A layout efficient, vertically stacked, resonator-coupled bandpass filter in LTCC for 60 GHz SOP transceivers

This paper describes the design and implementation of a layout efficient bandpass filter implemented in Low-Temperature Co-fired Ceramic (LTCC) substrates. Applications for this filter include band select filters for 60 GHz System-On-Package transceivers. Two bandpass filters based on a quasi-elliptic configuration were implemented here using four half-wavelength resonators. The first filter uses all planar resonators to achieved a measured insertion loss of 3.7 dB and a return loss > 10 dB and with a layout area of 1.263mm
²
. The second filter uses vertical stacking of two of its resonators to reduce the layout area and achieved higher immunity to process variations. Measurements for the second filter show an IL of 3.4 dB while maintaining a RL > 10 dB. The vertically stacked filter consumes a layout area of 0.811mm
²
, corresponding to a layout reduction of 36% compared to the planar filter with performance less prone for process variations.