Compact Bandstop Filter with Multiple Rejection Zeros

This paper presents a compact band stop filter (BSF) based on the dual metal plane configuration with multiple rejection zeros (RZs). Quasi-lumped technique with novel patch-via-spiral dual mode resonator is applied to the design of the proposed filter. Multiple rejection zeros are introduced by open-end stubs for high selectivity. Design equations are obtained by using a lossless transmission line model. The calculated results show that the lower and upper rejection zeros can be easily tuned by the coupling capacitor and the open-end stubs respectively. By using the Microstrip-Coplanar-Waveguide (CPW) structure, the size of the proposed filter can be reduced to 12.8 mm x 9 mm(i.e., 0.24 x 0.17), where denotes the guided wavelength at center frequency.