Books in the Science for systems series

One of the most dangerous situations when flying a helicopter is landing over dry sand or powder snow. The rotors swirl particles creating a dense cloud. With optical methods navigating through this cloud is impossible but for millimetre waves it becomes almost transparent. As a consequence millimetre waves are an outstanding choice for the development of imaging systems that can be used as a landing aid. The aim of this work is the 3D imaging of static scenes with a large field of view, good resolution and high dynamics. In this thesis a demonstrator system is presented, which is based on the MIMO principle and works with FMCW radar modules in the millimetre wavelength range. The set-up of the demonstrator system is explained and the hardware components are described. An algorithm for image reconstruction is presented as well as a calibration routine. An optimized antenne aperture is determined that enables unambiguous imaging of the half-space in front of the aperture with good resolution and low side lobes. Various measurements illustrate three-dimensional imaging capabilities and show long-range operation. In addition, the data acquisition rate is determined.

The rapidly-growing data throughput rates in a wide range of wireless communication applications are pushing the established semiconductor device technologies to their limits. Considerably higher levels of solid-state output power will therefore be needed to meet the demand in the next generation satellite communications as well as the RADAR systems. Owing to their superior material properties such as high breakdown fields and peak electron velocities, GaN-based high electron mobility transistors (HEMTs) have recently prevailed in high-power systems operating in the microwave frequency bands. On the other hand at the millimetre-wave (MMW) and sub-MMW frequencies, highly-scaled GaN HEMTs are prone to experiencing deteriorated high frequency characteristics which severely limit the high-power performance. In an attempt to overcome this, 3-dimensional GaN HEMT devices featuring the Tri-gate topology are developed in this work, exhibiting enhanced performance in terms of both off- and on-state figures of merit. The demonstrated results promote the great potential of Tri-gate GaN HEMTs for both MMW power amplifier and high-speed logic applications.