 a 4b and 4 c namely the connecting section 33 is bent and located on one side of the coupling sections 31 and 32 the first resonator 30 and the second resonator 40 are coupled together in the same orientation referring to fig4 a or in the opposite orientation as shown in fig4 b furthermore the coupling sections 31 and 32 can be also located respectively on opposite sides of the connecting section as shown in fig4 c refer to fig5 a and 5b for a third embodiment of the invention the first coupling section 31 of the first resonator 30 is located on a first.