Multifunctional substrates for high-frequency applications

A substrate that is designed to suppress parasitic modes while at the same time provides high-Q filtering capability is presented. High-density circuits require the integration of multiple functions in very limited space. More specifically, with the design of three-dimensional (3-D) circuits, parasitic effects caused by the excitation of surface waves result in a serious degradation of performance and impose limitations on circuit density and performance. Herein, an effort is presented to use advanced design concepts to enable embedded functionality within a substrate. The presented substrate geometries can easily be extended to 3-D to allow for the development of system-in-a-package which incorporates a high-Q filter bank to provide effective frequency selectivity. To demonstrate this concept, resonators and filters in LTCC are designed, fabricated and measured. Resonators in LTCC with unloaded Q up to 428 were measured. A narrow-band 2-pole filter is realized to show that a function of a relatively high-Q can be incorporated into the packaging. The 2.28% filter has an insertion loss of 1.7 dB due to the low loss nature of the design. Simulation and measurement of the structures are presented with good agreement achieved.