Extracting of compact tunable BPF from LPF using single T-DGS-resonator and 0.25PF/0.5PF Chip Monolithic Ceramic Capacitors

A novel compact defected ground structure (DGS) lowpass filter (LPF) and tunable bandpass filter (BPF) are proposed in this paper. The designed filter consists of one TDGS resonator, which is excited by 50 ohm microstrip line, placed on top layer between the input and output this structure. The addition of compensated patch capacitor improves the low insertion loss and ultra-wide stopband with 15 dB attenuation from 2.2 GHz to 3.6 GHz. The size of the proposed filter is very small (0.023 λg ç 0.044 λg, with λg = 0.263 m). The tunable BPF is extracted from LPF topology using variable Chip Monolithic Ceramic Capacitors and J-inverter technique. The measured and the EM simulated results are presented and discussed.