Abstracts of MSc Theses: 1992

List of MSc Theses: 1992

1. M del Mistro A Study of Bistatic Radar and the Development of an Independent Bistatic Radar Receiver.

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Del Mistro M

Abstract:

This thesis introduces concepts about bistatic radars, and their history. Geometry and various measurements are also discussed. A documented receiver system built is also available within this thesis.

This report contains a literature review of bistatic radar and also describes an experimental L-Band bistatic radar receiver which was built at the University of Cape Town.

In a bistatic radar, the transmitter and receiver are separated by an amount which is comparable to the distance to the targets which are being displayed. The separation of the transmitter and receiver cause various parameters to change when comparing the bistatic radar to a monostatic radar. Some of these parameters are listed below.

1. The radar range equation is now a function of RT2RR2 and no longer RM4. The gain of the transmitter and receiver antenna must be taken into account as two different antennas are being used.
2. In a monostatic radar the constant range contours form circles around the collocated transmitter and receiver, whereas in bistatic radar they form ellipses and the transmitter and receiver are the foci of the ellipses.
3. The constant power contours of a monostatic radar are also circles. In a bistatic radar they are ovals surrounding the transmitter and receiver. As the ovals get closer to the line separating the transmitter and receiver (baseline) the ovals collapse and start forming separate circles around the transmitter and receiver.
4. The coverage of a bistatic radar is the area which is illuminated simultaneously by both the transmitter and the receiver. The coverage area can never exceed that of a monostatic radar.
5. The range and cell area resolution degrades as the target approaches the baseline. In order to compete with a monostatic radar very narrow transmit and receive antenna beams are required.
6. Due to the separation of the transmitter and the receiver, a PPI display will be distorted. This distortion is commonly called bistatic distortion.
7. The bistatic radar target cross section (RCS) varies according to target position relative to the transmitter and the receiver. When the target crosses the baseline, its forward RCS is observed. The forward RCS is sometimes 15dB larger than the monostatic reverse RCS. As the target moves further away from the baseline the bistatic RCS starts approximating the monostatic RCS.
8. As the cell area (area of ground illuminated by the transmitter and receiver antenna) of a bistatic radar is larger than that of the monostatic radar near the baseline, the bistatic radar is inherently more susceptible to clutter.

The receiver must maintain synchronization in receiver azimuth and PRF, at all times, in order to correct for bistatic distortion on a PPI display. This distortion is corrected by converting the transmitter-to-target azimuth to the receiver-to-target azimuth and determining the target-to-receiver range which is a function of the delay time. The delay time is the time difference between the direct pulse and the reflected pulse. This will cause the trace on the display to move in a complex pattern, hence correcting this distortion.

A bistatic radar receiver was built for the Electrical Engineering Department at UCT. The purpose of the radar is to monitor aircraft approaching and departing from DF Malan Airport. The motivation for this project is to utilise one of the main advantages of the bistatic radar.

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