Commensal radar makes use of illuminators of opportunity to transmit the illuminating RF energy that is in turn used to detect targets of interest. This implies making use of illuminators that are 3rd party to the radar system and that are often not intended for radar operation. This allows the radar system to be low-cost, as it does not require its own transmitter subsystem nor the license to operate such a transmitter. The prototype system under development makes use of the commercial FM broadcast band (88 to 108 MHz) as the illuminating source.
Four receiver sites (marked by ‘R’) were deployed around the Southern part of the Western Cape to concurrently detect commercial airlines going in and out of Cape Town International Airport.
Image 00: The blue tracks show the ADS-B derived flight paths of some of the aircraft that were detected.
A region of interest (shown by the red overlay) was established, where all sites were able to detect the aircraft, and a week-long deployment was arranged to collect data. Each site was equipped with 2 antennas, one to capture a reference signal directly from a transmitter site (mark by ‘T’) and a second one to survey the region of interest. The sites then had digitising receivers, which output complex baseband sample data. This was recorded to a laptop as well as to a GPU equipped processing server, which generated range/Doppler maps on the fly. This allowed the radar performance at each site to be monitored in real time.
The Donkerhoek site was on a farm on the side of the mountain; the site was only accessible by a high clearance vehicle.
Image 01: The Donkerhoek site and equipment setup.
Image 02: The equipment setup at the Donkerhoek site.
Atlantic Beach Site
The Atlantic beachsite made use of the CSIR’s Radar and EW trailer and the equipment setup. The trailer has an inflatable telescopic mast, which can be raised to 30 feet. This is useful when used in conjunction with the terrain for obtaining separation between reference and surveillance antennas to in turn, improve the signal to interference ratio.
Image 03: The trailer and mast at the Atlantic Beach site
Image 04: Inside the trailer at the Atlantic Beach site
The Malmesbury site and equipment setup; as shown, these remote sites made use of generators to power the radar hardware.
Image 05: The Malmesbury site and equipment setup
Image 06: The Malmesbury site
At the Kalbaskraal site, a spectrum monitoring van was used, as it contains receiver hardware that is compatible with the radar system as well as a telescopic mast and inverter to power the equipment.
Image 07: The Kalbaskraal site and equipment setup.
Image 08: The equipment inside the spectrum monitoring van
Image 09: The Kalbaskraal team, being out in the farmlands, encounters a flock of sheep.
Image 10: Flock of sheep
Before the radar trials started, several possible sites were investigated. This photo shows the FM transmitter for the Franshoek valley, which was visited while doing site tests in the Franshoek valley.
Image 11: FM transmitter for the Franshoek valley.
Equipment tests at Atlantic Beach Site
After the necessary multisite data had been captured, the team use the spare day in the measurement plan to do some equipment tests at the Atlantic beach site.
The photos show setups for comparison between vertical and horizontal polarisations of surveillance antenna and comparisons between receiver equipment respectively.
Image 12: Atlantic beach site – comparing vertical and horizontal polarisations of surveillance antenna.
Image 13: Equipment setup inside the van
During the testing at Atlantic Beach, a new detection range record for this radar system was established. A detection of 550 km bistatic range was established, which shows detection of aircraft approximately 270 km from the site. The can be attributed to the low interference environment that occurs at the Atlantic beach site.
Image 14: Results obtained at the Atlantic Beach site
The data that was collected over the week-long period met the covered scenarios, which were required for the investigation. It is currently being analysed and the results will follow.
The Commensal Radar Team would like to express thanks to Atlantic Beach Golf Estate, as well as Donkerhoek farm for assistance and access to private land during the measurements. We would also like to thank the members of the UCT Radar Remote Sensing Research Group who took time out of their schedules to assist in the measurement campaign.
A big thank you to Craig Tong for putting together this article plus photographs.
Field testing a prototype multistatic commensal radar system
University of Cape Town