Through-Wall Imaging With UWB Radar System - KEMT FEI TUKE

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2.2 Through-Wall Radar Basic Model 8 a) b) Fig. 2.1.3: M-sequence UWB radar system. a) fc2 = 9 GHz b) fc1 = 4.5 GHz. where r, θ, ϕ are spatial coordinates, and n is a discrete time, Zc and Z0 impedances of the feed cable and free space respectively, and c is the speed of light in vacuum. The voltage time evolution applied to the TX antenna is denoted VS(n), hT X is the transfer function for the emitting antenna and ∗ represents the convolution. The received voltage from RX antenna VR is then: VR(n) = √ Zc √ hRX(θ, ϕ, n) ∗ E Z0 meas (n) (2.2.2) where hRX is the transfer function of the receiving antenna, and E meas (n) is the field at the RX antenna. VS(n) and VR(n) are scalars due to the fact that the antenna integrates all spatial components into one signal. The process that transforms E rad into E meas depends on the different travel signal paths and is denoted temporarily as an unknown impulse response X(r, θ, ϕ, n). The received voltage thus becomes: VR(n) = √ Zc √ hRX(θ, ϕ, n) ∗ X(r, θ, ϕ, n) ∗ E Z0 rad (r, θ, ϕ, n). (2.2.3) If the 1/r dependency is taken out of the definition of E rad all antenna terms could be combined into one term hA: VR(n) = 1 r hA(θ, ϕ, n) ∗ X(r, θ, ϕ, n). (2.2.4) hA contains the contributions of the measurement system to the signal. It can be accurately measured only in lab conditions but it is very difficult and exacting challenge, that requires too precise measurements. Antenna crosstalk effects means signal traveling directly from the transmitter to the receiver. This signal is thus constantly present in all the measurements
2.3 SAR Scanning 9 and shall remain constant for a fixed antenna setup. The impulse response of the direct path between both antennas will be expressed as CA. The expression for the received field becomes: VR(n) = 1 dT X RX hA(θ, ϕ, n) ∗ CA + 1 r hA(θ, ϕ, n) ∗ X1 (2.2.5) where X1 represents the other (non-direct) paths between the antennas, and dT X RX is the direct distance between TX and RX. The first term can be measured (calibrated) by pointing the antenna system to the anechoic chamber room, so that X1 becomes zero. It can thus be easily subtracted out of any measured data. The second term contains information about eventual target presence, and thus it is the most interesting one. X1 contains a combination of the impulse responses of target hT and clutter hC. X1 = hT + hC. (2.2.6) Here, targets are behind wall scatterers we want to detect, while clutter is anything else which adds misinformation to the signal. A typical clutter examples, presents in most of the measurements are the multiple reflections inside wall, multiple reflections between walls inside the room, multiple reflections between objects and walls or objects itself, non constant permittivity in wave propagation, moving trees in outside measurements, false objects received from behind antennas, etc. The model of the received signal (2.2.5) becomes: VR(n) = 1 dT X RX hA(θ, ϕ, n) ∗ CA(n) + 1 r hA(n) ∗ (hT (n) + hC(n)) + noise. (2.2.7) The last term noise is added to represent measurement noise which is not added to the signal due to a reflection, but due to the measurement system itself. Even if most of the variables in (2.2.7) could be measured, it is very difficult to measure them precisely. In practical measurements only VR(n) is measured what is summation of all these variables. This is the first source of systematic error. One stationary measurement of VR(n) is the so called A-scan and represents impulse response of the measured environment including impulse response of the whole measurement system, clutters, noise, and systematic errors. 2.3 SAR Scanning Only one impulse response from the whole environment is obtained in case when the antennas are stationary during measurements. In order to obtain more information about the investigated objects and to narrow antenna flaring angle beam, the Synthetic Aperture Radar (SAR) scanning is applied.
Page 1 and 2: TECHNICAL UNIVERSITY OF KOˇSICE Fa
Page 3 and 4: Acknowledgement I give a sincere gr
Page 5 and 6: CONTENTS v 3 Goals of Dissertation
Page 7 and 8: LIST OF FIGURES vii List of Figures
Page 9 and 10: LIST OF FIGURES ix 4.4.3 Aquarium f
Page 11 and 12: LIST OF FIGURES xi List of Symbols
Page 13 and 14: LIST OF FIGURES xiii kx - Horizonta
Page 15 and 16: Chapter 1 Introduction 1.1 Motivati
Page 17 and 18: 1.3 Thesis Organization 3 In additi
Page 19 and 20: Chapter 2 State Of The Art 2.1 UWB
Page 21: 2.2 Through-Wall Radar Basic Model
Page 25 and 26: 2.4 Calibration and Preprocessing 1
Page 27 and 28: 2.4 Calibration and Preprocessing 1
Page 29 and 30: 2.5 Radar Imaging Methods Overview
Page 55 and 56: Chapter 4 Selected Research Methods
Page 57 and 58: 4.1 Through-Wall TOA Estimation 43
Page 71 and 72: 4.2 Measurements of the Wall Parame
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4.2 Measurements of the Wall Parame
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4.3 Highlighting of a Building Cont
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4.4 Measurements of the Practical S
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5.1 Conclusion and Future Work 85 5
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50 100 150 200 250 300 350 400 Z 45
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50 100 150 200 250 300 350 400 Z 45
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50 100 150 200 250 300 350 400 Z 45
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Z [cm] Z [cm] 50 100 150 200 250 30
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Z [cm] 50 100 150 200 250 300 b) Em
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BIBLIOGRAPHY 99 [13] T. W. Barrett,
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BIBLIOGRAPHY 101 [46] G. Derveaux,
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BIBLIOGRAPHY 103 [81] S. Kidera, T.
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BIBLIOGRAPHY 105 [115] J. Sachs, M.
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BIBLIOGRAPHY 107 [150] O. Yilmaz, S
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Through-Wall Imaging With UWB Radar System - KEMT FEI TUKE

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