Flexible Design Method for Microstrip Bandstop, Highpass, and Bandpass Filters Using Similar Defected Ground Structures

It is well known that the typical low-pass characteristics can be obtained by a cascaded structure of alternating high- and low-impedance transmission-line (TL) segments. On the contrary, this paper focus on modifying this stepped impedance TLs to obtain the bandstop, highpass, and bandpass responses. A basic structure consisting of dumbbell-shaped defected ground structures (DGSs), complementary split ring resonators (CSRRs) DGSs and interdigitated coupling structures is proposed, which can simultaneously satisfy the design of different types of filters. Then, open stubs and short stubs are appropriately selected and achieve the necessary flexibility among the conversions of different frequency responses. Furthermore, different units are ingeniously embedded into the stepped impedance TLs to obtain good performances and small dimensions. By employing the extracted parameters and equivalent circuits, different types of frequency responses are well explained. Finally, the proposed filters are fabricated and measured, the measured results show a great agreement with simulated results.