Resolution of GPR bowtie antennas: An experimental approach Fernando I. Rial, Manuel Pereira, Henrique Lorenzo, Pedro Arias, Alexandre Novo PII: DOI: Reference:
S0926-9851(08)00056-6 doi: 10.1016/j.jappgeo.2008.05.003 APPGEO 1697
To appear in:
Journal of Applied Geophysics
Received date: Accepted date:
9 October 2007 13 May 2008
Please cite this article as: Rial, Fernando I., Pereira, Manuel, Lorenzo, Henrique, Arias, Pedro, Novo, Alexandre, Resolution of GPR bowtie antennas: An experimental approach, Journal of Applied Geophysics (2008), doi: 10.1016/j.jappgeo.2008.05.003
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT RESOLUTION
GPR
BOWTIE
ANTENNAS:
AN
EXPERIMENTAL
2
APPROACH
3
Fernando I. Rial, Manuel Pereira, Henrique Lorenzo, Pedro Arias, Alexandre Novo.
4
Department of Natural Resources and Environmental Engineering, University of Vigo.
5
Campus A Xunqueira s/n. 36005-Pontevedra, Spain.
6
[email protected] Ph: +34 986801935 Fax: +34 986801907
RI
OF
PT
1
SC
7 ABSTRACT
9
Since target reflections directly depend on the emitted pulse characteristics, a key factor for
10
carrying out a successful GPR survey is to know as much as possible about the transmission
11
features of the antennas used. This information is very important in order to choose the right
12
antennas and set the appropriate configuration parameters for a specific survey. With this in mind
13
this paper deals with the development of a set of laboratory experiments on the resolution
14
capabilities of three bow-tie antennas at frequencies of 500, 800 and 1000 MHz. Results from these
15
measurements give a first estimation of the resolution of the antennas under test, showing the
16
advantage of performing experiments rather than relying only on theoretical assumptions. The
17
results are also expressed in terms of the central wavelength for each antenna and compared with
18
some theoretical estimations proposed in the specialized bibliography.
MA
D
TE
AC CE P
19
NU
8
20
KEYWORDS
21
GPR, bowtie antennas, horizontal resolution, vertical resolution.
22 23
1. INTRODUCTION
24
Despite GPR being the most widely used ultra-wide band radar (Yarovoy and Ligthart, 2004), part
25
of the antennas construction is still a process done mainly by hand. Therefore, antennas from the
26
same company and with the same nominal frequency present, for instance, slight differences in
27
terms of the emitted source wavelet or in the radiation pattern. In general, as the frequency of the
28
antenna increases so does the resolution, but the penetration capacity of the signal decreases
29
(Daniels, 2004). This trade-off is a well-known fact in GPR, although surprising results in terms of
30
resolution are being achieved with a priori low-medium frequency antennas by means of 3D data
31
(Grasmueck and Viggiano, 2006).
ACCEPTED MANUSCRIPT To perform a suitable data acquisition it is essential to select the appropriate radar antennas for each
33
particular survey. Commercially available GPR antennas typically range from 10 MHz to 4 GHz,
34
having their own particular transmitting and receiving characteristics and capabilities. Not knowing
35
of the different emission parameters of the antennas, as well as other characteristics of the emitted
36
signal, constitutes an added difficulty for carrying out GPR surveys. In order to address this
37
problem, studies made by several researchers have contributed to the continuous development of
38
survey techniques. Several antenna aspects have been studied by many engineers and researchers,
39
such as the influence of antenna height (van der Kruk, 2003; Bloemenkamp and Slob, 2003),
40
antenna radiation pattern (Valle et al., 2001; Millard et al., 2002a), or the polarization scheme
41
adopted (Roberts and Daniels, 1996; Radzevicius and Daniels, 2000). A system’s resolution
42
capacity is also an important matter, and it is of particular interest in road evaluation (Al-Quadi and
43
Lahouar, 2005; Saarenketo, 2006) and general civil engineering (Yelf and Carse, 2000; Millard et
44
al., 2002b) where millimetre resolution in both - the vertical and horizontal planes-, is sometimes
45
required for conducting GPR surveys at an ‘audit’ level (Yelf, 2004).
