Novel compact wideband bandpass filter using microstrip and coplanar-waveguide resonators with good harmonic suppression

A compact wideband bandpass filter (BPF) is presented and experimentally validated in this letter. The described filter consists of microstrip resonator and CPW resonator designed on different layers, has compact size and strong coupling strength and then achieves good wideband performance. By adjusting the coupling electric length between resonators and the adding trapeze-form patch, good harmonic suppression can be expected. One prototype is fabricated and measured to demonstrate the validity of the design idea, good agreement with theoretical expectation can be observed. The measured insertion loss is less than 0.5 dB in the whole passband of 3.4-5.5 GHz (about 47.2% fractional bandwidth), and a wide stopband bandwidth with 20 dB attenuation goes up to at least 18.5 GHz. The second harmonic suppression is better than -35 dB (8.7 GHz), while the third harmonic suppression is better than -25 dB (13.3 GHz).