Active target location using crossed-dipole based circular array FMCW radar

• Main Author: Halai, S.
• Published: University College London (University of London) 2014
• Subjects: 621.3
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.634649

Active target location systems capable of measuring both range and bearing have niche applications, including maritime navigation where a seafaring vessel is manoeuvring in the vicinity of a harbour or an oil rig. Such systems can also be used to determine the location of other vessels for vessel-to-vessel personnel or material transfer. The usual approach is to combine FMCW radar with a mechanically or electrically steered beam, establishing both range and bearing to a target, respectively. The radar system described in this thesis is an innovative alternative approach, one that combines FMCW radar with a crossed-dipole antenna, which conveniently functions as a circular array, thereby simultaneously determining the range and bearing of an active target. By using phase mode excitation, neither mechanical nor electrical beam steering is required to locate the active target, as the receive antenna is able to monitor 360 in azimuth continually. However, due to the use of +1st and -1st order phase modes, the radar can only operate in an 180 sector unambiguously. The usual inherent problems with circular arrays being aected by multipath are also easily mitigated by the range resolution of the radar. This thesis describes in detail the development of a 2.44 GHz crossed-dipole antenna structure and its associated feed network. It also describes the first prototypes that led to its current form and goes on to discuss in detail the design and construction of the radar system and frequency shifted active target. Frequency shifting was implemented within the target to overcome the increased clutter power due to the omnidirectional receive antenna. However, firstly this thesis lays the foundation of radar theory, active targets, phase modes and basic antenna theory. Some of the literature associated with radars currently used in this type of scenario is also discussed. Appropriate analysis, modelling and experimental validation is conducted to assess system performance in relation to the predicted behaviour. The radar system was then tested in an open field, with the active target detected to a range of 125 m.