Design of Quasi-Lumped-Element Filters and Directional Couplers using Multilayer Technologies

Abstract

The LTCC and sandwich multilayer technologies as applied to design of quasi-lumped-element passive microwave devices are considered. Design of miniature high-performance bandpass filters and directional couplers for wireless applications is presented. IntroductionAllocation of passive components within several layers of integrated circuit allows designing very compact highly-integrated microwave devices. Two different thick-film technologies are suitable for manufacturing multilayer microwave integrated circuits (MICs).The Low-Temperature Cofired Ceramics (LTCC) multilayer technology is widely used for realization of passive microwave devices and integration of active and passive devices into miniature front-end modules of low cost [1]- [3]. In the LTCC process conductive patterns are deposited by screen-printing onto thin (100-200 µm) dielectric sheets, which are then stacked up, laminated, and fired simultaneously [4].Application of the sandwich multilayer technology to realize passive microwave components and devices were reported in [6]- [8]. The sandwich process [5] employs a thick (0.5-1.0 mm) ceramic substrate as the core of multilayer structure. Conductive and dielectric layers are patterned onto this substrate by means of screenprinting technique. The layers are deposited in a "series" manner with consecutive co-firing of each layer. A number of layers can be printed in different areas on both sides of the ceramic substrate. Typical thickness is 15 µm for the conductive layers and 45-60 µm for the dielectric ones. Smaller thickness of dielectric layers with respect to LTCC materials allows decreasing the area occupied by parallel-plate capacitors. At the same time, parasitic grounded capacitances are sufficiently eliminated, if through a thick substrate. The ceramic substrate employed in the sandwich structures could also play the role of PCB, onto which a front-end module is assembled. Furthermore, the sandwich process is compatible with planar thin-film technology.Both the LTCC and sandwich technologies are suitable for a realization of compact, free of spurious response microwave devices based on quasi-lumped elements. This paper presents the design of miniature bandpass filters and directional couplers for wireless applications realized using the both multilayer technologies.