Millimeter-wave applications above Ka-band have become increasingly important for both the military and commercial sector. With the overcrowded spectrum at lower microwave frequencies, more systems are demanding the use of unlicensed spectrum space at V-, W-band and beyond. Data communications for wireless links are requiring frequencies greater than 75 GHz to achieve high data rates up 80 Gbps. Scalable W-band phased arrays using silicon technology have been demonstrated for automotive radar, imaging and communication. Technologies such as Gallium-Nitride (GaN) have been pushing high-frequency performance with operating frequencies in the hundreds of GHz allowing the capability for solid-state high-power transmitters. General challenges forW-band high-power solid-state transmitters are achieving high effective radiated power (ERP) in a small footprint and with reasonable efficiency for space constrained applications. Recent advances in GaN technology with cutoff frequencies ft > 150 GHz achieve power densities as highas 3W/mm at W-band. For very high-power applications many amplifiers are required to be combined and fed into an array for spatially coherently power combining. The need for multiple levels of power combining provides a trade off in terms of combining efficiency, heat dissipation, volume and co-design from the transistor to the radiating aperture. Each power amplifier (PA) module can have varying levels of power combining including device level within a monolithic microwave integrated circuit (MMIC) amplifier, thin-film and waveguided power combining, and spatial power combining to achieve the desired ERP.
This thesis focuses on the design and analysis of millimeter-wave MMIC power amplifiers for high effective radiated power (ERP) using three GaN research processes in development by the industry. W-band PAs are presented and predict state-of-the-art output power. Analysis of power combining efficiency anddegradation in power combiners and phased arrays caused by GaN-on-SiC semiconductor process variations is presented.</p
