Synthesis of Bandstop Filters With Ultra Wide Upper Passbands

Compact Bandstop Filters with Extended Upper Passbands

“…The conventional microstrip-based bandstop filter can be derived from the lowpass filter (LPF) prototype. The design starts with n-section low pass filter in the form of shunt capacitors and admittance inverters [1,9,10] as shown in Figure 1. A suitable frequency transformation [1,10] converts the shunt capacitors of the LPF prototype circuit to a series resonance circuit at the fundamental frequency that could be implemented by open circuit microstrip stubs as shown in Figure 2.…”

“…LP prototype to distributed element BSF mapping resulting in circuit made up of OC and SC stubs and ideal inverters could be, effectively, employed as described in [9]. This transformation converts the shunt capacitors into shunt arm series OC and SC stubs.…”

“…The transmission zeroes formed by the distributed resonators in the BSF basic circuit shape the stopband response of the filter [1,2,9,10]. Based on that, new shaped structures of compact bandstop filter sections are presented in this paper.…”

“…The upper stopband center frequency has been extended to six times the fundamental stopband center frequency by a new design procedure that uses coupled line configuration with the open stubs replaced by loading capacitors. More recently, this ratio has been improved to 18 times the main stopband with realizable element values [9]. In the basic design of [9], resonators made up from commensurate open circuit (OC) and short circuit (SC) stubs coupled by inverters are used.…”

“…More recently, this ratio has been improved to 18 times the main stopband with realizable element values [9]. In the basic design of [9], resonators made up from commensurate open circuit (OC) and short circuit (SC) stubs coupled by inverters are used. The inverters are, then, converted into proper number of unit elements (UE) which increase the degree of the filter and contributes to the filter response considerably upon optimization.…”