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In this paper, an improved bandstop filter (BSF) using defected ground structures (DGS) and defected a microstrip structures (DMS) is proposed. The shield current distribution effectively disturbed by the defected structure in a microstrip line yield added inductances and capacitances to the line. This change in nature of microstrip line is related to the slow wave factors and other parameter such as phase delay, phase constant, operating frequency etc. This new type of slowwave structures are called defected microstrip structure (DMS). Here a new spiral shaped structure with improved stopband filtering characteristics are introduced. A two-pole stopband response is shown by the frequency characteristics of the proposed spiral-shaped DMS unit. The equivalent L C parameters are extracted using proposed equivalent LC model. One such DMS units with HighLow impedance line on top plane along with a Pi-shaped DGS unit on the ground plane is used to design a bandstop filter having 10 dB rejection bandwidth of 75% and sharpness factor is greater than 63 dB/GHz at both edges.

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