Design of Wide Band-Rejection Filter using All-Stop Parallel Coupled Line Canonical Form along with Transmission Line
Keywords:Band-pass filters, band-reject filter, parallel coupled lines, scattering parameters, transmission line theory
Microstrip parallel coupled lines in two-port canonical forms are used extensively in the design of bandpass and bandstop filters.
Two parallel coupled lines form a four-port network and it can be converted into a two-port network by terminating two of the four ports either with open or short circuits or by connecting the two ends. There are ten two-port canonical forms for a four-port parallel coupled line structure. Out of these ten forms, three forms are all-stop in nature. These all-stop parallel coupled line circuits are never used in the design of filters due to high insertion loss over the entire periodicity. Parallel coupled lines are periodic with half-wavelength. Hence, the theme of this paper is to propose the usefulness of the all-stop parallel coupled lines in the design filters by connecting this all-stop parallel coupled line structure with a transmission line in parallel. Analysis has been carried out on this basic structure of all-stop parallel coupled line along with the transmission line to characterize over a period. After the analysis, it has been proposed that this composite structure can be used in the design of bandstop filters.
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