What is relationship of scattering matrix parameters (Svv, shv, Svh, Svv) of material with the scattered rays at reached at prediction point after scattered from that material ?

Imran Haider_22350

I am trying to understand the roughness factor  for the two scattered rays (Ray2 and 3) which are shown in the attached picture.

All 03 Rays are interacting with the conductive guardrail (material properties given for finding Fresnel reflection coefficient)

 

01 Ray is reflected,  so roughness factor  =1,  and |R12| = 0.99, and Received power Pr(dbm) = -67dbm

02 Rays are scattered, Incident angle and scattering angles are calculated Pythagorean theorem.(Shown in the Attached picture)

Scattering matrix parameters for Guardrail also given    ,   

 How do I use  scattering matrix parameters to find roughness factor for Ray2. ?

 

Please help.

 

Regards

 

Imran

mvogel

This question has been answered through regular customer-support channels for the version that this customer is using. Kudos for searching in the User guide, by the way :-)

For all other readers: the scattering analysis in WinProp has been modernized in recent versions. Now it is based on the specification of typical surface roughness (in cm) by the user. Knowing the surface roughness and of course electromagnetic material properties and frequency, WinProp computes scattering in all directions. The user doesn't have to deal anymore with Svv, Shh, or the equations shown above.

Imran Haider_22350

Hi Dear

 

I am PhD Student at Zhejiang University China. I am using Winprop 2021.2 to 3D Ray Tracing, Fresnel Coefficients for interactions.

I have attached two pictures to explain the scenario i am simulating V2V scenario at only one time instant. Pls see attached 02 pictures. 

Ray1 and Ray 2 covered almost similar distance so Pathloss is both is almost same. However, Ray1 seems reflected at same angle as incident angle, so i assume that roughness factor for Ray 1 is 1. The Winprop Result for Ray1 is almost same as Calculated Result using Equations given in Winprop Guide 2021.

I have following query which need to clarfied for my research.
1) Roughness factor  = f(delta_h, incident angle , wavelength), Altair assistant (Jaehoon) told me that delta_h is specified in material properties as roughness which is used in Roughness factor calculation.  i have done received E-field and Power calculations scattered Ray 2 which suffers more loss due to Roughness factor for guardrail but Winprop results are far different than i have calculated using equations given in Winprop guide. Can you explain Why ????
Pls answer as soon as possible

regards

Imran

mvogel

Hello Imran,

Thanks for pointing out that you are using version 2021.2. That version uses the new scattering algorithm.

The equations in the WinProp guide are just about a material spreadsheet that is shipped with the examples in C:\Program Files\Altair\2021\help\winprop\examples\ExampleGuide_models\Example-A03-Database_Materials.zip. I think these equations help calculate by how much to reduce the reflection coeeficient when the surface is rough. For an upcoming version, we have adjusted the User guide to make more clear that these equations are just about that Excel spreadsheet. The new (better) scattering algorithm may not use the same equations.

In any case, I think I see where the confusion comes from. Based on the equations, you expect ray 2, the scattered ray, to be only a little weaker than ray 1 (reflection). Instead, you observe that WinProp predicts ray 2 to be MUCH weaker than ray 1.

What is really going on: ray 1 (reflection) WITH roughness is a little weaker than ray 1 without roughness. That is what those equations are about: the reflection coefficient of the reflected ray goes down a bit. The little power that is no longer going into specular reflection will become available for scattering. This little power is divided over thousands of scattered rays in many directions in 3D. One of the many scattered rays reaches the receiver. That is ray 2 (okay, it comes from a lightly different location, but you get the idea). Ray 2, being only one of many scattered rays, can only carry a small fraction of the little bit of power that has been taken away from the specular reflection.

By the way, I have obtained reasonable results for automotive radar simulations when I set the surface roughness to more than half a wavelength. Even for smooth cars, I exaggerate the surface roughness. If I don't do that, then the result depends too much on a few lucky reflections where the (flat) reflecting surface is oriented just right.