Browsing by Author "O'Hagan, Daniel"

Now showing 1 - 11 of 11
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    Open Access
    Automatic generation of a floor plan from a 3D scanned model: Making the Analogue World Digital
    (2018) Wilson, Bradlee Kenneth; Winberg, Simon; O'Hagan, Daniel
    The processing of three-dimensional (3D) room models is an area of research undertaken by many academics and hobbyists due to multiple uses derived from the information obtained - such as the generation of a floor plan; an example of bridging the real and digital world. A floor plan is required when an existing room, floor, or building requires alteration. By having the floor plan in the digital domain it allows the user to alter the room via simulation and render the environment in a life-like manner to determine if the alterations will suffice. This is done using Computer Aided Design Software (CAD). Designing a new room or building would be done using CAD software. However, not all building's digital files are readily available or exist - making the creation of a floor plan necessary. The floor plan can created up by a person on pen and paper, or with using software tools and sensors. Commercial systems exist for this task but there are no automated, open-source systems that can do the same. Current research tends to focus on the processing algorithms and not the sensors or methods for capturing the environment. This dissertation deals with testing and evaluating off-the-shelf (OTS) sensors and the processing of 3D modelled rooms captured with one of these sensors. The tests performed on the OTS sensors determine the overall accuracy of the sensors for 3D room modelling. The rationale for designing and conducting these tests is to provide the community with suggested practical tests to assist in selecting an OTS sensor for 3D room modelling. The 3D room models are captured using an opensource application and are imported into custom software. The 3D models undergo pre-processing algorithms producing 2D results, which were further processed to determine the walls of rooms. The dimension information about these features are used to create a 2D floor plan. 3D modelled environments are inherently noisy, requiring efficient pre-processing to remove the noise without hampering processing performance of the 3D model. One of the largest contributors to noise and accuracy is the sensor. Selecting the appropriate sensor can mitigate the need for complex pre-processing algorithms and will improve overall processing time. The project was able to extract dimension information within an acceptable error. The tests that were designed and used for sensor testing were able to determine which sensor was the better choice for 3D room modelling. The optimal sensor was found to be Microsoft's Kinect1 . Tests were performed in which the Microsoft Kinect was required to map a room. The results show that dimensional information about the given scene could be successfully extracted with an average error of 4.60 %.
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    Open Access
    Beamforming and scan pattern performance evaluation of rotating maritime multi-beam phased array surveillance radar
    (2022) van Heerden, Lourens; O'Hagan, Daniel; Schonken, Francois
    Modern naval ships face a wide spectrum of threats, from fast-moving sea-skimming missiles to slow-moving unmanned vehicles and boats. The rotating phased array naval surveillance radar provides 360° azimuth coverage at large elevation angles for early warning to initiate the appropriate action and countermeasures timeously. This dissertation aimed to provide a simulation model to test and evaluate the effect of different beamforming and scan patterns on the detection performance of different possible targets in the maritime environment per antenna rotation. MATLAB, with various Phased Array Toolbox objects, was used as the platform to create the simulation model. A wide variety of variables were adjusted to test the effect on detection performance per rotation against a specified target. It distinguished between air (fast) targets with a medium Pulse repetition frequency (PRF) waveform and surface (slow and low) targets with a low PRF waveform. Coherent and noncoherent (surface only) processing algorithms were used. Complex clutter data sets from the CSIR Fynmeet sea clutter measurement trial were adapted according to the Georgia Institute of Technology (GIT) model, clutter area model and radar range equation to be inserted into each pulse. The output was a detection table for the air and surface channel for the evaluated sector per rotation. In order to determine detection performance, multiple rotations and target scans with clutter data offsets were required. The simulation model provided insight into the effect of beamforming and scan patterns on the detection performance of both fast and slow-moving targets. It was found that with coherent fast target air surveillance and sufficient clutter suppression, a fast-moving target could be detected with a detection probability of 1 and a false alarm probability of 0. This could be achieved with a single or dual-axis stacked beam. In a single axis stacked beam, only non-coherent integration of low quantity, low PRF pulse bursts could be used for the surface channel as time resources were limited to a single beamwidth. In this case, cell averaging constant false alarm rate (CA-CFAR) detection provided better results in a homogeneous and small target signal-to-clutter ratio (SCR) environment (as was the case at far ranges). The detection probability was 1 and false alarm probability was 0.03. In a spiky and large target SCR environment (as was the case at near ranges), constant threshold detection performed better. The detection probability was 1 and false alarm probability was 0. High Doppler resolution coherent integration of a large number of low PRF pulses could be used in a dual axis beam for the surface channel. This type of detection provided results comparable to non-coherent detection. The detection probability was 1 and false alarm probability was 0.02 at far ranges, and 1 and 0.06 respectively at near ranges. When the target's Doppler frequency was within the clutter's Doppler spectrum, the target was not detectable.