46
Resolution can be understood, as proposed by Annan (2003), as the radar system capacity to
47
discriminate individual elements in the subsoil. It is essentially divided into two topics: vertical
48
(down-range, depth or longitudinal) resolution (∆V) and horizontal (cross-range, angular, lateral, or
49
plain) resolution (∆H), as shown in Figure 1.
50
Vertical resolution provides knowledge about the equipment’s ability to differentiate, in time, two
51
adjacent reflections as different events (Lorenzo, 1996). For the type of systems considered in this
52
paper (pulsed radars), the vertical resolution mainly depends on the duration of the radar pulse,
53
which is related to the central frequency of the antenna.
54
Taking into account Figure 2, ∆t can be defined as (Anan, 2003):
55
∆t = t 2 - t1 =
56
where t1 and t2 are the travel times for reflections R1 and R2 and v is the wave velocity.
57
In general, it is accepted that two close events can be distinguished if the targets are separated in
58
time by a difference of half the effective pulse duration τP, which is obtained from the width of the
59
signal envelope at its -3dB level (Millard et al., 2002a). Therefore, the expected spatial vertical
60
resolution can be calculated from the effective duration τP of the radar pulse and the wave
61
propagation velocity in the medium (Annan, 2003):
AC CE P
TE
D
MA
NU
SC
RI
PT
32
2∆r (1) v
ACCEPTED MANUSCRIPT τP v τc = P 4 4 εr
62
∆V ≈
63
This theoretical approach doesn't take into account that the characteristics of the initial radar signal
64
varies as it propagates. In most natural materials, the attenuation of the electromagnetic waves
65
increases with frequency, widely known as the dispersion effect. This low-pass filter effect within
66
the propagating materials causes an increase in the duration of the pulse and, therefore, worsens the
67
resolution. As the wave propagates, it loses its high frequency components; although in some cases
68
the resolution is approximately independent of this loss. Earth materials with significant water
69
content tend to have higher attenuation properties but this characteristic is balanced out with the
70
reduction of the pulse length due to a slower wave velocity in wetter materials (Daniels, 2004).
71
Horizontal resolution indicates the minimum distance that should exist between two reflectors
72
located next to the other at the same depth (parallel to the analyzed medium surface) so that the
73
radar detects them as separate events (Daniels, 1988). The horizontal resolution of any antenna
74
depends on the trace interval, the beam width, the radar cross section of the reflector and the depth
75
of the target. The trace interval is usually a controllable factor that the operator can adjust before
76
data acquisition. The beam geometry is a different matter, because it depends on the characteristics
77
of the antenna and the propagation medium (Pérez-Gracia, 2001). A narrower beam gives a better
78
horizontal resolution. The beam can be approximately considered as the cone of energy that
79
intersects with the reflector surface, illuminating an area that is called antenna footprint as shown in
80
Figure 3.
81
The zone of influence is defined as the area which can contain a second target that cannot be
82
uniquely resolved. So that horizontal resolution can be identified with the footprint size. An
83
estimation of the antenna footprint size can be obtained by different mathematical expressions
84
proposed in the specialized bibliography. A common approximation identifies the footprint with the
85
diameter (D) of the first Fresnel Zone (Pérez-Gracia, 2001):
86
AC CE P
TE
D
MA
NU
SC
RI
PT
(2)
∆H = D =
λ2 + dλ 4
(3)
87
Another expression to define the diameter of this antenna footprint was proposed by Conyers and
88
Goodman (1997):
89
∆H = D =
λ 2d + 2 εr +1
(4)
ACCEPTED MANUSCRIPT In these two equations, λ is the wavelength; d is the vertical distance between the antenna and the
91
reflector surface and εr is the relative permittivity of the medium. Other researchers (Daniels, 2004)
92
define the horizontal resolution as the distance between the half power points of the spatial response
93
of the scatterer at the plane of the surface:
94
∆ H = 4d
95
This approximation does not take into account the antenna beam pattern in either the x or y axes.
96
However, it does indicate that horizontal resolution improves as the attenuation (α) increases,
97
provided that adequate signal to noise and signal to clutter ratios are maintained. (Daniels, 2004).
