Browsing by Author "O'Hagan, Daniel W"

Now showing 1 - 6 of 6
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    Open Access
    Development of a synchronisation and video conversion unit for Denel Overberg Test Range's tracking radar
    (2017) Uprety, Kushal; O'Hagan, Daniel W
    This dissertation discusses the re-development of a subsystem of the tracking radar (TR) at Denel Overberg Test Range (OTR), defined as the Synchronisation and Video Conversion Unit (SVCU). The SVCU performs the task of baseband video processing, generation of all synchronisation triggers, and timing within the TR. The report is based on the Research and Design (R&D) project conducted at Denel OTR and built on the previous study where an SVCU model was designed and tested in SystemVue. A comprehensive measurement and analysis of all functions was first conducted on all (identical) TRs of Denel OTR to verify against the limited literature that is available relating to the SVCU. Various anomalies were discovered between the design specification documents and measured values. Modifications made to functions in the SVCU as a result of development done on other subunits of the TR and not documented were also discovered. A comprehensively revised design specification and high-level description for the SVCU was then generated. A new SVCU architecture was specified to improve the current tasks performed by various discrete analogue and digital components, Single-Board Microcontroller and data bus interfaces using commercial off the shelf (COTS) hardware. A prototype was built on the National Instruments (NI) PCI eXtensions for Instrumentation Express (PXIe) platform, utilising high-speed ADCs and Field Programmable Gate Array (FPGA) modules. All functions of the SVCU were modelled and implemented on these modules using LabVIEW and LabVIEW FPGA software. Fractional Decimators were designed to meet the sample resolution requirement of the range gates (used for range and Doppler measurement). Custom functions were written to integrate samples to increase SNR and apply a correction for errors carried over during the I/Q demodulation. The jitter on the synchronisation pulse responsible for RF energy transmission (TX), the ADC sample clock, and triggers signals that need to travel over excessively long transmission lines used for calibration were found to be the most critical aspects of the SVCU. The rootsum- square of all the jitter on these synchronisation pulses was calculated to ensure that the specified measurement accuracy of the TR is satisfied. Based on these findings, the PXIe based SVCU is recommended for deployment. Further development of other subunits for the TR receiver on the current platform is recommended, and an outline for future work is provided.
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    Implementation of a low cost demonstrator riometer on a flexible FPGA backend: The first steps in adding a riometer mode to the digital SuperDARN radar at SANAE IV
    (2018) Dusterwald, Thomas; O'Hagan, Daniel W
    SuperDARN is an international network of 35 HF radars located near the poles of the Earth dedicated to determining the state of the ionosphere at high latitudes. One of the SuperDARN radars is located at South Africa's base in Antarctica (SANAE IV) and is administered by the South African National Space Association (SANSA). The radar at SANAE IV was recently upgraded to a fully digital transceiver, with the addition of a Field Programmable Gate Array (FPGA) at the core of this upgrade. FPGAs allow for easy hardware reconfiguration and high-performance computing. The aim of this project is to determine the feasibility of using the FPGA on board the radar at SANAE IV to implement a riometer mode to run simultaneously with its main mode of operation, adding a new tool to the radar's set of abilities without any investment in new hardware. The riometer function could easily be ported to other radars in the SuperDARN network, allowing for a significant increase in riometer coverage of the polar regions. As a first step towards achieving this goal, a demonstrator riometer is developed using the Red Pitaya FPGA platform as its backend, and tested at the University of Cape Town, at SANSA in Hermanus and at Fish Hoek. A riometer measures the opacity of the ionosphere with respect to cosmic radiation. Doing this over a wide band of frequencies results in a spectral riometer. This dissertation describes the design and implementation of both a single frequency and a spectral riometer, both implemented on the Red Pitaya, and the results of testing these implementations. Experimentation alongside a La Jolla 38MHz riometer revealed very similar performance for the low-cost demonstrator riometer. It is thereby shown that low cost HF riometry is possible and that it is feasible to implement a riometer on the radar at SANAE IV. However, an additional FPGA is required.
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    Integration and testing of a digital transceiver for a dual frequency, pulse-doppler radar
    (2016) Du Plessis, Dane; Inggs, Michael; O'Hagan, Daniel W
    This dissertation focuses on the development of a digital transceiver system for a dual-band, polarimetric radar, which is to form part of the NeXtRAD multistatic radar. NeXtRAD is being developed as an instrument for research into the behaviour of clutter and targets as observed by multistatic radars. The Pentek Cobalt model 71621 software defined radio interface was procured for use as the digital transceiver in the system. The goal was to develop the software needed to use this product as the digital transceiver in a prototype version of the NeXtRAD active node, and to ensure that it could be readily integrated with other subsystems in the final system. The active node is essentially a monostatic pulse-doppler radar. Laboratory tests of the transceiver showed that it was possible to generate and digitize pulsed waveforms at a 125 MHz intermediate frequency which is used by the existing receiver exciter in the system. After extensive laboratory testing and development, phase coherent waveform generation and multichannel digitization was achieved. A low transmit power version of the active node was constructed and tested at both operating frequencies. Equipment used in the testing and development of the digital transceiver included laboratory signal generators, spectrum analyzers and oscilloscopes. The digital transceiver was able to function at pulse repetition rates exceeding 2 kHz, with a single transmit channel and three receive channels active. The lowpowered monostatic prototype system was constructed to test the digital transceiver using a receiver exciter subsystem, RF amplifiers and antennas. This prototype radar was used to take measurements of targets at ranges below 300 m and successfully detected reflections from large structures. Cars and pedestrian traffic were detected by their doppler shifts at both L- and X-band frequencies. The detection of moving and stationary targets confirmed the suitability of the digital transceiver for use in the envisioned multistatic radar system.
