Miniaturisation of a LTCC high-frequency rat-race-ring by using 3-dimensional integrated passives and embedded high-k capacitors

Some of the trends in the communication industry consist in increasing the variety and/or number of integrated functions in portable devices as well as reducing their size. Because of these trends, forthcoming portable wireless devices have to comply with more demanding hardware requirements, especially regarding higher wiring densities and miniaturisation level. A suitable combination of system architecture, substrate technology, integrated materials with improved functionality and substrate design is crucial for enhancing the level of miniaturisation in RF-electronic circuits. In this paper the miniaturisation of a rat-race-ring for 2.45 GHz (free-space wavelength of about 122 mm, Bluetooth and WLAN applications) with embedded lumped-elements in low-temperature co-fired ceramic technology is discussed and the results are presented. The rat-race-ring was realised in three different topologies. The first version was realised using a quasi-planar architecture. Using this architecture a device size of 7.5 times 7.5 mm² was achieved. The second version of the rat-race-ring was designed as a module with three-dimensional fully integrated passives and land-grid-array (LGA) solder pads. Using this topology the size of the device was reduced to 3.8 times 3.8 mm². In the third design the capacitors were implemented using locally integrated thin high-k dielectric patches. The whole size of this LGA-module (third device) amounted to 2.4 times 2.4 mm², which implies an area miniaturisation to ten percent of the size of the first design. In this paper technological and design issues as well as numerical simulations and measurements of the microwave scattering parameters are considered and discussed.