This book focuses on RF specific modeling and simulation methods and the consideration of system and circuit level descriptions. It contains application-oriented training material for RF designers which combines the presentation of a mixed-signal design flow, an introduction into the powerful standardized hardware description languages VHDL-AMS and Verilog-A, and the application of commercially available simulators. Modeling and simulation must accompany the design steps from specification to overall system verification in order to bridge the gaps between system specification, system simulation, and circuit level simulation. Very high carrier frequencies together with long observation periods result in extremely large computation times and require specialized modeling methods and simulation tools on all design levels. The book is geared to graduate students and industrial professionals engaged in communication system design.