Tunable SIW Bandpass Filters With Improved Upper Stopband Performance

This brief propose the design and measurement of tunable, highly selective and wide-stopband microwave filters using substrate integrated waveguide (SIW) technology. A two pole filter is designed using optimized cavity parameters. Two higher order (4-pole) filters are designed by connecting two cavities vertically and horizontally through coupling slots. In this way, four poles are achieved in two cavities, in which the proposed filter produces 2xN poles in N cavities. A varactor diode is employed in both configurations to make the filters tunable. The proposed filters have wide upper stopband performance [20 dB up to 4.8f1 (Filter 1) and 20 dB up to 4.2f(1) (Filter 2)], lower insertion losses [0.2-1.1 dB (Filter 1) and 0.2-1.5 dB (Filter 2)] and good tunability ranges [2.7-3.4 GHz (Filter 1) and 3.1-3.9 GHz (Filter 2)]. In order to validate the proposed design, a prototype is fabricated on RT/duroid 5870 substrate and measured. The simulated results accord closely with the measured results.