Open loop resonator bandpass filters design using the parallel coupled line technique

This paper describes the design of open loop ring resonator based on the parallel coupled line technique, enhances efficiency by using the quadruply-step impedance transmission line. The proposed resonator is consisted of three sections quarter wavelength coupler and each of sections has the folded open-stubs with the electrical length and characteristic impedance λ/8 and Z
₀
connected in the end of each ports. The spurious response at 2f
₀
and 3f
₀
are appeared. The directivity enhanced parallel-coupler should be employed to solve this problem. The experimental results and designs of all type are 0.9 GHz to implement bandpass filters. There were evidently shown the second spurious response suppression improvement and shifted third spurious response to higher frequency. Both the theoretical and experimental performance is presented.