A harmonic suppression bandpass filter designed by E-type SIR with shunt open stub

This paper propose a bandpass filter structure for improved harmonic suppression in the stopband and let the area become smaller. This filter is designed by the half-wavelength microstrip line, and its operating frequency is at 3.4GHz. The operating frequency properties in the WiMAX band are achieved. The filter is composed of two E-type resonators, which are improved from the open-loop resonator by adding small shunt open stub to perturb 2^nd harmonic. For saving design space, this paper uses the stepped-impedance resonator (SIR) and the multi-layer boards to arrive the purpose. The filter would be tested and verified on the printed circuit board (PCB), and achieve the filter on the laminate process. Finally, we would compare to other open-loop ring resonator.