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Antenna models
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This section provides some example models of antennas. Each example comes with an input file which you can download and run.
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Wire dipole antenna model
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=========================
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**INFO ON THIS MODEL IN PROGRESS**
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:download:`antenna_wire_dipole_fs.in <../../user_models/antenna_wire_dipole_fs.in>`
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This example demonstrates a model of a half-wavelength wire dipole antenna in free space. The length of the dipole is 150mm with a diameter of 6mm, and a 1mm gap between the arms.
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.. literalinclude:: ../../user_models/antenna_wire_dipole_fs.in
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:language: none
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:linenos:
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.. figure:: images/antenna_wire_dipole.png
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:width: 600 px
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FDTD geometry mesh showing a wire dipole antenna model.
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The antenna is fed using the ``#tranmission_line`` command. The one-dimensional transmission line model virtually attaches to the dipole at the gap between the arms. The antenna has an input impedance (:math:`Z_0`) of 73 Ohms specified in the ``#tranmission_line`` command. The transmission line uses a Gaussian waveform with a centre frequency of 1GHz.
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Results
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-------
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.. _antenna_wire_dipole_fs_tl_params:
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.. figure:: images/antenna_wire_dipole_fs_tl_params.png
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Time and frequency domain plots of the incident and reflected (scattered) voltages in the transmission line.
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.. _antenna_wire_dipole_fs_ant_params:
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.. figure:: images/antenna_wire_dipole_fs_ant_params.png
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s11 parameter and input impedance (resistance and reactance) of the antenna.
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Bowtie antenna model
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====================
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:download:`antenna_MALA_1200_fs.in <../../user_models/antenna_MALA_1200_fs.in>`
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This example demonstrates how to use one of the built-in antenna models in a simulation. Using a model of an antenna rather than a simple source, such as a Hertzian dipole, can improve the accuracy of the results of a simulation for many situations. It is especially important when the target is in the near-field of the antenna and there are complex interactions between the antenna and the environment. The simulation uses the model of an antenna similar to a MALA 1.2GHz antenna.
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.. literalinclude:: ../../user_models/antenna_MALA_1200_fs.in
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:language: none
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:linenos:
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.. figure:: images/antenna_MALA_1200.png
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:width: 600 px
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FDTD geometry mesh showing an antenna model similar to a MALA 1.2GHz antenna (skid removed for illustrative purposes).
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The antenna model is loaded from a Python module and inserted into the input file just like another geometry command. The arguments for the ``antenna_like_MALA_1200`` function specify its (x, y, z) location as 0.132m, 0.095m, 0.100m using a 1mm spatial resolution. In this example the antenna is the only object in the model, i.e. the antenna is in free space. When the simulation is run two geometry files for the antenna are produced along with an output file which contains a single receiver (the antenna output). The antenna bowties are aligned with the y axis so the output is the y component of the electric field. More information can be found in the :ref:`Python section <python>`.
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Results
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:numref:`antenna_MALA_1200_fs_results` shows the time history of the electric and magnetic field components from the receiver bowtie of the antenna model. The antenna bowties are aligned with the y axis so the output will be the Ey component of the electric field.
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.. _antenna_MALA_1200_fs_results:
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.. figure:: images/antenna_MALA_1200_fs_results.png
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Field outputs from the receiver bowtie of a model of an antenna similar to a MALA 1.2GHz antenna.
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B-scan with a bowtie antenna model
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==================================
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:download:`GSSI_1500_cylinder_Bscan.in <../../user_models/GSSI_1500_cylinder_Bscan.in>`
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This example demonstrates how to create a B-scan with an antenna model. The scenario is purposely simple to illustrate the method. A metal cylinder of diameter 20mm is buried in a dielectric half-space which has a relative permittivity of six. The simulation uses the model of an antenna similar to a GSSI 1.5GHz antenna.
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.. literalinclude:: ../../user_models/GSSI_1500_cylinder_Bscan.in
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:language: none
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:linenos:
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.. figure:: images/GSSI_1500_cylinder.png
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:width: 600 px
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FDTD geometry mesh showing a metal cylinder buried in a half-space and an antenna model similar to a GSSI 1.5GHz antenna.
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The antenna must be moved to a new position for every single A-scan (trace) in the B-scan. In this example the B-scan distance will be 270mm with a trace every 5mm, so 54 model runs will be required.
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.. code-block:: none
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python -m gprMax GSSI_1500_cylinder_Bscan.in -n 54
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The total number of runs for a model as well as the number of the current run of the model are stored and can be accessed in Python as ``number_model_runs`` and ``current_model_run``. The ``current_model_run`` can be used to move the position of the antenna for every run of the model as shown in Line 13. The antenna will be moved 5mm in the x direction for every new run of the model.
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Results
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:numref:`GSSI_1500_cylinder_Bscan_results` shows the B-scan (image of the Ey field). As expected a hyperbolic response is present from the metal cylinder.
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.. _GSSI_1500_cylinder_Bscan_results:
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.. figure:: images/GSSI_1500_cylinder_Bscan_results.png
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:width: 800px
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B-scan of model of a metal cylinder buried in a dielectric half-space with a model of an antenna similar to a GSSI 1.5GHz antenna.
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