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    Open Access
    Design and feasibility evaluation of low-cost 3D printing of Horn Antennas
    (2019) Gao, Ming; O'Hagan, Daniel; Geschke, Riana
    This dissertation investigates advances in additive manufacturing (AM) technology to determine the feasibility of low-cost 3D printing of horn antennas. Relevant antenna theory and current 3D printing technologies are reviewed and a literature review is conducted looking specifically at microwave and RF devices that have been fabricated using 3D printing technologies. The literature indicates that the fabrication of antennas using AM and metallisation techniques is realisable. One of the objectives of this study has been to design, fabricate and test the performance of lowcost 3D printed antennas to determine their feasibility. To achieve this, a commercial X-band pyramidal horn has been replicated using the microwave simulation package FEKO. The X-band horn has been fabricated using an FDM-based 3D printer and metallised using conductive paint. Ku-band pyramidal and conical horns have also been designed and 3D printed using the same method and have been metallised using both conductive paint and electroplating. The fabricated horns have been measured and tested in an anechoic chamber with the measured results analysed. The fabricated X-band pyramidal horn achieved a gain of 9.2 dBi with an input reflection coefficient of −11.9 dB at a centre frequency of 10 GHz. This is in agreement with the measured gain and reflection coefficient of the X-band commercial horn. The Ku-band pyramidal horns that have been metallised using conductive paint and copper plating achieved gains of 17.5 dBi and 17.7 dBi respectively, measured at a centre frequency of 15 GHz. The input reflection coefficients for the painted Ku-band pyramidal horns are measured as −24.2 dB while the copper plated horns are measured as −23.3 dB. The second set of Ku-band conical horn antennas designed have also been metallised using conductive paint and copper plating. These two antennas achieved gains of 12.0 dBi and 16.6 dBi respectively at a centre frequency of 15 GHz. The input reflection coefficient for the painted Kuband conical horn is −15.2 dB while the plated version has a reflection coefficient of −18.3 dB. The total cost of fabricating and testing each antenna amounted to approximately ZAR 475 per antenna, an order of magnitude lower than the price of a traditional cast or milled antenna. The method of fabrication demonstrated in this report is relatively fast and inexpensive while producing favourable results. As such, this method is highly suited for rapid prototyping and development of more advanced antenna designs.
