Multi-Suppression of Microstrip Bandpass Filter Using Split-Mode Excitations

Abstract

A novel method for spurious suppression in bandpass filter using Split-Mode Excitations (SME) is proposed. Distinct from traditional ways for spurious suppression, the proposed method uses different excitations for six-order quarter-wavelength resonators to obtain good out-of-band performance. According to the split-mode, the proposed bandpass filter with wideband spurious suppression was designed by using three effective excitations to produce three spurious conditions. In this way, the proposed circuit has a very small size, only amounting to 0.08 by 0.32 guided wavelength at the center frequency of 2.4 GHz. The out-of-band performance is improved easily and effectively with a rejection level better than 20 dB at least up to 20 GHz and done without using any cascaded circuits.