320 the second resonator 330 the third resonator 340 and the output port 350 are manufactured on a substrate having a dielectric constant of 3 38 and a thickness of 20 mils the general circuit board manufacturing method is used as its manufacturing method in other words photographing chemical manufacturing process including adding photoresist exposure etching have been applied further the grounding of both ends of the second resonator 330 is achieved by using the method of coating metal on the through hole or by using the method of inserting the grounded pole wherein since the central frequency of the selected open short terminated coupled line filter is 5 8 ghz the length of the selected first resonator 320 and the third resonator 340 is 612 mils the length of the second resonator 330 is 636 mils and all the coupling distance between the resonators is 4 mils for adapting to the required central frequency referring to fig4 it schematically shows the frequency response curves measured from the manufactured filter as shown in the diagram the central frequency is 5 8 ghz the pass band is about 5 5 u02dc 6 2 ghz the insertion loss is about 1 5 u02dc 2 db the return loss is greater than 10 db and the image rejection capability in lower stop band point c is around u2212 70 db further at point d the rejection of upper stop band is around u2212 50 db the rejection of filter is much better than the conventional parallel coupled resonator as show in fig2 therefore following advantages of can be achieved 1 by bending the resonator the length of whole filter can be shortened 2 the cross coupling between the first resonator and the third resonator.