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    Modelling and resolving of the ambiguous angle of arrival measurements of the SANAE IV SuperDARN Radar
    (2017) Barris, Tighe; O'Hagan, Daniel W
    The Super Dual Aural Radar Network (SuperDARN) forms a multinational collaboration consisting of over 30 HF radars used to monitor charged particle convections in the high latitudes of the ionosphere. This research is inspired by the antenna arrangement of one of these HF radars situated at the South African National Antarctic Expedition (SANAE) IV base. This radar consists of a steered 16-element primary array, and a second 4-element interferometer array. Phase wrapping is introduced into echoed returns due to the two arrays being separated by 100 m, several wavelengths of the carrier frequency. As a result, the radar system is only able to unambiguously determine the Angle of Arrival (AOA) for a given target provided it resides below 33ᵒ in elevation when observing along boresight. This dissertation models a subcomponent of this phenomenon and develops an entirely separate pulsed-Doppler radar system on an FPGA platform known as the Red Pitaya. Operating parameters are specifically chosen to be consistent with the SANAE IV radar. An antenna arrangement consisting of two receivers and a transmitter is constructed to replicate the AOA issue experienced by the SANAE radar. Instead of focusing on detecting targets in elevation, as done with the SuperDARN radars, targets are detected in azimuth. Three algorithms are developed to autonomously measure the AOA and to counteract the effects of 2π phase wrapping. The naïve measurement applies no corrections and is only able to detect targets at angles within ±17.10ᵒ of boresight. This is the theoretical maximum measurable AOA when operating at 17 MHz. A second algorithm involving a Standard Deviation (STDEV) search process is used to successfully measure angles up to ±70ᵒ for the same arrangement. It does this by varying the carrier frequency and using numerous received aliased AOAs to correct and expand for a true AOA. Empirical results yield an average Mean Square Error (MSE) of 0.29 between the true and measured target angles. A third algorithm involving the Chinese Remainder Theorem (CRT) was shown to work in theory (albeit only up to ±66ᵒ), but failed to perform in practice. Results presented in this dissertation indicate that the maximum measurable AOA is expanded by a factor of 4 by using the STDEV algorithm. It is postulated that the same result can be achieved using the actual SuperDARN radar. Theory relevant to generating the RF Linear Frequency Modulated (LFM) chirp and its use for transmitting, receiving and processing is covered. Topics of pulse compression, range resolution, environment modelling, reconstruction and matched filtering, coherent integration, sidelobe reduction and demodulation are detailed.
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    Software Infrastructure for NeXtRAD Development in Julia Programming Language
    (2016) Jonkers, Stephanie Cavale; O'Hagan, Daniel W
    This dissertation presents the implementation of signal processing infrastructure in Julia Programming Language. The aim is to aid sea clutter analysis using NetRAD and NeXtRAD data. Scripts written in Julia Programming Language and supporting documentation on how to navigate through compressed HDF5 files, apply pulse compression, pulse-Doppler processing and an adaptive LMS filter for interference suppression is presented. Both serial and multi-core pulse compression and pulse-Doppler processing functions are implemented. The assessment of the algorithm computation times highlights Julia's dependence on large amounts of RAM and slow data movement between worker processes. Multi-core pulse compression on 130 000 pulses each with 2 048 samples was not found to be faster than the serial implementation. Multi-core pulse-Doppler processing was able to achieve a speedup of 1:6 for a dataset with 102 400 pulses. Datasets larger than 102 400 pulses resulted in a memory bottleneck. The adaptive LMS filter was validated by applying an OS-CFAR detector to match filtered data before and after filtering. The filter was unable to improve the precision or recall for highly cluttered pulses, but was able to reduce the number of highly cluttered pulses.
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    X-band Doppler simulator for sport projectile radars
    (2018) Barsch, Binjamin; O'Hagan, Daniel W
    Systems engineering has always required that hardware is evaluated in its desired environment. However, this may not be feasible as the target or environment may be too complex or too costly to use at any given time. This is a common problem with evaluating Doppler radars as well, since the inherent property of a Doppler radar is to measure the radial velocity of objects in motion like aircraft or projectiles. A common solution to this problem is to perform a hardware- in-the-loop (HIL) simulation. This usually comprises of a device that does a real-time simulation of the environment or moving target. In the field of RF engineering, such a device is known as a repeater or a Doppler simulator. Depending on the application, these devices use either the digital radio frequency memory (DRFM) or direct digital synthesis (DDS) simulation method. Developing Doppler simulators as a diagnostic tool for sport Doppler radars is a growing need to evaluate and assess the performance of these radars. This dissertation will investigate the design and development of a Doppler simulator that can be used to simulate projectiles for sport Doppler radars. The scope of this dissertation was restricted to the sport of golf using continuous wave (CW) X-band Doppler radars. Raw data was measured by a Doppler radar to determine the velocity profiles of golf balls in flight. From these profiles, flight models were developed that could be simulated using a Doppler simulator. An Arduino Due microcontroller was used to implement the digital DDS method and to simulate these velocity profiles. This microcontroller was integrated into an existing Doppler simulator that lacked the capabilities to simulate a velocity profile. Results showed that the projectile based sport Doppler simulator was effective in simulating the modeled flight trajectories. A close comparison between the simulated and measured result were shown. For three different types of golf shots, the average error between the simulated and measured trajectories was -0.169 m/s while the standard deviation was 0.28 m/s. This dissertation also showed future possibilities in simulating a diverse range of projectiles and targets.