Reduced-size wideband bandstop filter using two open-circuited shunt stubs spaced by a double-length transmission-line element

A reduced-size bandstop filter is proposed using two meandered or bended λg/4 open-circuited shunt stubs. A double-length transmission-line element (TLE) is used as a connecting line between these stubs in order to obtain a wider stopband than that of the conventional filter with a single-length TLE. The meandered or bended double-length connecting line has a length of λg/2 and the same characteristic impedance as the open-circuited shunt stubs. A simple transmission-line model is used to calculate the frequencies of the attenuation poles and zeros. Finally, three wideband microstrip bandstop filters are designed and realized with the same stopband characteristics. It is shown that the smallest of the proposed filters occupies a smaller surface area than (λg/5)2. The wideband bandstop filters are also evaluated via experiment and simulation with very good agreement. © 2004 Wiley Periodicals, Inc