O ngoing developments in integrated circuit (IC) technology have resulted in fully integrated monolithic systems-on-chip (SoC). The state of the art of today's silicon-based semiconductor technologies, such as the silicon-germanium heterojunction bipolar transistor (SiGe HBT) and the silicon metal-oxide-semiconductor fi eld-effect transistor (MOSFET), allow for the low-cost fabrication of transceiver front-end circuitry with operating frequencies even above 100 GHz [1]. These key elements of silicon high-frequency semiconductor electronics have opened the door for the millimeter-wave consumer market in communication technology and sensor applications.After they are manufactured, RF and millimeterwave frontends and SoCs have to be tested for correct functionality and performance before they are passed on to the consumer. Testing of high-frequency blocks in radio-frequency integrated circuits (RFICs) is a complex, time-consuming, and costly task for engineers. External tests necessitate expensive, high-performance