Browsing by Author "Downing, Barry"

Now showing 1 - 4 of 4
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    Design and implementation of a dual polarised L-band parabolic dish antenna for NeXtRAD
    (2016) Paine, Stephen Thomas; O'Hagan, Daniel; Downing, Barry
    Research into multi-static, multi-band networked radar has led to the development of the NeXtRAD radar system. This dissertation will investigate the design and implementation of a dual polarised L-Band prime focus dish antenna with a centre frequency of 1.3 GHz and a HPBW of 10° in the azimuth plane. The antenna is required to handle a peak power of 1.5 kW over a 50 MHz bandwidth and be able to withstand environmental factors such as wind while mounted on a tripod. This dissertation forms part of the larger NeXtRAD project and as such, the antenna design requirements have been set based on the wider system specifications. Previous investigations into the feasibility of various antenna designs have concluded that a prime focus parabolic dish antenna would be the most appropriate to meet the design requirements. The dissertation details the design and manufacturing process followed. All antenna parameters have been simulated using a combination of FEKO v7 and CST 2014 to compare and verify the designs and simulations. Due to manufacturing limitations, the optimal antenna design could not be manufactured and, as a result, compromises had to be made in order for an antenna prototype to be manufactured and tested. These tests include, amongst others, characterisation of the return loss, cross polarisation, gain, beamwidth and beam pattern of the antenna in both planes of polarisation. These results have been recorded, analysed and compared to those found through simulations.
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    Design and Implementation of an RF front end for the NeXtRAD radar system
    (2017) Stevens, Adrian Dale; Geschke, Riana; Downing, Barry
    This dissertation presents the design of the RF front end for use on the NeXtRAD radar system. The system is intended for research purposes to investigate potential target detection benefits to be derived from a multistatic, dual-band (X- and L-band), polarimetric radar architecture, particularly within dense clutter environments such as the maritime environment. By examining the high-level system requirements and objectives, requirement specifications for the RF front end were derived and a suitable architecture, making use of commercial off-the-shelf components, proposed. This architecture was modified in order to meet cost constraints - subsequently offering reduced levels of functionality but suitable for an initial build. Using this modified RF front end architecture, design verification and system analysis was conducted, both analytically and with the aid of SystemVue, in order to predict both the front end and overall radar detection performance. Once the front end design was found to be satisfactory, it was built and tested in a laboratory environment. Test results revealed a general improvement in performance when compared with the design predictions, yielding peak transmitter power levels in excess of 61dBm at L-band, and 54dBm at X-band. Some non-conformances were also identified, but these were as a result of component problems and not system design. Since the front end could not yet be integrated into the radar, performance modelling was repeated using the final lab test results. This indicated a negligible improvement in receiver single-pulse signal-to-noise ratio, but confirmed that the system performed as predicted. Based on the lab test results, it was concluded that the 'as-built' front end design closely matched the design goals and would be suitable for eventual integration into the first revision of the NeXtRAD system. It was, however, recommended that a concerted effort be made to secure funding to implement the original front end architecture in order to achieve the full system functionality originally desired.
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    Polar frequency discriminators
    (1986) Rachman, David Malcolm; Downing, Barry
    This dissertation makes a study of frequency discriminators and their role in instantaneous frequency measuring (IFM) signal acquisition receivers. Frequency discriminators are the major building blocks of IFM. They are required to measure frequency accurately over very broad bandwidths and to have near unity probabilities of pulse intercept. The major difficulties of the most commonly reported version are identified as a lack of component symmetry and a need to cross over two transmission lines while maintaining isolation. The accuracy due to lack of symmetry shows up analytically. effect on TOUCHSTONE, a micro-computer analysis package, is demonstrated as an excellent analysis tool while alternatives are also suggested. Variations of the standard discriminator are discussed. These are intended to improve performance due to lack of symmetry. None completely solve the cross over problem. A new type of discriminator requiring fewer components is introduced. It requires no cross over and exhibits greater symmetry. Analysis indicates that it performs better than the standard version. Two prototypes show the methods to be reliable and confirm the promise of the new version.
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    The design of a 94 GHz high resolution coherent radar
    (1988) Celliers, Abraham Francois; Downing, Barry
    This thesis describes the design and performance of a 94 GHz short pulse, low duty cycle, high resolution coherent injection locked radar system for sensor applications, with the specific use as an early warning radar ,against high voltage transmission lines. The recent development of solid-state components for frequencies around 94 GHz has made it possible to design coherent millimetre-wave radar systems. Key components of such systems are high power pulsed silicon Impact oscillators, CW Impact oscillators, second harmonic Gunn oscillators, filters, circulators, isolators, couplers, and antennas. Elementary system specifications are derived for the delivery vehicle and the millimetre-wave sensor. Each of the separate components of the system were designed, built, and tested. Measurements were taken with the sensor and are presented. Specific attention is given to the measurement of intra-pulse phase ripple, additive noise, injection locking and coherency. The above-mentioned parameters are critical in the design of a coherent sensor and special care should be given to the various components in the design stage. The sensor is not built into a carrier system yet but was built up as a laboratory model and measurements were taken from the laboratory to various objects and distances outside the laboratory. There is only one article in literature [1] which described a 66 GHz collision warning sensor for helicopters. The system is a noncoherent pulsed radar with the following specifications: