Identification of Objects Using Complex Resonances

Student: Wei-Cher Chen

Supervisor: Unknown

Category: Engineering Thesis Project - Electrical

Radars, as the name suggests, were traditionally used for radio detection and ranging. Nevertheless, advancement in technology has made it possible for using them as a sensor to identify or classify targets. In this thesis, the feasibility of using the Complex Natural Resonances (CNR’s) or poles to classify simple targets is demonstrated. Backscattering occurs when an incident wave first hit a conducting target. The backscattered field obtained is the frequency response of the target. From the frequency response, we can get the impulse response of the target by using Inverse Fourier Transform technique. The step response of the target can also be obtained by convoluting the impulse response with a unit step function. The CNR’s of the target can then be extracted from the impulse response or step response signals.

In this thesis, we will be considering only two of the most popular CNR’s extraction techniques, namely the Prony’s method and the Matrix Pencil method. It can be proven from the results obtained from this thesis that Matrix Pencil method is better than Prony’s method in term of noise performance and estimating the real poles. Experiments involving perfectly conducting thin wires of length 13cm, 14cm, 15cm and 1m in free space were conducted by using the FEKO program to generate the wires. It is observed that as the length of the wire increases, the resonant frequencies of the wire will decrease. This proves that the CNR’s are dependent on the target’s shape or size. A measure, by the name of Variance Accounted For (VAF), for comparing two signals was used extensively in this thesis. It was used to compare the original transient response (impulse response or step response) with the transient response reconstructed by poles. From the signal reconstruction results obtained, we can see that the VAF between the reconstructed signal and the original signal increases as the number of poles uses to regenerate the signal increases. Time-frequency behaviour of the CNR’s was also examined and it is observed that as the time increases, the stability of the CNR’s increases, but the strength of the CNR’s decreases.

Experiment on extracting the poles from the step response and impulse response of the target was carried out. Analysis shows that the step response of the target gives a better result in term of estimating the real poles.

Thesis Document (PDF)