| Contents |
Introduction
Model Description Simulation And Results |
References
Appendix - Files |
Thanks to Mansor Nakhkash of the
University of Liverpool
for providing this example.
Each antenna is loaded with four 170 ohm resistors which is nearly
equal to characteristic impedance of the transmission lines.
These resistors make the antennas broadband.
There is a metallic shield which minimizes the radiation at top and sides of
the antennas and directs the radiation toward the ground.
The antennas are held by a foam which fills the space inside the shield.
The shield is covered by a plastic case (in the model just the bottom section
of the case is considered).
The transmitting antenna is excited by a Gaussian pulse whose width
determines the center frequency of the received signal.
Model Description
The device contains two bow-tie antennas, one for transmitting and
one for receiving.
The transmitting antenna is driven by a pair of conductors attached
from above.
The receiving antenna has a similar transmission line, where the
return signal is measured.
|
The complete model.
The sources introduced in the transmitting line are in red, and the probes placed in the transmitting and receiving lines are in green. The outer metallic shield is in blue, and the plastic cover is in pink. A insulator protects the transmission lines from shorting to the metallic shield. |
|
With the metallic shield, foam packing, and plastic cover stripped away,
the inner conductors can be seen in blue and yellow.
The bowtie antennas are connected to the metallic shield via resistors on each corner. |
|
Bottom view, with the plastic cover removed. |
|
Signal on the input transmission line. The waveform shows both the input pulse and the reflection from the transmitting antenna. |
|
Signal on the receiving transmission line.
Good agreement was observed between the calculated results and experimental measurements. |
The same antenna model was run with several different multi-layered
mediums placed beneath the device, in addition to the homogeneous
reference model.
A 1-D inverse scattering method is used with the result of the
LC simulation to find the permittivity, conductivity and thickness
of layers of the mediums.
References
L. Peters JR., J.J. Daniels and J.D. Young, "Ground
Penetrating Radar as a Subsurface Environmental Sensing
Tool," Proc. IEEE, vol. 82, pp. 1802-1821, Dec. 1994.
Appendix - Files
Copyright © Cray Inc.
Maintained by Kevin Thomas (kjt@cray.com).
Last modified
Thu Jul 16 09:27:50 CDT 1998