Miniaturised wideband bandpass filter with good selectivity based on 3D heterogeneous integrated passive device technology

The miniaturised wideband filter with good frequency selectivity and wide stopband is proposed, which is based on three-dimensional (3D) heterogeneous integrated passive device technology. The proposed sixth-order wideband bandpass filter is based on the magnetic-coupling-loaded highpass-lowpass lumped topology and implemented by the 3D heterogeneous integration process, integrating GaAs-based and Glass-based micro-nano-scale processes together. Then, lumped inductors are designed in the Glass substrate with low dielectric loss tangent and realised by a three-dimensional spiral structure. Therefore, the inductors have high quality factors and small sizes. The lumped capacitors are designed using the GaAs thin film process. Finally, a prototype with a 3-dB fractional bandwidth of 42% is designed and fabricated at 3.875 GHz (f₀). The upper-stopband attenuation higher than 30 dB is extended to more than 5.15f₀. It occupies only 0.014 × 0.018 λ₀² (1.1 × 1.42 mm²), where λ₀ is the free-space wavelength at f₀.