Novel Coupled-Line Microstrip Bandpass Filter with 2nd & 3rd Spurious Passbands Suppression

In this paper, a novel parallel coupled-line filter structure based on a reformulation of the sinusoidal modulation of the wiggly-line filter is proposed. With this new filter, both 2nd and 3rd harmonics spurious passbands can be reduced significantly. In order to demonstrate the proposed filter performance, three prototype filters are designed @ 900MHz with 10% fractional BW. From the simulation and experimental results, more than 25dB suppression in the second harmonic spurious passband has been obtained for the wiggly-line filter and its modified version. But, only the new filter can obtain about 14dB suppression in the third harmonic spurious passband.