Alhuwaimel, Saad; (2018) Fully Polarimetric Slotted Waveguide Antenna Array. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Multistatic radar system provides a great number of advantages over monostatic radar systems via exploitation of geometrical diversity which gives the ability to view targets from multiple perspectives. These advantages include target signature enhancement, improved detection, higher immunity against countermeasures and provide more information about targets and hence enhance targets classification. Furthermore, the passive receive-only nodes are more compact, hence lighter weight, and can be mounted on UAV which leads to a great advantage to surveillance systems and military applications. Over the last two decades, University College London and the University of Cape Town have collaborated to develop multistatic radar systems. This collaboration resulted in developing an S-band system (NetRAD). Recently, a new version of the system (NeXtRAD) that operates in X and L bands has been developed. The NeXtRAD system has two channels at X-band which allows for receiving fully polarimetric data from clutter and targets utilising dual-polarised antenna. The first addressed task of this work was to investigate all possible antenna candidates to be used for the NeXtRAD system. Resonant SWGAA was chosen among the antenna options as it fit best all desired criteria and due to its relative design simplicity, high power-handling capabilities and cost-effective fabrication. The SWGAA can be designed to be a dual-polarised antenna. The procedures for designing a low sidelobe level (SLL) S-band SWGAA are demonstrated in this work. The azimuth beamwidth of a SWGAA is controlled by the number of slots carved in a waveguide. Eight slots distributed around the centre-line of waveguide broad wall found to meet the desired beamwidth. Four SWGAAs were designed and fabricated. The anechoic chamber measurements of each SWGAA showed excellent agreement with the simulation results. A single element SWGAA has a fan elevation beamwidth. This beamwidth has to be narrowed to achieve the desired width. Stacking identically designed SWGAAs was found to be an effective and simple method to narrow the antenna elevation beamwidth. The four SWGAAs were stacked on top of each other. The mitigation of mutual coupling between stacked SWGAAs was investigated. A cost-effective method of inserting dielectric sheets between stacked SWGAAs helped in mitigating the mutual coupling and assist in arriving at the desired antenna performance. The stacked SWGAAs shows a very good performance with very low SLL and high polarisation purity (low cross-polarisation level). The stacked SWGAAs antenna performance was validated in field experiments and compared to similar characteristics antenna. The SWGAA shows better performance compared to the other antenna. A new simple and efficient design of a dual-polarised SWGAA by having two similar set of stacked waveguides with one set rotated by 90ᵒ relative to the other one was proposed. Two designs with two different elevation beamwidths were simulated. Both designs showed excellent performance that met all the desired criteria. The same designs and tests procedures were followed in designing and testing the X-band SWGAA and simulating dual-polarised antennas. No field experiments were performed using this antenna as the NeXtRAD system is based at UCT and no access to any other X-band radar system at UCL.

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