Advanced Techniques for Steerable Antennas

This document presents the activities carried out during the three years of my Doctorate of Philosophy. All chapters refer to separate topics fitting in the main subject of this Ph.D., whose focus is on techniques for steerable antennas. There are two main kinds of beam steering technologies: mechanical and electronic steering. The former is based on moving mechanical parts of the antenna or motions of the whole antenna itself, while the latter is accomplished by changing some electrical parameters of the antenna, without physically moving it. In this Ph.D., both technologies were investigated. In Chapter 1, a phased array antenna for space debris detection is studied. The antenna lattice is optimized to minimize the number of array elements, and in turn, the cost of production, while, at the same time, preventing grating lobes from being visible. The project, done in cooperation with the European Space Agency (ESA), leads to a totally analytical procedure to find out the best array lattice based on a few input parameters such as the size of the sky window the array should scan and the antenna electrical size. A methodology is developed to compute the optimal lattice parameters controlling, at the same time, the level of grating lobes. In Chapter 2, a beam-wave-guide antenna architecture is presented to accomplish mm-wave imaging of standout targets for weapon detection. A scanning method based on a small rotating mirror allows the antenna beam to scan a prescribed field of view, where the target is expected to be located. The idea of the system is to dynamically scan moving targets in a complex open environment with multiple moving human beings. In this Ph.D., a feasibility study of the system is presented with preliminary electromagnetic simulations and theoretical calculations. The limitations of this antenna architecture were highlighted with considerations on the achievable power budgets in the round trip way of the electromagnetic wave 7 Abstract from the transmitter to the target and back to the receiver. In Chapter 3, a simple scanning mechanism based on a double dielectric wedge placed above a flat-panel array antenna for satellite communications on the move (SOTM) is described. The dielectric superstrate is analyzed and designed to have a low profile, according to the application. The dielectric wedges are covered with an anti-reflection coating, which is designed in a completely analytical way, finding closed-form expressions for the electromagnetic and geometrical parameters of the coating layers. The beam scanning functionality and the anti-reflectivity of the coated wedge are simulated on MATLAB according to the transmission matrix theory and on commercial full-wave electromagnetic simulation softwares. Results show a proper operation of the system, with the possibility to manufacture a prototype by using 3D printing technology. Eventually, in Chapter 4, an error model of a multi-mode monopulse tracking receiver is built up to study the problems of tracking performance degradation seen in many ground stations belonging to ESA tracking network (ESTRACK). These antennas scan the beam in a mechanical way using elevation and azimuth motors to keep the antenna on the target direction. The radiation characteristics of the circular waveguide fundamental and a few higher-order modes are deeply understood and the operation of a multimode monopulse receiver is analytically described in detail. An error model is constructed on MATLAB based on the scattering parameters of ideal and simulated microwave components composing the monopulse chain. Amplitude and phase unbalance factors are also introduced in the model to see the effect of such non-idealities on the tracking performance. Results prove that some unbalances can, indeed, produce the same effects as measured in ESA stations.