Microwave filter design optimized for ceramic multilayer technique

Low Temperature Co-fired Ceramic (LTCC) is a proven packaging technology for microwave and millimetre-wave applications. Advanced low-loss material systems and improved manufacturing technology facilitate economic and highly reliable packaging solutions for automotive, telecom, medical and security applications. One of the virtues of LTCC is the option to integrate all kinds of components into the multilayer. Embedded passives include resistors, capacitors and inductors. Moving matching networks and filters into inner layers is further increasing density of integration. Microwave filters in LTCC can be used as an integral part of a larger package but also as single components mounted as drop-in or SMT. Ceramic multilayer technology allows for new filter concepts with three-dimensional routing and integration. Tolerances in material properties and manufacturing are challenges to be met with the design and production of microwave filters. Tape thickness, permittivity, shrinkage, registration of conductor pattern to via position, conductor width and thickness are some of the parameters that influence filter performance and reproducibility. This paper shall compare two different concepts for a 20 GHz band pass filter regarding their sensitivity to manufacturing tolerances. An optimized filter design shows improved robustness against manufacturing tolerances. This concept particularly reduces the sensitivity to registration tolerances of conductors and ground vias. A filter synthesis and simulation which takes into account systematic and random manufacturing effects takes out some of the guesswork of filter design and fabrication. It will also reduce the trial and error loops traditionally involved with this part of microwave engineering. Keywords: LTCC, Multilayer Ceramics, Manufacturing Tolerances, Yield Enhancement, Microwave Bandpass Filter.