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Time-Offset Fractional-N PLLs for Heterodyne FMCW SAR
This text contains an investigation into the use of time-offset fractional-N phase locked loops (PLLs) for heterodyne frequency-modulated continuous-wave (FMCW) synthetic aperture radar (SAR) and the impact of spurii on such a system. Heterodyne receiver architectures avoid phenomena which limit the...
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| Format: | Thesis |
| Language: | English |
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Department of Electrical Engineering
2021
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| _version_ | 1867614437620318208 |
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| access_status_str | Open Access |
| author | Jordan, Darryn Anton |
| author2 | Abdul, Gaffar Mohammed Yunus |
| author_browse | Abdul, Gaffar Mohammed Yunus Jordan, Darryn Anton |
| author_facet | Abdul, Gaffar Mohammed Yunus Jordan, Darryn Anton |
| author_sort | Jordan, Darryn Anton |
| collection | Thesis |
| description | This text contains an investigation into the use of time-offset fractional-N phase locked loops (PLLs) for heterodyne frequency-modulated continuous-wave (FMCW) synthetic aperture radar (SAR) and the impact of spurii on such a system. Heterodyne receiver architectures avoid phenomena which limit the sensitivity of their homodyne counterparts, and enable certain inter-antenna feed-through suppression techniques. Despite these advantages, homodyne receivers are more prevalent owing to advantages in size, weight and cost. Designed to address this dilemma, the miloSAR is believed to be the only heterodyne FMCW SAR to employ a pair of time-offset fractional-N PLLs for waveform synthesis to enable low-cost heterodyning and simplify filter-based feed-through suppression. This system architecture is revealed to be susceptible to swept-offset spurii termed spur chirps which hinder the sensor's performance. While integer boundary spurs and phase detector harmonics infamously plague fractional-N PLLs, their resultant spur-chirps have not seen analysis in the context of FMCW SAR. Simulations and measurements reveal that these spurii significantly degrade SAR image quality in terms of peak sidelobe ratio, structural similarity index measure and root mean square error. To combat this, several suppression techniques were assessed, namely: time domain zeroing, PLL loop bandwidth reduction, and a novel method termed range-Doppler spur masking. A subset of these suppression techniques were applied to measured SAR data sets, including car-borne data measured in Iowa, USA and airborne data captured in Oudtshoorn, South Africa. These results show that the impact of spur chirps can be effectively quelled, meaning that time-offset fractional-N PLLs offer an attractive, low-cost approach to the implementation of heterodyne FMCW SAR. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/33820 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:52:02.108Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2021 |
| publishDateRange | 2021 |
| publishDateSort | 2021 |
| publisher | Department of Electrical Engineering |
| publisherStr | Department of Electrical Engineering |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/33820 Time-Offset Fractional-N PLLs for Heterodyne FMCW SAR Jordan, Darryn Anton Abdul, Gaffar Mohammed Yunus Inggs, Michael Raymond Electrical Engineering This text contains an investigation into the use of time-offset fractional-N phase locked loops (PLLs) for heterodyne frequency-modulated continuous-wave (FMCW) synthetic aperture radar (SAR) and the impact of spurii on such a system. Heterodyne receiver architectures avoid phenomena which limit the sensitivity of their homodyne counterparts, and enable certain inter-antenna feed-through suppression techniques. Despite these advantages, homodyne receivers are more prevalent owing to advantages in size, weight and cost. Designed to address this dilemma, the miloSAR is believed to be the only heterodyne FMCW SAR to employ a pair of time-offset fractional-N PLLs for waveform synthesis to enable low-cost heterodyning and simplify filter-based feed-through suppression. This system architecture is revealed to be susceptible to swept-offset spurii termed spur chirps which hinder the sensor's performance. While integer boundary spurs and phase detector harmonics infamously plague fractional-N PLLs, their resultant spur-chirps have not seen analysis in the context of FMCW SAR. Simulations and measurements reveal that these spurii significantly degrade SAR image quality in terms of peak sidelobe ratio, structural similarity index measure and root mean square error. To combat this, several suppression techniques were assessed, namely: time domain zeroing, PLL loop bandwidth reduction, and a novel method termed range-Doppler spur masking. A subset of these suppression techniques were applied to measured SAR data sets, including car-borne data measured in Iowa, USA and airborne data captured in Oudtshoorn, South Africa. These results show that the impact of spur chirps can be effectively quelled, meaning that time-offset fractional-N PLLs offer an attractive, low-cost approach to the implementation of heterodyne FMCW SAR. 2021-08-24T01:46:56Z 2021-08-24T01:46:56Z 2021 2021-08-24T00:04:18Z Doctoral Thesis Doctoral PhD http://hdl.handle.net/11427/33820 eng application/pdf Department of Electrical Engineering Faculty of Engineering and the Built Environment |
| spellingShingle | Electrical Engineering Jordan, Darryn Anton Time-Offset Fractional-N PLLs for Heterodyne FMCW SAR |
| thesis_degree_str | Doctoral |
| title | Time-Offset Fractional-N PLLs for Heterodyne FMCW SAR |
| title_full | Time-Offset Fractional-N PLLs for Heterodyne FMCW SAR |
| title_fullStr | Time-Offset Fractional-N PLLs for Heterodyne FMCW SAR |
| title_full_unstemmed | Time-Offset Fractional-N PLLs for Heterodyne FMCW SAR |
| title_short | Time-Offset Fractional-N PLLs for Heterodyne FMCW SAR |
| title_sort | time offset fractional n plls for heterodyne fmcw sar |
| topic | Electrical Engineering |
| url | http://hdl.handle.net/11427/33820 |
| work_keys_str_mv | AT jordandarrynanton timeoffsetfractionalnpllsforheterodynefmcwsar |