98
In particular, this work deals with the development of a set of experiments in order to analyze the
99
resolution capacity of three bow-tie antennas at frequencies of 500, 800 and 1000 MHz, making an
ln 2 ( 2 + αz )
PT
90
MA
NU
SC
RI
(5)
experimental approach to their real resolution capacity and comparing it with theoretical
101
estimations. The layout of this paper is as follows: Section 2 focuses on the methodology proposed
102
to carry out the antenna resolution tests. These experiments are carried out in air and using two
103
timber structures designed and constructed for this purpose. Section 3 includes the results of the
104
experiments for the three antennas under test (AUT). The experimental results are also expressed in
105
terms of the central wavelength for each antenna, being compared with the results estimated with
106
equation 2 for the vertical resolution and with equations 3-5 for the horizontal resolution. Finally,
107
Section 4 summarizes the contributions of this paper and discusses possibilities for future research.
TE
AC CE P
108
D
100
109
2. METHODOLOGY
110
Two timber, ladder-like, structures were designed and constructed with steps at every 5cm. For the
111
horizontal resolution test, these structures were hung from the ceiling, parallel to the floor (Figure
112
4). For the vertical resolution tests, the ladders were placed vertically and fixed in a wooden support
113
as shown in Figure 5.
114
Two metallic bars of 3cm in diameter, and two wooden bars of 4 cm width x 2.5 cm height, were
115
used on the test where air was the propagation medium. In both cases, the antennas were mounted
116
on a trolley that was moved parallel to the ladders and perpendicular to the bars direction.
117
Experiments started with the two metallic bars placed together and, for each new measurement, the
118
gap between them was increased by 5cm until the bars were clearly distinguishable in the data. The
119
same tests were repeated with wooden bars. Measurements were made at three different distances,
120
one in the far-field region and the other two in the near-field region, so that the variation of the
ACCEPTED MANUSCRIPT resolution can be analyzed as the reflectors move away from the antenna. Within the far-field region
122
of the antenna, the electric field E and magnetic field H are locally in-phase and perpendicular to
123
each other. In the near-field region around the antenna, the description of the electromagnetic
124
radiation is more complex. The separation between far and near-field have been chosen by
125
considering the Rayleigh criterion (Balanis, 2005):
126
2D 2 d= λ
127
where D is the dimension of the dipoles, and λ is the wavelength of the pulse. Because the size of a
128
medium-high frequency GPR antenna is small compared to the wavelength, equation 7 gives a
129
better approximation (Yaghjian, 1986):
130
2D 2 +λ d= λ
PT
121
MA
(7)
NU
SC
RI
(6)
131
In other words, the Rayleigh distance should actually be measured from the outer boundary of the
133
reactive near-field of the antenna. A value of 3λ is also regarded by some authors as a good
134
approximation to the separation between near- and far-field regions (Millard et al., 2002a).
135
For all tests (horizontal and vertical) performed in this work, the same stacking (8 scans averaging)
136
and trace interval (1.1 cm) have been used. The emitted pulse and frequency content of the AUTs
137
are shown in Figure 6, and their effective pulse duration and central frequency are summarized in
138
Table 1. It is not the aim of this paper to give a detailed explanation of how they have been
139
obtained, which can be found in the work of Rial (2007) where a set of experiments were made in
140
order to analyze the characteristics of the source wavelet emitted for each AUT.
AC CE P
TE
D
132
141 142
3. RESULTS
143
3.1 Vertical Resolution (∆V)
144
For each AUT and for each set of bars, 10 radargrams were obtained at different antenna distances
145
(d) (see Figure 2) at near- and far-field (16, 43 and 163 cm for the 1 GHz antenna, 16, 74 and 119
146
cm for the 800 MHz antenna and 10, 85 and 185cm for the 500 MHz antenna). It gives a total
147
amount of 180 radargrams for the whole vertical test. Figures 7, 8 and 9 show some representative
148
radargrams obtained for the three antennas and the measured vertical resolutions have been
149
summarized in Table 2 for the 1GHz antenna, Table 3 for the 800 MHz antenna, and Table 4 for the
ACCEPTED MANUSCRIPT 500 MHz antenna. Tables 2-4 show the results both, in cm and in terms of the antenna central
151
wavelength (with the latter in brackets).
