MULTILIB is a new, state-of-the-art model library for multi-layered circuit technologies. It includes all standard elements for analog high-frequency multi-layered circuit designs, such as multi-metal-level ICs, PCBs, LTCC and softboard substrates, etc. The MULTILIB modeler library employs the User-Compiled Analog Model interface of Agilents ADS circuit and system simulator software and it is thus fully integrated in Agilents ADS. All elements are available by the well-known component-palette concept in Agilents ADS as usual. Speed and accuracy are granted by using an efficient implementation of the Finite-Difference-Time-Domain (FDTD) method. Tunig, optimization and layout capabilities are integrated as well.