The Design of a Compact, Wide Bandwidth, Non-Foster-Based Substrate Integrated Waveguide Filter

A compact, wideband, half-mode substrate integrated waveguide (HM-SIW) filter with internal non-Foster element is demonstrated. First, its passive version is simulated and measured. Next, by integrating an ideal tunable capacitor at the end of the central stub of the HM-SIW resonator, the frequency-agile characteristic of the tunable HM-SIW filter is investigated. Finally, a negative impedance converter (NIC) is developed to replace this tunable capacitor to design a new nonFoster filter. The non-Foster-based HM-SIW filter was realized. Its measured results indicate that it has an operational fractional bandwidth of 10.8% and an electrical size 0.118×0.292 λ_g², which is a 3.93 times bandwidth increase and a ~12% electrical size reduction compared to its passive, fixed capacitance version.