152
It is possible to compare the experimental results with the theoretical vertical resolution from
153
equation 2, taking into account the effective parameters of each antenna (Table 1). The results of the
154
theoretical vertical estimation are summarized in Table 5.
155
As expected, the vertical resolution is better for the higher frequency antennas because of their
156
shorter pulse duration (Table 1, Figure 6) and very similar for the 1 GHz and the 800 MHz
157
antennas, which explains why the results obtained in Tables 2 and 3 were the same for both
158
antennas. Regarding the different materials used in the experiments (metallic and wooden bars), the
159
resolution worsens when metals bars are used, due to their higher electromagnetic contrast, amongst
160
other things. A higher electromagnetic contrast diminishes the energy of the signal that reaches the
161
second reflector, so a bigger separation is needed in order to detect them as discrete events. This
162
effect is more relevant when the reflectors are closer to the antennas and in particular for the 500
163
MHz antenna (Table 4).
164
3.2 Horizontal Resolution (∆H)
165
For each AUT, and for each set of bars, 20 radargrams were obtained at different antenna distances
166
(d) (see Figure 3) at near- and far-field (7, 91 and 147 cm for the 1 GHz and 800 MHz antennas,
167
and 35, 143 and 196 cm for the 500 MHz antenna). It gives a total amount of 360 radargrams for
168
the whole horizontal test. Figures 10, 11 and 12 show some representative radargrams obtained for
169
the three antennas and the measured horizontal resolutions have been summarized in Table 6 for the
170
1 GHz antenna, Table 7 for the 800 MHz antenna and Table 8 for the 500 MHz antenna. Tables 6-8
171
show the results both, in cm and in terms of the antenna central wavelength (with the latter in
172
brackets). The tables also include the theoretical estimations calculated from equations 3, 4 and 5,
173
taking into account the effective parameters of each antenna (Table 1).
174
The horizontal resolution obtained for the 1 GHz and 800 MHz antennas is very similar and much
175
better than for the 500 MHz antenna. As expected, horizontal resolution worsens as the reflectors
176
are moved away from the antennas, mainly because their footprint size gets larger. In the
177
radargrams (a) and (b) of Figures 10, 11 and 12, the differences in the reflected signal for the two
178
types of bars used during the tests can be seen. The influence of the type of bar in the resolution is
179
less noticeable for the horizontal resolution than for the vertical one. This influence only seems
180
significant when the bars are close to the antenna, then the hyperbolas become smaller and the
181
wooden bars can be distinguished better.
AC CE P
TE
D
MA
NU
SC
RI
PT
150
ACCEPTED MANUSCRIPT 182 4. CONCLUSIONS AND DISCUSSION
184
Based on the obtained results, it can be seen that vertical resolution does not change significantly
185
with distance. This result agrees with the lossless nature of the air. In general, the vertical resolution
186
improves using wooden bars. The higher reflection coefficient of the metallic bars makes the tail of
187
the reflected pulse in the first bar (late-time ringing) strong enough to blur the second one when the
188
two bars are close to each other. This effect is especially noticeable in the results obtained with the
189
500MHz antenna in the near-field zone (Table 4), because of its longer pulse duration. Something
190
that should be emphasized is the fact that the results obtained for different antennas seem to
191
converge when the bars are placed far from the antennas and the results are expressed in
192
wavelengths.
193
Vertical resolution is very similar for the higher frequency antennas (1 GHz and 800 MHz) due to
194
their similarities in terms of central frequency and effective pulse duration (Table 1). The minimum
195
vertical resolution achieved is approximately one half of the central wavelength. This value
196
increases until a distance is reached that is equivalent to the central wavelength. The theoretical
197
estimations calculated with equation 2, and the standard practice of using a quarter of the
198
wavelength as the minimum limit for the vertical resolution (Annan, 2003; Millard et al., 2002b),
199
should be regarded as optimistic recommendations when the propagation medium is air, as shown
200
by the results.
