Compact Mechanically Tunable Microstrip Bandstop Filter With Constant Absolute Bandwidth Using an Embedded Metamaterial-Based EBG

A mechanically tunable, constant-absolute-bandwidth (ABW) bandstop filter is realized using the metamaterial-based electromagnetic bandgap structure (MTM-EBG). The MTM-EBG is embedded within a microstrip (MS) line and used to produce a bandstop filtering response, with a topology that is compact, uniplanar, and fully printable. A three-cell MTM-EBG-based MS bandstop filter is designed and experimentally verified for operation centered at 4.18 GHz with a 10-dB rejection bandwidth of 247 MHz. This filter is then made tunable by placing a dielectric plate directly on the surface of the MTM-EBGs. Moving this plate across the surface of the MTM-EBGs changes their reactive loading and, consequently, shifts their response. To ensure a constant ABW, the dielectric plate is perforated to produce an effective plate permittivity that varies for each unit cell. The tunable filter is then fabricated, with the dielectric plate applied to the MTM-EBG-based bandstop filter using a 3-D printed superstructure. A tuning range of 3.80 GHz ± 6.2% and a 10-dB bandstop ABW of 244 MHz ± 1.3% are demonstrated, showing good agreement with the simulated data. The MTM-EBG-based tunable bandstop filter has a variation in ABW comparable to 3-D filters (which typically have substantially lower variation in ABW than fully planar filters) while occupying substantially less area than alternate planar realizations.