A harmonic-suppression microwave bandpass filter based on an inductively compensated micro strip coupler

In this paper, a novel harmonic-suppression bandpass filter based on an inductively compensated microstrip coupler is presented for wireless/microwave applications. The compensated inductors are connected at coupled and direct ports to improve the directivity of the microstrip coupler for more than 30dB. This directivity enhanced microstrip coupler is used as a basic building block to design a 1.8GHz microstrip bandpass filter. The filter insertion loss is well below 2.2dB, while the input and output return losses are less than 13dB over the bandwidth. The harmonic suppression at the 1st and the 2nd harmonics are more than 49.98dB and 34.21dB, respectively.