Dual-band Filter Based On The Frequency Transform

Dual-band filters have been gaining wide attention in recent years as one of the mostimportant circuit blocks in exploring dual-band wireless systems. The design of dual-bandfilters based on the frequency transformation is researched in the thesis, completing withthe material object development of two dual-band bandpass filters and one dual-bandbandstop filter, moreover, frequency restriction which is introduced while empolying thedistribution parameter to realize lumped parameter is analyzed.First, the basic theory of microwave filter is introduced as the fundamental theory forthe dual-band filter research. Then, the material object development of the dual-bandbandpass filters which are composed by the microstrip quarter-wavelength open stubs andthe microstrip quarter-wavelength lines or the microstrip quarter-wavelength short stubsand the microstrip quarter-wavelength lines are carded on, the test result andelectromagnetic field simulation result shows a good agreement. Moreover, the method togain two equal fractional bandwidths of the two bandstops is proposed, which is adjustingthe center frequency of the microstrip quarter-wavelength open stubs or the microstripquarter-wavelength short stubs.Otherwise, one kind equivalent network circuit which transfers series-LC resonatorand parallel-LC resonator in the shunt branch to two parallel-connected series-LCresonators is inferred, and thus another topology of a dual-band bandstop filter realizationis proposed. The material object test result and the electromagnetic field simulation resultshows a good agreement by carrying on the material object development of the dual-bandbandstop filter, which confirms the feasibility of this filter.