Analysis and Application of 3-D LTCC Directional Filter Design for Multiband Millimeter-Wave Integrated Module

In this paper, we describe a systematic design and analysis procedure towards the successful implementation of 3-D low-temperature cofired ceramic (LTCC) multilayer loop directional filters at millimeter-wave frequencies. Directional filters represent a fundamental building block combining multiple filtering for mixing and multiplexing operations, hence reducing complexity while maintaining compactness. In this paper, different vertical coupling schemes are realized in order to implement the directional filters with the different performance optimums. The further use of the rectangular loop has been demonstrated as the optimum topology leading to the best performances. The filters have been measured to have less than 2.5-dB insertion loss in the bandpass path and higher than 25-dB rejection at 40 GHz, while occupying an area of 1.7times1.7 mm². They demonstrate 4.7%-6.3% fractional bandwidth with better than 20-dB isolation. 40-GHz multiplexers for multiband applications with 4-GHz/8-GHz frequency separations have been designed and measured to have approximately 3-dB insertion loss in each band with better than 20-dB isolation between the outputs in passbands. This is the first complete report on LTCC directional filter-based designs towards the system-on-package (SOP) solution for the multiband millimeter-wave wireless modules