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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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    Discrete Wavelet Methods for Interference Mitigation: An Application To Radio Astronomy
    (2019) Mesarcik, Michael; O'Hagan, Daniel; Cavalier, Paul
    The field of wavelets concerns the analysis and alteration of signals at various resolutions. This is achieved through the use of analysis functions which are referred to as wavelets. A wavelet is a signal defined for some brief period of time that contains oscillatory characteristics. Generally, wavelets are intentionally designed to posses particular qualities relevant to a particular signal processing application. This research project makes use of wavelets to mitigate interference, and documents how wavelets are effective in the suppression of Radio Frequency Interference (RFI) in the context of radio astronomy. This study begins with the design of a library of smooth orthogonal wavelets well suited to interference suppression. This is achieved through the use of a multi-parameter optimization applied to a trigonometric parameterization of wavelet filters used for the implementation of the Discrete Wavelet Transform (DWT). This is followed by the design of a simplified wavelet interference suppression system, from which measures of performance and suitability are considered. It is shown that optimal performance metrics for the suppression system are that of Shannon’s entropy, Root Mean Square Error (RMSE) and normality testing using the Lilliefors test. From the application of these heuristics, the optimal thresholding mechanism was found to be the universal adaptive threshold and entropy based measures were found to be optimal for matching wavelets to interference. This in turn resulted in the implementation of the wavelet suppression system, which consisted of a bank of matched filters used to determine which interference source is present in a sampled time domain vector. From this, the astronomy based application was documented and results were obtained. It is shown that the wavelet based interference suppression system outperforms existing flagging techniques. This is achieved by considering measures of the number of sources within a radio-image of the Messier 83 (M83) galaxy and the power of the main source in the image. It is shown that designed system results in an increase of 27% in the number of sources in the recovered radio image and a 1.9% loss of power of the main source.
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    Electronic countermeasures applied to passive radar
    (2019) Paine, Stephen Thomas; O'Hagan, Daniel
    Passive Radar (PR) is a form of bistatic radar that utilises existing transmitter infrastructure such as FM radio, digital audio and video broadcasts (DAB and DVB-T/T2), cellular base station transmitters, and satellite-borne illuminators like DVB-S instead of a dedicated radar transmitter. Extensive research into PR has been performed over the last two decades across various industries with the technology maturing to a point where it is becoming commercially viable. Nevertheless, despite the abundance of PR literature, there is a scarcity of open literature pertaining to electronic countermeasures (ECM) applied to PR. This research makes the novel contribution of a comprehensive exploration and validation of various ECM techniques and their effectiveness when applied to PR. Extensive research has been conducted to assess the inherent properties of the lluminators of Opportunity to identify their possible weaknesses for the purpose of applying targeted ECM. Similarly, potential jamming signals have also been researched to evaluate their effectiveness as bespoke ECM signals. Whilst different types of PR exist, this thesis focuses specifically on ECM applied to FM radio and DVB-T2 based PR. The results show noise jamming to be effective against FM radio based PR where jamming can be achieved with relatively low jamming power. A waveform study is performed to determine the optimal jamming waveform for an FM radio based PR. The importance of an effective direct signal interference (DSI) canceller is also shown as a means of suppressing the jamming signal. A basic overview of counter-ECM (ECCM) is discussed to counter potential jamming of FM based PR. The two main processing techniques for DVB-T2 based PR, mismatched and inverse filtering, have been investigated and their performance in the presence of jamming evaluated. The deterministic components of the DVB-T2 waveform are shown to be an effective form of attack for both mismatched filtering and inverse filtering techniques. Basic ECCM is also presented to counter potential pilot attacks on DVB-T2 based PR. Using measured data from a PR demonstrator, the application and effectiveness of each jamming technique is clearly demonstrated, evaluated and quantified.
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    High frequency surface wave radar demonstrator
    (2018) Burger, Johann; O'Hagan, Daniel; Wilkinson, Andrew
    High Frequency Surface Wave Radar (HFSWR) is used around the globe for the mapping of sea currents and coastal monitoring of the Exclusive Economic Zone. Decision to build an HF radar at the University of Cape Town (UCT) was made by Daniel O’Hagan and Andrew Wilkinson in February 2015 immediately after seeing a demonstration of the CODAR system at IMT. Their intention was subsequently discussed at several meetings, including a South African Radar Interest Group (SARIG) meeting and one at IMT in order to gauge interest and raise funding. There was both interest (mainly for ocean current monitoring) and scepticism (expressed by CSIR and SARIG members) of the value of HF radar for ship monitoring. This reports the design, construction, test, and evaluation of the UCT HFSWR demonstrator. A modular approach was taken in its design and construction making it easy to replicate and upscale. A pillar of this work is to prove the feasibility of a software defined radar (SDR) based HF radar demonstrator. Every part of the demonstrator was designed and constructed from scratch as UCT had no prior HF activities, and therefore no legacy antennas or components to utilise. A low-cost RF frontend follows the HF antennas, which were also designed for this project. Combined with an SDR platforn known as the Red Pitaya (RP), a complete HF radar demonstrator was assembled and trials were conducted at the UCT rugby field and at the IMT facilities in Simon’s Town. A preliminary assessment of the results reveal the effects of Bragg resonance scatter and detection of two stationary targets (mountains) distinguishable by both range and azimuth. This assessment of the results indicates that the demonstrator is operational.
