NOVEL IN-LINE MICROSTRIP COUPLED-LINE BANDSTOP FILTER WITH SHARP SKIRT SELECTIVITY

This paper presents a novel design approach to design in- line microstrip bandstop fllter with accurate design theory and sharp skirt selectivity. This kind of bandstop fllter is based on a simple coupled-line structure, indicating compact and ∞exible circuit layout for microstrip implementation. For a single-section bandstop fllter, the scattering parameters and their constrain conditions are achieved, which provides an efiective design guide for multi-section bandstop fllters. Theoretical analysis indicates that the even-mode and odd- mode characteristic impedances can be easily used to determine the desired bandstop performance while the total circuit layout keeps very compact. For demonstration, seven numerical examples are designed, calculated, and compared. Finally, both experimental and simulation results of a two-section two-cell microstrip bandstop fllter operating at 1GHz are presented to verify the theoretical predications.