ELEC ENG 4069/7059 Radar Principles & Systems
Task 3Assignment 3
Due 11:59pm Sunday 5 June 2022
Question 1. A L-band radar operates at a carrier of 1GHz. It observes an aircraft moving through space in a straight line at a speed of 300kmph. The aircraft approaches from the east, flies directly overhead of the radar at an altitude of 10km, and continues to the west. Assume the radar antenna tracks the aircraft so it always appears in its beam.
(a) Sketch the target’s observed Doppler frequency as it flies from east to west through the airspace.Clearly label your plot.
(b) Suggest a suitable pulse repetition frequency (PRF) for this radar.
(c) Estimate the maximum approximation error for this scenario if the formula fd = -2vr/? is used instead of the full expression.
(d) Determine the Doppler resolution if the radar uses bursts of 10 pulses, each of duration 50ns, tomeasure Doppler shift. Use the PRF you suggested in part (b).
[4 marks]
Question 2. When using pulsed radars to measure Doppler shifts in targets, an ambiguity exists if the target Doppler shift is greater than ±PRF/2. One possible way to get around this is to use multiple, “staggered” PRFs simultaneously (perhaps at different carrier frequencies). This generates multiple Doppler shift measurements, with the result being equivalent to a single PRF that is higher than any of the PRFs used.
Consider one such radar with three PRFs: 15kHz, 18,kHz and 21kHz. Assume the operating carrier to be 10GHz.
(a) Calculate the Doppler shifts measured from each PRF used for a target moving at 580m/s.
(b) Another target generates Doppler shifts of -7kHz, 2kHz, and -4kHz at the three PRFs, respectively. What can you say about the target’s velocity?
[2 marks]
Question 3. Write a summary of the principles behind synthetic aperture radar (SAR) imaging. It will need to explain how the technique allows scatterers to be resolved along both range and cross range dimensions.
[3 marks]
Question 4. Use Matlab to simulate the SAR case 1 in Chapter 21 of the textbook. Write code that will generate the radar returns for the scenario discussed in sections 21.5.6. and 21.5.7, and process the returns using the DBS processing scheme to achieve the image shown in figure 21-27. You can assume ideal propagation and the target consists of 5 spatially separated point scatterers with the same RCS
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values, arranged in a similar geometry (you will need to choose the exact coordinates). Other assumptions: broadside imaging and isotropic antennas (i.e. no variation in gain for different azimuth angles). Your code must also plot out the high resolution range profiles during the processing.
[6 marks]
BWN 18/05/2022
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