| Summary: | This paper describes the implementation of a miniaturized quad flat no-lead (QFN)-packaged bandpass filter (BPF) with a combination of an intertwined circular spiral inductor and two types of integrated center-located capacitors using gallium-arsenide-based integrated passive device (IPD) fabrication technology. Air-bridge structures were introduced into the outer circular spiral inductor to save space and to provide the filter with a compact chip area of 1192.5 × 1012.7 μm<sup>2</sup>. An equivalent circuit was modeled, the current density and variable dimensional parameters were simulated, and the fabrication process was introduced to achieve a better understanding of the IPD BPF. The proposed device was packaged using the QFN-packaging technology and was measured to possess a single passband with a central frequency of 1.91 GHz (return loss: 28.8 dB) and a fractional bandwidth of 72.69% (insertion loss: 0.62 dB). One transmission zero was obtained on the right side of the passband at 4.78 GHz with an amplitude of 35.95 dB. The fabricated BPF can be used in various L-band applications, such as mobile service, satellite navigation, telecommunications, and aircraft surveillance, due to its miniaturized chip size and high-performance characteristics.
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