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    Implementation of a DVB-T2 passive coherent locator demonstrator
    (2019) Malape, Micheal Thatohatsi; O'Hagan, Daniel; Schonken, Willem
    Passive Coherent Locator (PCL) radar’s have seen extensive research in the past decade. PCL radars utilize illuminators of opportunity (IOO) as transmitters to perform target detection. Particular interests in FM (analogue) and DVB-T/T2, DAB (digital) radio frequency signals has seen significant focus as possible illuminators for radar processing. The University of Cape Town (UCT) , in particular, has extensive history on passive radar research including the implementation of a full narrowband FM PCL radar demonstrator. This dissertation details the design and implementation of a DVB-T2 Passive Coherent Locator radar demonstrator isolating a single DVB-T2 channel. This includes the design, construction, testing and evaluation of the full PCL radar system. System planning was implemented detailing the possible IOOs available in the Cape Town area. This was followed by signal propagation simulations to determine the effects the environment would have on the transmitted wave utilising Advanced Refractive Effects Prediction System (AREPS) model. A front-end design was simulated and implemented utilizing commercial-of-the-shelf (COTS) hardware including the National Instruments Ettus N210 software defined Radio (SDR) based on the system planning results. A processing chain for DVB-T2 based PCL radar was then investigated to determine the most optimal processing chain structure, with the mismatched filtering technique being proposed as an ideal choice for DVB-T2 PCL radar. The proposed processing chain was implemented and tested on both the Ettus N210 front-end as well as a commercial system. The full radar demonstrator was then tested by observing the air traffic surrounding the Cape Town International airport resulting in successful detections of aircraft in the surveyed environment.
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    On particle filters in radar target tracking
    (2016) Bauermeister, Etienne F; O'Hagan, Daniel
    The dissertation focused on the research, implementation, and evaluation of particle filters for radar target track filtering of a maneuvering target, through quantitative simulations and analysis thereof. Target track filtering, also called target track smoothing, aims to minimize the error between a radar target's predicted and actual position. From the literature it had been suggested that particle filters were more suitable for filtering in non-linear/non-Gaussian systems. Furthermore, it had been determined that particle filters were a relatively newer field of research relating to radar target track filtering for non-linear, non-Gaussian maneuvering target tracking problems, compared to the more traditional and widely known and implemented approaches and techniques. The objectives of the research project had been achieved through the development of a software radar target tracking filter simulator, which implemented a sequential importance re-sampling particle filter algorithm and suitable target and noise models. This particular particle filter had been identified from a review of the theory of particle filters. The theory of the more conventional tracking filters used in radar applications had also been reviewed and discussed. The performance of the sequential importance re-sampling particle filter for radar target track filtering had been evaluated through quantitative simulations and analysis thereof, using predefined metrics identified from the literature. These metrics had been the root mean squared error metric for accuracy, and the normalized processing time metric for computational complexity. It had been shown that the sequential importance re-sampling particle filter achieved improved accuracy performance in the track filtering of a maneuvering radar target in a non-Gaussian (Laplacian) noise environment, compared to a Gaussian noise environment. It had also been shown that the accuracy performance of the sequential importance re-sampling particle filter is a function of the number of particles used in the sequential importance re-sampling particle filter algorithm. The sequential importance re-sampling particle filter had also been compared to two conventional tracking filters, namely the alpha-beta filter and the Singer-Kalman filter, and had better accuracy performance in both cases. The normalized processing time of the sequential importance re-sampling particle filter had been shown to be a function of the number of particles used in the sequential importance re-sampling particle filter algorithm. The normalized processing time of the sequential importance re-sampling particle filter had been shown to be higher than that of both the alpha-beta filter and the Singer-Kalman filter. Analysis of the posterior Cramér-Rao lower bound of the sequential importance re-sampling particle filter had also been conducted and presented in the dissertation.
