Question about simulating mirror effect of radar with different wavelength

[Dongyu Du]

Hello! I recently started to use gprMax for my work about analyzing the mirror effect of the radar with different wavelength as shown in the following:  

To achieve this, I would like to confirm whether the gprMax supports the following functions:

1. Whether Tx antenna can emit the signal forward a specific spatial direction just like a laser/ the real radar

2. If I want to compare the mirror effect with different wavelength, do I need to define the wavelength dependent material first? If so, does gprMax support this kink of material?

I appreciate all the help I can get on this. Thanks in advance! 

[Antonis Giannopoulos]

Hi Dongyu,

I would say mostly that is a "no" but with some exceptions that depend on the details of what you are trying to do. In order to get a directive source "like a laser" you need to actually simulate the directive antenna that produces this type of radiation. For microwaves most likely a Horn but there can be others (helical antennas, etc.). This can be done in FDTD and gprMax but as you realise the model will most likely need to be in 3D (there can be some exceptions!) and rather large if the distance from the antenna to the wall is substantial. The other way is to generate a plane wave (assuming that the source is far away). The current version of gprMax does not do this as it is not common in GPR but the next version in development (level branch) will have a plane wave source that works only for targets embedded in a homogenous space and not for half space problems. This could be an issue simulating a response from an infinite wall. Simulating a spatially localised directive source like a "gaussian beam" is not something that can be done at the moment. In principle one can spatially weight properly a plane wave source and achieve this but and in FDTD it has been done and there are papers about this and obviously commercial tools that do that. gprMax does not implement such a source but we would love to have such additions. 

If you are looking for something ready made to do what you need then it is more likely that sadly gprMax is not your answer except if you really want to model the antenna part and go down that road. If you have seen papers that do what you want using FDTD and gprMax does not have that functionality you can use it a base to add and develop that functionality if you like programming and Python and contribute to the code.

Hope this helps

Antonis

[Dongyu Du]

Thanks for your detailed answer!

I'll try to use pyfptp package to achieve the directional wave. There is a line source in pyfptp which can be use to control the propagation direction. Looking forward to the next version of gprMax!