Wideband BSF Using Coupled Stepped Impedance Hairpin and Interdigital Capacitor

摘要

A compact bandstop filter (BSF), using a coupled stepped impedance hairpin unit and an inner interdigital capacitor, is presented in this article. Detailed theoretical analysis reveals that the filters bandwidth and stopband rejection level can be controlled by the upper transmission line's characteristic impedance, the capacitance or the coupling strength of the coupled line. Based on this theory, a proposed BSF centered at 2.22 GHz with a bandwidth of 81.08 percent has been designed, fabricated and measured. The implementation area is 0.141 λg × 0.158 kg, where λg is the guided wavelength of a 50 Ω, transmission line at the center frequency. Good agreement between measured and simulated results is obtained.