The Design Of CPW Wide Stop-band Low Pass Filter

The planar integrated microwave circuits play a very important role in modern communication technology. The Coplanar Waveguide structure has the advantages of simple process, low cost, large integrated circuits and good dispersion performance, so it has been widely used in modern wireless communication filter design and has become a hot research field of microwave integrated circuits.In this paper, a study based on the basic transmission theory and microwave filters is presented, the resonance condition of λ/4stepped impedance resonator unit and the properties of DGS structure is analyzed, then the analysis of unit structure measurement is introduced. After using cascade structure circuit of λ/4stepped impedance resonator unit、coplanar waveguide defected ground structure (DGS) unit and semicircular stepped impedance minor structure, a sharp cutoff and wide resistance band low-pass filter is constituted. And by processing fractal structure on λ/4stepped impedance resonators and improving the stepped impedance construct of filter, compared optimized by HFSS simulation software, a compact and wide stop-band low-pass filter is designed. The Cut-off frequency is3.5GHz, the largest passband insertion loss is-1.3dB, the passband standing wave ratio is less than1.7dB, the resistance band suppressed from the3.8GHz to17GHz is more than20dB and the size of the final CPW filters to25mm x18mm,The measured results of the filter show consistent match with its theoretical ones. Finally, the shape of wang and its improved low-pass structure is presented, and the effect of its physical size on the electrical properties is analyzed. Also through shape of wang with DGS, the low loss and wide stop band low-pass filter is designed. And then through the stepped impedance matching to improve its passband insertion loss and return loss, and a wide stop-band filter is completed based on optimize and simulation of HFSS.The simulation shows, The Cut-off frequency is2.5GHz, the largest pass band the return loss is more than20dB, the largest insertion loss is-0.5dB, the stop band ranges from3.0to17GHz, and the size of the final CPW filters to20mm×30mm, and so low loss and broad stop-band filter is realized.