In this paper, a novel spurious response suppression hairpin bandpass filter is proposed based on the reformulation of the sinusoidal modulation of the wiggly coupled-line. Equal phase velocity can be achieved by the asymmetrical strip width modulation, resulting in significant spurious bandpass suppression. In order to demonstrate the proposed filter performance, two prototype filters are designed @900MHz with 10% fractional bandwidth. From the simulation and experimental results, more than 15dB suppression in the 2nd harmonic spurious passband has been obtained.