201
Horizontal resolution worsens as the reflectors are separated from the antennas because the
202
footprint gets larger. The experimental values range approximately from λ/2 (close to the antenna)
203
to 2λ for the high frequency antennas. Again, the results obtained for different antennas, expressed
204
in terms of wavelengths, seem to converge when the bars are placed far from the antennas. In the
205
horizontal resolution, the influence of the reflector’s material (wooden or metallic) is smaller. As
206
expected, the best resolution is obtained with the 1 GHz antenna as its resolution is slightly better
207
than for the 800 MHz one. The theoretical estimations calculated with equation 3 fit the
208
experimental results better. The other estimations only seem to fit reasonably well when the
209
reflector is close to the antennas. When the separation between the reflector and the antennas
210
increases, they under-estimate the actual capability of the antennas to detect the targets.
211
It is important to remark that the propagation medium was air in all the tests we performed. GPR
212
bow-tie antennas are designed to operate in contact with the ground and the vertical and horizontal
213
resolution in subsoil materials is, in general, better than in air (when expressed in terms of distance).
214
Some authors, such as Shaari et al. (2003), have measured this improvement experimentally in
AC CE P
TE
D
MA
NU
SC
RI
PT
183
ACCEPTED MANUSCRIPT water and concrete, showing the influence of material’s relative permittivity on the antenna central
216
frequency and beam width. For this reason, and for the sake of comparison with other materials and
217
antennas, the experimental results for resolution obtained in this work have been also expressed in
218
terms of wavelength, as proposed by other authors (van der Kruk, 2003; Millard et al., 2002b).
219
The size of the bars, used in the experiments, also has to be addressed. The size was chosen by
220
taking into account the central wavelength of the emitted signal of the antennas in air and also based
221
on the proposal of Millard et al. (2002b). In our opinion, an improvement in the results could be
222
expected, a priori, using thinner bars, however, experiments carried out by other authors are not
223
conclusive in this sense (Pérez-Gracia, 2001; Millar et al., 2002a; Radzevicius et al., 2004; Rial,
224
2007)
225
Finally, despite the fact that the tests were made in a medium with electromagnetic properties that
226
are different to subsoil materials, the experimental approach proposed in this work gives a first
227
estimation of the system capabilities in terms of resolution for the antennas under study; 500 MHz,
228
800 MHz and 1 GHz.
MA
NU
SC
RI
PT
215
TE
D
229 ACKNOWLEDGMENT
231
This research was supported by research grants from Xunta de Galicia (PGIDIT06TIC076E and
232
PGIDITCST37101PR) and University of Vigo. The authors would like to thank Dr Ainhoa G.
233
Gorriti for her helpful suggestions to improve the quality of this work and for review of the
234
manuscript.
235 236
AC CE P
230
237
REFERENCES
238 239
Al-Qadi, I.L., Lahouar, S., 2004, Ground Penetrating Radar: State of the practice for pavement assessment. Materials Evaluation 62 (7), 759-763.
240 241
Annan, P., 2003, Ground Penetrating Radar. Principles, Procedures & Applications. (Sensors & Software, Inc: Mississauga, Canada).
242 243
Balanis, C.A., 2005, Antena Theory: Analysis and Design (3rd Edition), (John Wiley & Sons, Inc.: Hoboken, New Jersey, USA).
244 245 246
Bloemenkamp, R., Slob, E., 2003, The effect of the elevation of GPR antennas on data quality. Proceedings of the second International Workshop on Advanced Ground Penetrating Radar, 201206.
247 248
Conyers, L.B., Goodman, D., 1997, Ground-Penetrating Radar. An introduction for archaeologists. (Altamira Press: Walnut Creek, USA).
ACCEPTED MANUSCRIPT Daniels, D. J., 2004, Ground Penetrating Radar (2nd Edition). IEE Radar, Sonar and Navigation Series 15. (The Institution of Electrical Engineers: London, UK).
251 252
Daniels, D.J., Gunton, D.J., Scott , H.F., 1988, Introduction to subsurface radar. IEE Proceedings, Vol.135, Pt. F, No. 4, 278-320.
253 254 255
Grasmueck, M., Viggiano, D.A., 2006, 3D/4D GPR Toolbox and Data Adquisition Strategy for High Resolution Imaging of Field Sites. Proceedings of 11th International Conference on Ground Penetrating Radar, CD-ROM.
256 257
van der Kruk, J., 2003, Multi-Component GPR Imaging For Different Heights Of Source And Receiver Antennas, Proceedings of 2nd lntemational Workshop on Advanced GPR, 189-194.
