Description
Microwave circuits play a pivotal role in satellite and 5G communication systems. In these contexts, this activity is focused on the modeling, design and experimental characterization of microwave circuits.
Circuit design mainly concerns power microwave amplifiers based on GaAs and GaN technologies, as well as modeling and design of both RF/baseband predistortion stages, and of other functional blocks (mixers, oscillators, LNA). Multistage high power (>100 W), high frequency amplifiers are investigated using conventional approaches and innovative strategies, e.g., the Doherty scheme. Linearity is a crucial requirement, both in ground and space segments. This requires, e.g., to combine (and optimize) system-level metrics such as the noise power ratio (NPR), and circuit-level metrics such as AM/AM and AM/PM conversions, and intermodulation distortion. The capacity of an RF power amplifier to tolerate load variations is of paramount importance in modules operated in wireless communication systems, since changes in the load impedance can occur due to variations in antenna impedance or environmental conditions. To achieve this goal, various techniques are investigated, such as tunable matching networks, both active and passive, adaptive impedance, and supply control.
The availability of RF and microwave on-wafer measurement systems able to give all possible information on the devices under consideration is mandatory for circuit and system design. Large breakdown voltage devices, e.g., GaN-based, deliver larger output power, and the test setups must be properly designed for high power handling. Moreover, the common use of wideband complex modulations introduces issues concerning the measurement of microwave performance, the adjacent channel power ratio, and the realization of wide band variable loads. Also, the spread of differential devices in handsets and base stations has triggered the need for non-linear multiport characterization, which is at the frontier of large signal microwave measurements. On the basis of wafer-level characterizations carried out up to 18 GHz (power load-pull measurements), 40 GHz (two-port measurements) and 110 GHz (one-port measurements), circuit-oriented models based on black-box approaches (behavioral models) or equivalent circuit approaches (small- and large-signal) are developed to assist the circuit- and system-level computer-aided design.