An embedded LTCC stripline bandpass filter for millimeter-wave system on package

This paper presents a low temperature co-fired ceramic (LTCC) bandpass filter, which is embedded into an eleven-layer substrate. A quasi-coaxial structure is employed to reduce the impedance discontinuity caused by GCPW to stripline transition. Vertical metal vias are utilized to realize grounding and shielding for the stripline filter. The measurements of the fabricated filter show an insertion loss of 4.5 dB and a 1.73 GHz passband with the centre frequency at 34.69 GHz, including the two RF coaxial connectors. The measured return loss in the passband is lower than -13.45 dB. The whole bandpass filter occupies an area of 9.8 mm × 5 mm × 1.1 mm. The compact configuration and measured performance show that the filter is suit for millimeter-wave system on package.