258 259
Lorenzo, E., 1996, Prospección geofísica de alta resolución mediante Geo-Radar. Aplicación a obras civiles. PhD Thesis. (CEDEX: Madrid, Spain). (in spanish).
260 261
Millard, S.G., Shaari, A., Bungey, J.H., 2002a, Field Pattern characteristics of GPR Antennas, NDT&E International 35 (7), 473-482.
262 263
Millard, S.G., Shaari, A., Bungey, J.H., 2002b, Resolution of GPR Bow-Tie Antennas, Proceedings of 10th International Conference on Ground Penetrating Radar, 724-731.
264 265 266
Pérez-Gracia, V., 2001, Evaluación GPR para aplicaciones en arqueología y en patrimonio histórico-artístico, PhD Thesis. (Polithechnic University of Catalonia: Barcelona, Spain). (in spanish).
267 268
Radzevicius, S.J., Daniels, J.J., 2000, Ground penetrating radar polarization and scattering from cylinders. Journal of Applied Geophysics 45, 111-125.
269 270
Rial, F., 2007, Characterization and Analysis of GPR Bowtie Antennas. Application in Road Surveys. PhD Thesis. (Vigo, Spain: University of Vigo).
271 272
Roberts, R.L. , Daniels, J.J. , 1996, Analysis of GPR Polarization Phenomena. Journal of Environmental and Engineering Geophysics 1, 139-157.
273 274 275
Saarenketo, T., 2006, Electrical Properties Of Road Materials And Subgrade Soils And The Use Of Ground Penetrating Radar In Traffic Infrastructure Surveys, PhD Thesis. (Oulu, Finland :Oulu University Press).
276 277 278
Shaari, A., Millard, S.G., Bungey, J.H., 2003, GPR Antenna-Medium Coupling Effects : Experimental and 2D FDTD Modelling Results. Int. Symp. on Non-Destructive Testing in Civil Engineering (NDT-CE).
279 280 281
Valle, S., Zanzi, L., Sgheiz, M., Lenzi, G., and Friborg, J., 2001, Ground Penetrating Radar Antennas: Theorical and Experimental Directivity Functions, IEEE Transactions on Geoscience and Remote Sensing 39 (4), 749-758.
282 283
Yaghjian, A., 1986, An overview of near-field antenna measurements. IEEE Transactions on Antennas and Propagation 34 (1), 30-45.
284 285
Yarovoy, A., Ligthart, P., 2004, Ultra-WideBand Technology Today, Proceedings of 15th International Conference on Microwaves, Radar and Wireless Communications, 456-460.
286 287
Yelf, R., Carse, A., 2000, Audit of a road bridge superstructure using GPR, Proceedings of the 8th International Conference on Ground Penetrating Radar, SPIE Vol. 4084, 249-254.
288 289
Yelf, R., 2004, Where is true time zero?, Proceedings of 10th International Conference on Ground Penetrating Radar, 279-282.
AC CE P
TE
D
MA
NU
SC
RI
PT
249 250
ACCEPTED MANUSCRIPT FIGURE CAPTIONS
291
Figure 1. Schematic representation of horizontal and vertical resolution.
292
Figure 2. Reflections from two targets with vertical separation ∆r.
293
Figure 3. Schematic representation of the antenna footprint, which is used to define the horizontal
294
resolution.
295
Figure 4. Ladder structures and methodology used during the horizontal resolution tests.
296
Figure 5. Ladder structures and methodology used during the vertical resolution tests.
297
Figure 6. Characteristics of the emitted pulse in the time and frequency domains for the 1 GHz, 800
298
MHz and 500 MHz antennas under test (AUT).
299
Figure 7. Radargrams of the 1 GHz antenna in a vertical resolution test. The nearest bar was placed
300
at a distance of 63 cm from the antenna.
301
Figure 8. Radargrams of the 800 MHz antenna in a vertical resolution test. The nearest bar was
302
placed at a distance of 74 cm from the antenna.
303
Figure 9. Radargrams of the 500 MHz antenna in a vertical resolution test. The nearest bar was
304
placed at a distance of 85 cm from the antenna.
305
Figure 10. Radargrams of the 1 GHz antenna in a horizontal resolution test. The bars were placed at
306
a distance of 91 cm from the antenna.
