Calculating Radar Cross Section

In summary, the conversation revolves around the topic of using ray tracing to compute radar cross section (RCS) using geometrical optics or some form of it. The method involves casting rays from an emitting object and finding where they intersect a surface, reflecting them and seeing if they intersect the emitter again. This process is iterated until convergence is achieved. The conversation also discusses the use of Monte Carlo integrators and the challenges of predicting RCS for complex real-world objects. The expert suggests using Physical Optics instead of geometrical optics and mentions the radiation equation as a better approach for integrating the ray field. There is also a mention of using GTD/UTD (geometrical theory of diffraction/uniform theory of diffraction) and its limitations
  • #1
erkokite
39
0
I am trying to write a program to numerically calculate RCS using geometrical optics (or some form of it). Basically my idea was to cast a bunch of rays from an emitting object (in my code it is a 1 m^2 plate), find where they intersect a surface, reflect the rays off of this surface and see if they intersect the emitter again (monostatic RCS).

The rays take the form:
[tex]u=\vec{A}e^{iks}[/tex], where [tex]k=\lambda/c[/tex], and is a vector amplitude representing the electric field, and s is path length.

Basically I sum all outgoing rays:

[tex]E_{transmit}=\sum{u_{transmit}}[/tex]

and
incoming rays:

[tex]E_{receive}=\sum{u_{receive}}[/tex]

Basically I have a Monte Carlo integrator spit out rays randomly, which are added to [tex]E_{transmit}[/tex], specularly reflected over geometry and added to [tex]E_{receive}[/tex] if they bounce back and hit the emitter/detector geometry. This iterates until [tex]E_{receive}[/tex] converges (also at least 1000 runs are performed). Now, I know it converges because I can run the program over and over again and get roughly the same answers with less and less variation depending upon my acceptable error value.

After I have a value for [tex]E_{receive}[/tex], I then take:

[tex]RCS=(|E_{receive}|^2/|E_{transmit}|^2)[/tex]

Now, when all outgoing rays are reflected back to the transmitter, I get a value of 1.0. This was my test case for a 1 m^2 flat plate parallel to the emitter, with all rays traveling along the z axis- basically perfect directivity in a sense. If I let rays scatter along a hemisphere and attenuate them based on pointing error, I get a lesser value, but still a sane value. This makes sense to me. However, I have yet to figure out how exactly to convert this square meters.

Aerospaceweb.org gives an RCS equation of:

[tex]4\pi a^2b^2/\lambda^2[/tex]

This of course, does not match my results, but I think that's because I am quantifying my RCS much differently.

So in short, my questions are:

Does my method seem to make any sort of rational sense? (My training was in aerospace engineering, not electrical engineering, so I don't know these things)

How do I go from received E field magnitude to an RCS in square meters?

Thanks.
 
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  • #2
You are attempting to use ray tracing to compute an integral by Monte Carlo. This is a really bad way to compute radar cross section unless you capture the rays and use the radiation equation to integrate the ray field. Even then the answers will be terribly inacurate. You want to use Physical Optics, not geometrical optics. If you really insist on using GO, look into using GTD/UTD (geometrical theory of diffraction/uniform theory of diffraction). There are good programs for this developed at Ohio state.
 
  • #3
One problem in predicting RCS is the irregularity and complexity of real objects. In my previous job we obtained measurements of the RCS of several different cars on a turntable, full circle at 1 degree increments. The variation in RCS was in some cases more than 10 dB in adjacent bins.

With this in mind you should consider the utility of your results, if you intend to detect complex real-world objects.

My basic point is, is there really any benefit to having a tool for estimating RCS, compared to measuring it?
 
  • #4
Antiphon said:
You are attempting to use ray tracing to compute an integral by Monte Carlo. This is a really bad way to compute radar cross section unless you capture the rays and use the radiation equation to integrate the ray field. Even then the answers will be terribly inacurate. You want to use Physical Optics, not geometrical optics. If you really insist on using GO, look into using GTD/UTD (geometrical theory of diffraction/uniform theory of diffraction). There are good programs for this developed at Ohio state.

I am looking at switching to GTD/UTD, and eventually figuring out a way to add traveling/creeping waves, but first I want to get the basics working. So I wanted to get pure specular reflection working first, then adding diffuse scattering due to surface roughness and edge diffraction then corner diffraction.

You are right that it is terribly inaccurate and inefficient and a poor way of going about things, but I figure, Monte Carlo is easily parallelizable and also this seemed like a rather intuitive way of going about things for me, so this is just the way I coded it. I'm mainly doing it purely as a learning process to learn about RCS physics as well as Monte Carlo techniques, not as a practical tool.

I thought about using PO, but the problem with this is that doesn't handle curved surfaces well, but I suppose if I am using GO, accuracy is probably not my main concern anyway. :D

What is this radiation equation you speak of?

Thanks for your help.

Ken Freeman said:
One problem in predicting RCS is the irregularity and complexity of real objects. In my previous job we obtained measurements of the RCS of several different cars on a turntable, full circle at 1 degree increments. The variation in RCS was in some cases more than 10 dB in adjacent bins.

With this in mind you should consider the utility of your results, if you intend to detect complex real-world objects.

My basic point is, is there really any benefit to having a tool for estimating RCS, compared to measuring it?

I just want to predict simple objects, as a learning exercise, like spheres, and plates, perhaps some very approximate simple aircraft shapes. I would like to estimate these things as I don't have access to an RCS range or fabrication equipment or the money or time to fabricate and measure these things.
 
  • #5
Ken Freeman said:
In my previous job we obtained measurements of the RCS of several different cars on a turntable, full circle at 1 degree increments.

Hello Freeman,

I know this is a old post, but I'm looking on the web for results for measurements for RCS of cars (up to have an idea on the range on various angles, mainly for perpendicular incident wave).

Have you an idea of where could I find such information ?

Thanks a lot !

Antoine
 

1. What is Radar Cross Section (RCS)?

Radar Cross Section (RCS) is a measure of how detectable an object is by radar. It is the effective area of a target that intercepts an amount of incident power and reflects it back to the radar receiver.

2. How is RCS calculated?

RCS is calculated using radar range equation, which takes into account the transmitted power, wavelength, target size, and target reflectivity. It is also affected by the target's shape, orientation, and materials.

3. What is the unit of RCS?

RCS is typically measured in square meters (m^2) or decibels relative to a square meter (dBsm). The higher the RCS value, the more detectable the target is by radar.

4. How is RCS used in radar systems?

RCS is an important parameter in radar systems as it helps in target detection, tracking, and identification. By knowing the RCS of a target, radar operators can determine the range, speed, and direction of the target.

5. What factors can influence RCS values?

Several factors can affect RCS values, including the target's size, shape, and materials. Additionally, the target's orientation, surface roughness, and frequency of the radar signal can also impact RCS values.

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