Compact 1.75–2.7 GHz Tunable BPF With Wide Stopband Up to 9.5 GHz Using Harmonic-Controlled SIDGS Resonators

In this brief, a harmonic-controlled substrate-integrated defected ground structure (SIDGS) resonator with tuning capacitor is proposed for the design of tunable filter. Such exhibits characteristic. The fundamental resonant frequency can be properly tuned, while spurious resonance controlled at much higher to achieve wide stopband. To verify principle, bandpass filter (BPF) designed and fabricated based on resonator. center tuned from 1.75 2.7 GHz. Meanwhile, stopband extend up 9.5 GHz rejection level 20 dB all cases. BPF also low insertion loss (i.e., 1.1–1.9 dB) compact size 0.07 ${\lambda _{g}}\,\,{\times }\,\,0.08\,\,{\lambda _{g}}$ , where microstrip guided wavelength GHz).