Methodologies for Military Applications in Propagation Prediction and RCS Reduction

Being an officer of the Italian Navy, I am involved in research and field-testing activity that takes place in the CSSN-ITE Institute (Centro di Supporto e Sperimentazione Navale – Istituto per le Telecomunicazioni e l’Elettronica), in which I am currently employed. There, I have had the opportunity to use and study several pieces of interesting technology, ranging from drones to Software Defined Radio (SDR) waveforms and advanced beamforming communication kits. Another of the points of interests of the ITE Institute is live testing and calibration for ship equipment, performed on military ships during their lifecycle. Being very complex systems, ships are in a way like human beings, and their radio and radar systems need continuous check-ups to be maintained in full efficiency. Because of this, and because of the very convenient position of the ITE building (which is right on the seaside), several times per year different ships will visit us and have their radar, communication, electronic warfare and auxiliary systems measured and, where necessary, fixed. Their radar cross section and infrared signatures will also be measured, updating the reference data each ship is given right after its construction. This thesis is organized into three main chapters. The first chapter acts as an introduction, and tries to give some context about military research, detailing the application areas for the work presented in the following two chapters. Military ships are of course very appealing for blue waters measurements: that is the idea behind the second chapter, in which the Long Term Evolution (LTE) cell of the ITE Institute was used to test LTE capabilities in short, medium and long range scenarios, laying the foundations for the hybrid method-of-moments/ray tracing prediction model that is later presented, along with several of the gathered network and physical layer statistics. The idea behind this method is that, in order for predictions to match the measured path loss, the estimation has to account for electromagnetic interactions of the antenna with all kind of metallic structures in its proximity, which will considerably alter the radiation pattern. This knowledge had been soundly developed after years of measuring and storing radiation patterns of communication systems installed on actual ships in the sea, but is not typically considered in propagation data gathering. CSSN-ITE is also very concerned with radar cross section reduction. We have seen and measured how antennas (and in particular parabolic reflectors) can act as hot spots, sending incident radar waves straight back to the emitter, resulting in very high radar cross-section (RCS) values. The current trend in RCS reduction is concerned with multi-layered, wideband designs, which are intrinsically difficult to model because of the number of variables involved. The third chapter provides a specific design methodology for the case of gun fire-control systems: because this radar will track an incoming missile, the angle of incidence of the incident radiation will be zero, freeing the design from one variable and allowing the design of a single-layer metallic frequency selective surface to be effective in RCS reduction. A method based on the first order equivalent LC circuit is therefore presented, linking the physical dimensions of the filter to its expected performances. The resulting profile is generalized via bidimensional surface fitting, allowing broader design possibilities. Results of a realized prototype are also presented in the chapter.