Second and third harmonic suppression in parallel coupled line filter using sliding coupling

A novel method is presented for 2 nd and 3 rd harmonic suppression in parallel coupled-line band pass filters. It is based on sliding coupling to improved band-reject characteristics of the filters. Easy design, simple implementation, no change in original filter pass-band and good suppression for second and third harmonics are the most advantage of this method. To validate the proposed method, three sample filters are designed and implemented at 3GHz with about 23% band width. The first has -35dB rejection in second harmonic. The second filter has -35dB and -18dB rejection in second and third harmonic consequently and the last has -25 dB rejection for both second and third harmonics. The insertion loss of all filters is less than 0.6 dB with good agreement with simulation.