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    Self-Interference Cancellation for Simultaneous Transmit and Receive (STAR) Applications
    (2019) Parker, Asif Ahmed; Schonken, Francois; O'Hagan, Daniel
    Co-channel interference between transmit and receive antennas means that simultaneous transmission and reception (STAR) of signals on the same frequency is an engineering challenge when co-locating the transmit and receive channels. Due to advancements in Radio Frequency (RF) receiver and antenna hardware, as well as electromagnetic computation software, this technology is becoming more and more realisable, with applications in the fields of radar and communications. For a STAR system to be effective, high isolation (in excess of 90 dB) between transmit and receive channels is required to avoid self-interference. A lack of isolation will result in a significant reduction in the receiver sensitivity and dynamic range, reducing its ability to adequately detect incoming signals. This study involves the design and analysis of a STAR demonstrator where the theoretical and practical viability of such a system is evaluated. High isolation is achieved through the use of a combination of passive suppression, as well as analogue and digital cancellation techniques. The design consists of three cancellation layers: passive suppression, which uses a transmit antenna array to increase the transmit-receive antenna isolation through null placement; analogue cancellation, which aims to reduce self-interference by subtracting a copy of the estimated interference signal from the received signal; and digital cancellation, which uses adaptive filtering in the digital domain to further suppress residual self-interference. The demonstrator is tested in a typical real-world environment to characterise the performance of the system. The measured isolation between transmit and receive antennas is 29.4 dB. Passive suppression increases this isolation to 51.5 dB when using a four element linear transmit array. Analogue cancellation provides up to 30 dB of additional isolation, with digital cancellation providing a further 20 dB of suppression. Together, as an integrated system, the demonstrator is capable of providing a combined 101.5 dB of self-interference suppression. This clearly demonstrates that a STAR system is viable through the use of a multi-layer cancellation scheme comprising of passive suppression, analogue cancellation and digital cancellation techniques.
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    Software packages performance evaluation of basic radar signal processing techniques
    (2019) Frantz, Xavier; O'Hagan, Daniel
    This dissertation presents a radar signal processing infrastructure implemented on scripting language platforms. The main goal is to determine if any open source scripted packages are appropriate for radar signal processing and if it is worthwhile purchasing the more expensive MATLAB, commonly used in industry. Some of the most common radar signal processing techniques were considered, such as pulse compression, Doppler processing and adaptive filtering for interference suppression. The scripting languages investigated were the proprietary MATLAB, as well as open source alternatives such as Octave, Scilab, Python and Julia. While the experiments were conducted, it was decided that the implementations should have algorithmic fairness across the various software packages. The first experiment was loop based pulse compression and Doppler processing algorithms, where Julia and Python outperformed the rest. A further analysis was completed by using vectors to index matrices instead of loops, where possible. This saw a significant improvement in all of the languages for Doppler processing implementations. Although Julia performed extremely well in terms of speed, it utilized the most memory for the processing techniques. This was due to its garbage collector not automatically clearing the memory heap when required. The adaptive LMS (least mean squares) filter designs were a different form of analysis, as a vector of data was required instead of a matrix of data. When processing a vector or one dimensional array of data, Julia outperformed the rest of the software packages significantly, approximately a 10 times speed improvement. The experiments indicated that Python performed satisfactorily in terms of speed and memory utilization. Physical RAM of computer systems is, however, constantly improving, which will mitigate the memory issue for Julia. Overall, Julia is the best open source software package to use, as its syntax is similar to MATLAB compared with Python, and it is improving rapidly as Julia developers are constantly updating it. Other disadvantage of Python is that the mathematical signal processing is an add-on realized by modules such as NumPy.