{"id":{"repo_id":"cape-town","oai_identifier":"oai:open.uct.ac.za:11427/33820"},"canonical_url":"https://search.dev.ndltd.org/etd/cape-town/oai:open.uct.ac.za:11427/33820","repository":{"repo_id":"cape-town","name":"University of Cape Town","base_url":"https://open.uct.ac.za/oai/request"},"display":{"title":"Time-Offset Fractional-N PLLs for Heterodyne FMCW SAR","abstract":"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.","abstract_html":"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.","abstract_has_math":false,"creators":["Jordan, Darryn Anton"],"institution":"Department of Electrical Engineering","degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Abdul, Gaffar Mohammed Yunus","Inggs, Michael Raymond"],"committee_chairs":[],"committee_members":[],"year":2021,"date_issued":"2021","date_published":"2021","updated_at":"2026-07-22T22:23:47Z","subjects":["Electrical Engineering"],"languages":[],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/11427/33820","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Abdul, Gaffar Mohammed Yunus","Inggs, Michael Raymond"]},{"key":"dc:creator","label":"Author","values":["Jordan, Darryn Anton"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2021-08-24T01:46:56Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2021-08-24T01:46:56Z"]},{"key":"dc:date.issued","label":"Date","values":["2021"]},{"key":"dc:publisher.department","label":"Dc Publisher Department","values":["Department of Electrical Engineering"]},{"key":"dc:type","label":"Dc Type","values":["Doctoral Thesis"]},{"key":"dc:type.qualificationlevel","label":"Dc Type Qualificationlevel","values":["Doctoral","PhD"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Electrical Engineering"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["http://hdl.handle.net/11427/33820"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["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."]},{"key":"dc:title","label":"Title","values":["Time-Offset Fractional-N PLLs for Heterodyne FMCW SAR"]}]}],"canonical_facts":{"dc:contributor.advisor":["Abdul, Gaffar Mohammed Yunus","Inggs, Michael Raymond"],"dc:creator":["Jordan, Darryn Anton"],"dc:date.accessioned":["2021-08-24T01:46:56Z"],"dc:date.available":["2021-08-24T01:46:56Z"],"dc:date.issued":["2021"],"dc:description.abstract":["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."],"dc:identifier.uri":["http://hdl.handle.net/11427/33820"],"dc:publisher.department":["Department of Electrical Engineering"],"dc:subject":["Electrical Engineering"],"dc:title":["Time-Offset Fractional-N PLLs for Heterodyne FMCW SAR"],"dc:type":["Doctoral Thesis"],"dc:type.qualificationlevel":["Doctoral","PhD"]},"updated_at":"2026-07-22T22:23:47Z"}