“Africa and remote sensing are not for sissies”

South African Synthetic Aperture Radar II

 

Transmitter

The basic function of the transmitter system is the up-conversion of the base-band signals through a series of mixers, amplifiers and filters for power amplification and finally transmission. The exact details of each up-conversion stage will not be covered, although a brief description was given in the previous section (see block diagram below).

The base-band signals provided are the I and Q “chirp” signals provided by the Digital Pulse Generator. A “chirp” waveform is essentially a linearly modulated sinusoid. The reason for the use of a chirp waveform is to aid in the post processing pulse compression. Pulse compression serves to improve the range resolution of the final radar system. The final user specified range resolution is 2m X 2m.

The system bandwidth used is 100 MHz. This greatly improves our range accuracy, but also increases the system requirements to be able to handle the bandwidth.

RF switches inserted at each frequency stage allows the user to perform “loop back” tests to determine whether the system is operating within the specified power levels i.e. signals from IF stages in the transmitter are routed to the appropriate stages of the receiver where the final output of the receiver can be measured.

As explained previously the multiple frequency modes of operation are facilitated by the RF switches. The radar unit currently can operation at X band and L band, with the addition of a few more switches and mixers, an Operational C band system is possible.

Due to the lack of appropriate equipment, the testing of the radar system will be limited to high power L-band and low power X-band. The high power components were kindly donated by Reutech Radar Systems. Testing of the radar system at this stage is currently being investigated. Any progress in this field will be posted on the website.

 

A grown up tracking radar, courtesy of RRS

Block diagram of the Transmitter stage for the SASAR II system

The credit for the design and construction of the Transmitter is given to Darren Coetzer, who completed a Masters of Science in Electrical Engineering from the University of Cape Town in 2004.