A Miniaturized On-Chip BPF With Ultrawide Stopband Based on Lumped Pi-Section and Source-Load Coupling

In this letter, an on-chip bandpass filter (BPF) with ultrawide-stopband and high selectivity is designed and manufactured by 2-mu m gallium arsenide (GaAs) HBT technology. For the sake of selectivity and rejection of the BPF, an extra pair of transmission zeros (TZs) locating at both sides of the passband is produced by introducing source-load coupling. Moreover, to improve the rejection of the BPF, a Pi-section circuit is designed so that a TZ is obtained at the upper sidebands. The measurement results show that the bandwidth covers 2.4-4.3 GHz, while its insertion loss is 2.05 dB at 3.35 GHz. In addition, this BPF achieves more than 30-dB sideband suppression format both at 0-1.3 GHz and 5.6-40 GHz. The BPF size is very compact only, i.e., 0.6 mm x 1.5 mm (0.02 lambda g x 0.05 lambda g); to the best of our expertise, this is the widest sideband suppression with such a compact on-chip size.