Miniaturized On-Chip Bandpass Filter With Multi-Transmission Zeros Using Interwound Winding Transformer

In this letter, a miniaturized on-chip bandpass filter (BPF) with multi-transmission zeros (TZs) is proposed in the gallium arsenide (GaAs)-based integrated passive device (IPD) technology. The proposed BPF consists of two symmetrical LC ring structures, which are connected by an interwound winding transformer (IWT). Three TZs are newly created by coupling capacitors between two interwound spiral inductors in IWT without adding extra circuit components. Through even- and odd-mode analysis, general simultaneous equations for the circuit parameters are newly derived. Two TZs in the upper stopband can be significantly tuned by adjusting the extra variable parameter (${L}_{{1}}$) without affecting passband performance. Considering the trade-off between achievable coupling factor, coupling capacitor and performance, narrower bandwidths are preferred for better RL and SR in fabrication. For validation, a prototype filter with a 3-dB fractional bandwidth (FBW) of 48.5% (3.9-6.4 GHz) is manufactured in GaAs-IPD technology. The measured BPF exhibits multi-TZs in the stopband and insertion loss is 2.25 dB at the center frequency${f}_{{0}} = 5$GHz. The filter has a compact size of$0.016 \; \lambda _{{0}} \times 0.007 \; \lambda _{{0}}$, where$\lambda _{{0}}$is the wavelength in air at${f}_{{0}}$.