307
Figure 11. Radargrams of the 800 MHz antenna in a horizontal resolution test. The bars were placed
308
at a distance of 91 cm from the antenna.
309
Figure 12. Radargrams of the 500 MHz antenna in a horizontal resolution test. The bars were placed
310
at a distance of 143 cm from the antenna.
AC CE P
TE
D
MA
NU
SC
RI
PT
290
ACCEPTED MANUSCRIPT TABLE CAPTIONS
312
Table 1. Effective pulse duration and central frequency for the 1 GHz, 800 MHz and 500 MHz
313
antennas under test (AUT).
314
Table 2. Experimental results of vertical resolution for the 1 GHz antenna. The measurements were
315
made for two types of bars (wood and metal) at three distances (16, 63 and 143 cm). The results are
316
expressed in cm and in terms of the central wavelength of the antenna.
317
Table 3. Experimental results of vertical resolution for the 800 MHz antenna. The measurements
318
were made for two types of bars (wood and metal) at three distances (16, 74 and 119 cm). The
319
results are expressed in cm and in terms of the central wavelength of the antenna.
320
Table 4. Experimental results of vertical resolution for the 500 MHz antenna. The measurements
321
were made for two types of bars (wood and metal) at three distances (10, 85 and 185 cm). The
322
results are expressed in cm and in terms of the central wavelength of the antenna.
323
Table 5. Theoretical vertical resolution of the 1GHz, 800MHz and 500MHz antennas under test.
324
The values are calculated by using equation 2 and the effective values of Table 1.
325
Table 6. Experimental results of horizontal resolution for the 1 GHz antenna. The measurements
326
were made for two types of bars (wood and metal) at three distances (7, 91 and 147 cm). The results
327
are expressed in cm and in terms of the central wavelength of the antenna. The table includes the
328
theoretical estimations calculated from equations 3, 4 and 5, taking into account the effective
329
parameters of each antenna (Table 1).
330
Table 7. Experimental results of horizontal resolution for the 800 MHz antenna. The measurements
331
were made for two types of bars (wood and metal) at three distances (7, 91 and 147 cm). The
332
results are expressed in cm and in terms of the central wavelength of the antenna. The table includes
333
the theoretical estimations calculated from equations 3, 4 and 5, taking into account the effective
334
parameters of each antenna (Table 1).
335
Table 8. Experimental results of horizontal resolution for the 500 MHz antenna. The measurements
336
were made for two types of bars (wood and metal) at three distances (35, 143 and 196 cm). The
337
results are expressed in cm and in terms of the central wavelength of the antenna. The table includes
338
the theoretical estimations calculated from equations 3, 4 and 5, taking into account the effective
339
parameters of each antenna (Table 1).
AC CE P
TE
D
MA
NU
SC
RI
PT
311
ACCEPTED MANUSCRIPT
SC
RI
PT
_____________________________________ Antenna Effective Pulse Central Freq. Duration (ns) (MHz) _____________________________________ 1GHz 1.47 936 _____________________________________ 800 MHz 1.313 921 _____________________________________ 500 MHz 3.508 426 _____________________________________
TE
D
MA
NU
____________________________________ Distance Antenna – Bar (d) (cm) 16 (0.5λ) 63 (1.97λ) 143 (4.47λ) ________________________________ ___________________________________________ Wooden bars 20 (0.62λ) 20 (0.62λ) 20 (0.62λ) Vertical Resolution (∆V) (cm) _________________________________________________ 1GHz Metal bars 35 (1.1λ) 30 (0.94λ) 30(0.94λ) ___________________________________________________________________________
____________________________________ Distance Antenna – Bar (d) (cm) 16 (0.5λ) 74 (2.27λ) 119 (3.66λ) ________________________________ ___________________________________________ Wooden bars 20 (0.61λ) 20 (0.61λ) 20 (0.61λ) Vertical Resolution (∆V) (cm) _________________________________________________ 800 MHz Metal bars 35 (1.1λ) 30 (0.92λ) 30(0.92λ) ___________________________________________________________________________
AC CE P
