Compact 60-GHz LTCC Stripline Parallel-coupled Bandpass Filter with Parasitic Elements for Millimeter-wave System-on-Package

This paper presents a compact stripline parallel-coupled bandpass filter with parasitic elements on a multilayer LTCC substrate. The parasitic elements are formed above and below the first section and the last section of the filter. These parasitic elements effectively increase the coupling between adjacent parallel lines, resulting in a compact and low loss filter. The proposed filter is fabricated on four layers of a 50-mum LTCC substrate. The intrinsic area of the filter is just 1.6 mm by 0.7 mm. A fabricated prototype three-pole bandpass filter chip achieves a center frequency of 59.1 GHz, a bandwidth of 6.9 %, and an insertion loss of 5 dB that includes input and output transitions. The return losses are below -10 dB in the pass band. The figure-of-merit of the fabricated bandpass filter is the highest of all reported 60-GHz-band filters even though it has the smallest size. The proposed filter well suits a highly integrated millimeter-wave LTCC system-on-package.