||With the popularity of modern wireless communication products, radio frequency front-end filter circuit plays a very important role, which is worthy of development and the value of research,especially multi-band pass filter.While the overall volume of the filter miniaturization is worth the effort. This paper proposes the use of a plane microstrip line resonator to design the application in the WLAN system (wireless local area network, WLAN) dual-band pass filter.|
Filter architecture proposed in the first band is designed at center frequency 2.45 GHz with 100 MHz bandwidth, the two sides of first passband both have transmission zero with the method of source-load coupling ,so that the passband with good selectivity. The second band designed from 5.15 GHz to 5.85 GHz, the center frequency 5.5 GHz with bandwidth 700 MHz is suitable of lots of countries in WI-FI / WLAN applications. The filter is coupled by dual-mode resonator which can use the equivalent circuit modal to analysis.By odd mode analysis , a quarter-wavelength resonator resonating at 5.5 GHz can be abstracted . By even mode analysis, a quarter-wavelength stepped-impedance resonator resonating at 2.45 GHz can be abstracted , and we can adjust impedance ratio
to control spurious response .We slot resonator and insert a open stub , which is from feeding line, into resonator in order to increase the amount of coupling. And we slot feeding line with spurline to improving selectivity of second passband. By using DGS(Defect Ground Structure), rejection band response can be improved after 7 GHz.