Toolboxes is a sub-package where useful Python modules contributed by users are stored.

GPR Antenna Patterns

Information

Author/Contact: Craig Warren (craig.warren@northumbria.ac.uk), Northumbria University, UK

License: Creative Commons Attribution-ShareAlike 4.0 International License

Attribution/cite: Warren, C., Giannopoulos, A. (2016). Characterisation of a Ground Penetrating Radar Antenna in Lossless Homogeneous and Lossy Heterogeneous Environments. Signal Processing (http://dx.doi.org/10.1016/j.sigpro.2016.04.010)

The package contains scripts to calculate, process, and visualise finite-radius field-intensity patterns from simulations containing models of GPR antennas. Electric or magnetic field components are sampled by receiver circles around the antenna and integrated over the time record. This makes the method useful for antennas operating across an air–ground interface or in heterogeneous ground, where a conventional homogeneous-background near-to-far-field transformation is not applicable.

These outputs are not NTFF radiation patterns, gain, or directivity. They show the angular distribution of a time-integrated tangential-field intensity at the requested observation radii. Patterns at several radii are useful for showing how the field distribution evolves through the near-field and radiating regions.

Warning

Although the principles of calculating and visualising field-intensity patterns are straightforward, this package should be used with care. The package:

• Does not calculate a conventional single-frequency far-field pattern. It uses a time-integrated field-intensity measure at each angle and radius; see http://dx.doi.org/10.1016/j.jappgeo.2013.08.001.

• Requires receiver circles large enough to contain all desired observation radii, which can make the FDTD domain computationally demanding.

• Must not be interpreted as antenna gain or directivity. Use the NTFF antenna outputs for those quantities when the antenna and integration surface are entirely in a homogeneous background.

Package contents

• initial_save.py selects the explicitly identified pattern receivers, calculates the time-integrated field intensity, and stores the patterns and their metadata in a NumPy .npz file.

• plot_fields.py plots the processed patterns. It should be used after the data has been processed by initial_save.py.

The package has been designed to work with the input file found in the examples directory:

• antenna_like_GSSI_1500_patterns.py includes a model similar to a GSSI 1.5 GHz antenna and receiver circles for its principal E- or H-plane. It also writes a JSON metadata file used by the processing script.

How to use the package

Run the E-plane example on CUDA device zero:

python examples/gpr/antennas/gssi_1500/antenna_like_GSSI_1500_patterns.py --pattern E --gpu 0

The default 1 mm model is intended for producing the final pattern. For a quicker workflow check, the antenna model also supports a 2 mm grid:

python examples/gpr/antennas/gssi_1500/antenna_like_GSSI_1500_patterns.py --pattern E --resolution 0.002 --gpu 0

After the simulation, process the HDF5 receiver outputs. The matching JSON metadata file is found automatically:

python -m gprMax.toolboxes.AntennaPatterns.initial_save examples/gpr/antennas/gssi_1500/antenna_like_GSSI_1500_patterns.h5

Finally, create the polar plot:

python -m gprMax.toolboxes.AntennaPatterns.plot_fields examples/gpr/antennas/gssi_1500/antenna_like_GSSI_1500_patterns.npz

Use --pattern H for the H-plane. The model stores the radii, angles, pattern plane, material properties, and antenna origin in the metadata file, so the processing and plotting scripts do not have to be edited to match the model.

Tip

Plot limits and output filenames can be changed using the command-line options of plot_fields.py without re-processing the HDF5 output.

Fig. 59 Example of the E-plane pattern from a simulation containing an antenna model similar to a GSSI 1.5 GHz antenna over a homogeneous, lossless half-space with a relative permittivity of five.