Coetzer, Darren. Design and Implementation of a X-band Transmitter and Frequency Distribution Unit for a Synthetic Aperture Radar. MSc Dissertation. Department of Electrical Engineering, University of Cape Town, 2004.
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 analogue transceiver to communicate with the digital circuitry.
It is found that the chirp signal produced is of satisfactory fidelity. LO feedthrough, however, is superimposed at the chirps´ centre frequency. As a result of previous stages, spurious signals exist at 16 MHz offset from the chirps´ centre frequency and at 9142 MHz. The system transfer function reveals that 2 dB roll-off is present at the outer frequencies of the chirp signal. Group delay in the transmitter filters and amplifiers is held responsible for this.