The proposed research pertains to the understanding and modelling of integrated circuit discontinuities (such as coax to microstrip) and printed circuit antennas for microwave and millimeter wave applications. Recent advances by the PI in studies of integrated circuit antennas, for example, have shown that a two layer substrate-superstrate configuration can yield advantages in higher gain, efficiency, pattern omnidirectionality, and bandwidth. Most materials in use as substrates have anisotropy which if neglected in modeling contributes to errors that increase with frequency. It is important to obtain accurate frequency dependent modelling of these effects in order to provide the efficient computer-aided-design (CAD) algorithms needed in the development of very high frequency monolithic device.