Analysis and Optimization of Installed Antenna Performance
Time: Mon 2020-03-09 13.00
Subject area: Electrical Engineering
Doctoral student: Henrik Frid , Skolan för elektroteknik och datavetenskap (EECS)
Opponent: Professor Hugh Griffiths, University College London
Supervisor: B. Lars G. Jonsson, Elektroteknisk teori och konstruktion
This Ph.D. thesis consists of six papers, which are labeled with roman numerals. Papers I-III have already been presented in a licentiate thesis published in2017, and this Ph.D. thesis therefore focuses on Papers IV-VI. All six papersare within the scope of microwave and antenna engineering, with applications to radar, electronic warfare (EW), radio astronomy or communications.
The common theme for Papers IV-VI is installed antenna performance (IAP). These papers present three methods for solving three problems related to IAP, by using information available in the installed far-ﬁeld data. In these papers, we address the main challenges within the scope of IAP, i.e. antenna placement, electromagnetic compatibility (EMC), estimation of installed system performance (particularly direction-of-arrival (DoA) estimation accuracy)and optimization methods to compensate for or minimize installation eﬀects. The presented methods make no simplifying assumptions regarding the antennas or their installation, and instead rely on using the installed far-ﬁeld data, which is obtained through computational electromagnetics. These methods are therefore valid for generic array antennas. The presented methods are useful for antenna placement studies, i.e. as input for the decision on antenna placement on a platform such as an aircraft, ship, satellite or car.
Paper IV considers the problem of antenna placement with respect to EMC. A platform, such as an aircraft, ship, satellite, or car, may have a large number of radio-frequency (RF) systems installed onboard. Since some systems transmit a high RF power, while other systems aim to receive weak RF signals, there is a signiﬁcant risk for unwanted electromagnetic interference (EMI) due to an insuﬃcient isolation between the antennas associated with each RF system. This paper presents a method for estimating the isolation between antennas installed on the same platform, in order to determine therisk for EMI as a function of antenna placement. Finally, a numerical case-study is presented, considering two monopole antennas installed on a small aircraft under line-of-sight conditions. Results are also presented for other installation conﬁgurations, where the antennas are not within line-of-sight.
Paper V considers antenna placement and radome design with respect to DoA estimation accuracy. Firstly, we deﬁne the term "installation error" applied to DoA estimation. A method for determining the DoA estimation accuracy for a speciﬁc installation is thereafter presented. The paper ends with a numerical case-study for an array antenna installed behind a single-shell radome in the tail of a realistic full-scale model of a ﬁghter aircraft.
Paper VI presents a method to compensate for radome eﬀects on radiation patterns for array antennas. A convex optimization approach is used to minimize the side-lobe level, while taking the radome eﬀects and mutual coupling into account. The paper ends with a numerical case-study for amonopulse-array installed behind a single-shell radome.