340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392
___________________________________________ Distance Antenna – Bar (d) (cm) 10 (0.23λ) 85 (1.98λ) 185 (3.66λ) ________________________________ ___________________________________________ Wooden bars 20 (0.61λ) 20 (0.61λ) 20 (0.61λ) Vertical Resolution (∆V) (cm) _________________________________________________ 500MHz Metal bars 35 (1.1λ) 30 (0.92λ) 30(0.92λ) ___________________________________________________________________________
ACCEPTED MANUSCRIPT
SC
RI
PT
_______________________________ Theoretical Vertical Antenna Resolution (cm) (Eq 2) _______________________________ 1GHz 9.0 (0.28λ) _______________________________ 800 MHz 10.6 (0.33λ) _______________________________ 500 MHz 26.3 (0.61λ) _______________________________
TE
D
MA
NU
___________________________________________ Distance Antenna – Bar (d) (cm) 7 (0.22λ) 91 (2.8λ) 147 (4.6λ) ________________________________ ___________________________________________ Wooden bars 15 (0.47λ) 50 (1.57λ) 70 (2.18λ) Horizontal Resolut (∆H) (cm) _________________________________________________ 1 GHz Metal bars 20 (0.62λ) 50 (1.57λ) 70 (2.18λ) ___________________________________________________________________________ Equation 3 21.9 (0.68) 56.2 (1.57) 70.4 (2.2) Theoretical __________________________________________________ Horizontal Resolution (cm) Equation 4 25.8 (0.8λ) 144.7 (4.5λ) 223.8 (7λ) 1 GHz __________________________________________________ Equation 5 16.2 (0.5λ) 177 (5.5λ) 262 (8.2λ) ____________________________________________________________________________
AC CE P
393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444
___________________________________________ Distance Antenna – Bar (d) (cm) 7 (0.22λ) 91 (2.8λ) 147 (4.6λ) ________________________________ ___________________________________________ Wooden bars 15 (0.46λ) 55 (1.7λ) 75 (2.3λ) Horizontal Resolut (∆H) (cm) __________________________________________________ 800 MHz Metal bars 20 (0.61λ) 55 (1.7λ) 75 (2.3λ) ___________________________________________________________________________ Equation 3 22.2 (0.68 λ) 56.8 (1.74 λ) 71.1 (2.19 λ) Theoretical ___________________________________________________ Horizontal Resolution (cm) Equation 4 26.2 (0.8λ) 145 (4.46λ) 224.2 (6.9λ) 800 MHz ___________________________________________________ Equation 5 16.2 (0.5λ) 177 (5.47λ) 262 (8λ) ____________________________________________________________________________
ACCEPTED MANUSCRIPT
TE
D
MA
NU
SC
RI
PT
___________________________________________ Distance Antenna – Bar (d) (cm) 35 (0.81λ) 143 (3.32λ) 196 (4.56λ) ________________________________ ___________________________________________ Wooden bars 40 (0.93λ) 80 (1.86λ) 100 (2.32λ) Horizontal Resolut (∆H) (cm) _________________________________________________ 500 MHz Metal bars 50 (1.16λ) 80 (1.86λ) 100 (2.32λ) ___________________________________________________________________________ Equation 3 44.35 (λ) 81.3 (1.9 λ) 94.3 (2.2 λ) Theoretical __________________________________________________ Horizontal Resolution (cm) Equation 4 71 (1.65λ) 223.7 (5.2λ) 298.6 (6.95λ) 500 MHz __________________________________________________ Equation 5 76 (1.77λ) 257 (6λ) 328 (7.63λ) ____________________________________________________________________________
AC CE P
445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463
ACCEPTED MANUSCRIPT Fig 1
RI
PT
464
Fig 2
467 Fig 3
AC CE P
468
TE
D
MA
NU
466
SC
465
469
ACCEPTED MANUSCRIPT Fig 4
PT
470
SC
Fig 5
MA
NU
472
RI
471
AC CE P
475
Fig 6
TE
474
D
473
476 477
ACCEPTED MANUSCRIPT Fig 7
RI
PT
478
Fig 8
481 482 483
484
Fig 9
AC CE P
TE
D
MA
NU
480
SC
479
ACCEPTED MANUSCRIPT Fig 10
RI
PT
485
486
Fig 11
D
MA
NU
488
SC
487
491
Fig 12
AC CE P
490
TE
489
