Back to list of Group's MSc Theses
Abstract:
Synthetic aperture radar (SAR) can provide high-resolution images of extensive areas of the earth´s surface from a platform operating at long ranges, despite adverse weather conditions or darkness. A local consortium was established to demonstrate a consolidated South African SAR ability to demonstrate to the local and international communities, by generating high quality images with a South African X-band demonstrator. This dissertation forms part of the project. It aims to describe the design and implementation of the transmitter and associated frequency distribution unit (FDU) for the SASAR II, X-band SAR.
Although the transmitter and FDU are two separate units, they are ultimately linked. The transmitter has the task of taking a low-power, baseband, chirp waveform and, through a series of mixers, filters and amplifiers, converting it to a high-power, microwave signal. The FDU is essentially the heart of the transceiver and provides drive to all the mixer local oscillator (LO) inputs. It also clocks the DAC and ADC which allow the essentially analog transceiver to communicate with the digital circuitry.
A chirp signal is generated via quadrature modulation of two chirps with half the final, desired bandwidth. Through careful design procedure this signal is upconverted to X-band with effort taken to minimise signal distortion.
It is found that the chirp signal produced has satisfactory amplitude distribution. LO feedthrough, however, is superimposed at the chirp's centre frequency. As a result of previous stages, spurious signals exist at 16MHz offset from the chirp's centre frequency and at 9142MHz. The system transfer function reveals that 2dB attenuation is present at the outer frequencies of the chirp signal. Group delay in the transmitter filters and amplifiers is held responsible for this, but this has not been quantified here, but once the receive chain is operational, the system impulse response can be tested.
Back to list of Group's MSc Theses
Abstract:
This dissertation focuses on the design and implementation of an X-band receiver for use in the South African Synthetic Aperture Radar (SASAR II) project. The SAR will be used to demonstrate the capability of building a high resolution X-band imaging radar in South Africa. The design starts by investigating the maximum power return from different targets over a swath width with changing incidence angles.
A receiver-power-level table and diagram were constructed, with the power return from a trihedral corner reflector as maximum input power and thermal noise as the minimum input power to the receiver. The output of the receiver, which has to be fed to the input of an analogue-to-digital converter (ADC), is limited by the ADC's maximum operating input power.
Amplifiers, attenuators and mixers were chosen to implement a dual-stage downconversion from a radio frequency (RF) of 9300 MHz to a 2nd IF of 1300 MHz and then to a 1st IF of 158 MHz. A sensitivity time control (STC) is implemented in the receiver to cater for the limited dynamic range of the ADC.
The power return varies with range and hence, time. Thus, an STC will correct for low return power, at far range, by boosting the received signal and attenuating large return power, at close range, ideally providing a fairly constant power return at the receiver output. A manual gain control (MGC) is also needed in the receiver, such that none of the components are driven into saturation. The gain control is switched on when large targets are expected to fall in the swath width, otherwise it is switched to a minimum for targets with low backscattered power.
The tests that were carried out on the receiver components showed that all the components operated very close to their specifications. The cascaded filters work well in tailoring the front-end 3-dB bandwidth to close to the required 3-dB bandwidth. The receiver was designed to have enough gain to boost the maximum power received to within the operating range of the ADC, without saturating any components in the receiver. The noise figure test showed a noise figure of 4:20 dB. This is 1.73 dB higher than the calculated noise figure of 2.47 dB which is a result of an underestimation of the losses in the system.
Back to list of Group's MSc Theses
Abstract:
The accuracy of a combined Optronics and Radar Tracker system is investigated in this dissertation.
The Tracking Accuracy Measurement (TAMS) was designed to exploit the positional accuracy of differential Global Positioning System (dGPS) technology to qualify a 60km range X-band combined Optronic and Radar Tracker System.
In essence, a roving GPS receiver, capable of measuring high dynamic movement, is mounted onboard an airplane and records the target position as it is tracked by the sensor. At the sensor, a similar recording station records the GPS position of the sensor, and is carefully surveyed into the co-ordinate system of the sensor. The TAMS also records the sensor output, which is carefully time-stamped with GPS time. Post mission, the raw GPS is differentially corrected.
An algorithm was written in Matlab for the purpose of comparing the dGPS measurements and the sensor measurements, once suitable interpolation and correction for sensor latency has taken place. The accuracy of the sensor latencies were investigated, and it was found that the latencies for both the Optronic and Radar sensors were off by a marginal time delay. It was concluded that the direction and speed of the airplane would account for this anomaly, but a more in-depth investigation should be considered.
The accuracy of the Tracker was calculated using statistical methods, and the accuracy computed for the data received for this dissertation was compared to the required Tracker specifications. Because only data from the 5km and 10km range bin was available for the analysis, the Tracker could only be quailified at these range bins. The result of the statistical analysis showed that the Tracker system meets specification at the 5km and 10km range bin.
Back to list of Group's MSc Theses
Abstract:
This dissertation describes the design, implementation and testing of the Radar Digital Unit (RDU), a subsystem for the South African Synthetic Aperture Radar II (SASARII). The SASARII is an airborne demonstrator SAR system for a spaceborne SAR. The demonstrator system parameters, such as bandwidth reflect the desired Spaceborne SAR parameters. The Radar Digital Unit is comprised of three modules: 1.Digital Pulse Generator (DPG) that outputs a chirp every Pulse Repetition Interval (PRI) for transmission 2.Sampling Unit (SU) which samples the received IF signal every PRI, forms a packet of samples and flight information and sends the packet for storage 3.Timing Unit (TU) which distributes triggers to the SASARII system every PRI. Based upon the user requirements, Parsec a company in Pretoria, South Africa, supplied generic hardware for the RDU. SASARII firmware was developed for each module at Parsec under their guidance and support. The testing of the three modules was conducted at Parsec and the Radar Remote Sensing Group. Each module was tested individually. The following was concluded from the test results: 1.The DPG firmware and hardware operates to specification 2.The SU firmware functions correctly 3.The TU firmware simulates correctly. But testing uncovered a possible hardware bug, and Parsec was informed. At time of writing this dissertation the problem had not been solved.
Back to list of Group's MSc Theses
Abstract:
A device has been designed that cancels the leakage signal between the transmit and receive antenna in a Stepped Frequency Continuous Wave Ground Penetrating Radar. The front end of the radar operates at high signal levels and, as a result, a large signal is coupled directly from the transmit to the receive antenna. This signal uses a significant part of the dynamic range of the data-capturing device, an analogue-to-digital converter (ADC). The objective of this cancellation is thus to increase the effective instantaneous dynamic range of the radar system.
Simulations show that 10-bit amplitude and phase resolution in the digital cancellation circuit would achieve maximum cancellation in the presence of phase noise and other sources of error. This result is confirmed when the hardware is tested.
The device was constructed and operates as intended. Tests show that cancellation exceeding 53dBm is possible through careful calibration. It was concluded that the device could successfully be integrated into the SFCWGPR and that it would achieve an increase in the instantaneous dynamic range.
Back to list of Group's MSc Theses
This page was last updated in September 2007 (RL)