Radar Cross Section simulation with CST

[Unconscious]

I'm trying to understand how CST measures the RCS of an object. If not specified by me, it gives me (with a very brief simulation even for complex objects) graphs, both 3D and 2D, entitled 'Bistatic RCS'. With this wording I think that there is an antenna in a different direction than the one from which I send the plane wave incident on the target, which receives the reflected wave. However, I never specified the presence of a second antenna, nor did I tell it where it is.
What is it showing me? I do not understand.
It also shows me another number that it calls 'Total RCS' that I don't even understand what it means.
Help, please?

Thank you.

 

[berkeman]

Can you post some screenshots of your geometry and the simulation results?

https://www.3ds.com/products-servic...=cst.com&utm_medium=301&utm_campaign=products
https://www.microwavejournal.com/articles/15768-cst-design-studio

 

[Unconscious]

I can't post geometry, but I can post screenshots describing my procedure.

I have a plane wave excitation with the following setup:

where the angles are parametrized:

and a field monitor for RCS:

This is the Integral Equation Solver setup:

Note the 'monostatic RCS sweep' active, which 'Properties...' are:

So, if I don't make comprehension errors, I'm asking CST to do 4 simulations for theta = 0, 60, 120, 180.

...I continue to the next message because I can't attach more than 5 images at a time...

 

[Unconscious]

Launching the simulation with the settings described above I get the following results:

In particular, in the 'Farfields' folder, the subfolder named '(f=9) theta=...' contains monostatic RCS results. For example, choosing 'Theta' under this subfolder, I see:

where I don't understand why I find written, besides phi = 0 (which is the reference plane that I asked for), also phi = 180 (without points, apart from those strange red lines that go straight into the origin).

Choosing instead 'Theta' from the subfolder 'farfield (f = 9) [pw]' ([pw] stands for...?), we get this graph:

As you can see it is titled 'Bistatic Scattering RCS', I don't understand what he has calculated and who asked him to do this type of calculation too.

 

[tech99]

Bistatic means separate TX and RX antennas, not in the same position.

 

[Unconscious]

I know, the question is not about the mean of ‘Bistatic’.
The question is about why CST shows these results when I only asked ‘Monostatic’. In addition, I don’t know who is the receiving antenna that CST considers in the bistatic RCS calculus.

 

[Unconscious]

If anyone can reply, I also ask what does the results 'theta phase' and 'phi phase' means in a CST Radar Cross Section simulation.
I don't think that they are the phase difference between the sent plane wave and the received plane wave, because:

1. I have not said to CST what is the distance between the antenna (the same for TX and RX in monostatic RCS calculations) and the target under test;
2. the Radar Cross Section is defined as a ratio of real quantities (absolute values of the incident and the received fields), so no phase is present in the definition.

Thanks in advance.

 

[Tom.G]

RTFM (Read the Fine Manual) or try Google.

https://www.google.com/search&q=radar+cross+section+using+cst

 

[OCR]

Lol. . .

(Read the Fine Manual)

Uh-huh. . . and I'm the FNG (Fairly New Guy). .

.

 

[Unconscious]

I already viewed that video, no info are present about the phase.
Same things in the documentation, in the ‘help’ section.

I can’t understand the OCR message, even if it seems to me to be a message of mockery.

 

[Tom.G]

Unfortunately I have not used the CST package and am only passingly familiar with radar. From the video I would guess that theta is angular position of the target relative to the antenna.

Theta and phi are briefly shown at time 2:20 in the video, with a hint of what they are.


At this point I should bow out because I lack adequate knowledge to be of help.
With that, I will turn this back over to @berkeman. If needed, either he or I can request help from other staff. Let us know if needed.

Sorry I couldn't help more!
Tom

 

[OCR]

. . . a message of mockery.

No, not mockery. . . just friendly banter between Tom G and myself.Carry on. . . .
.

 

[Unconscious]

I would guess that theta is angular position of the target relative to the antenna.

Yes, in general CST has a reference cartesian frame, from which one can switch in a spherical frame with $(r,\theta,\phi)$ variables.
In a RCS problem in CST, one sends a plane wave on a target (a 3D draw made by the user). The direction of such a plane wave is dictated by the angles $\theta_0$ (angle between the propagation direction and z-axis) and $\phi_0$ (angle between the projection on xy plane of the plane wave propagation vector and the x axis).
From this, the simulation result that I expect is a function of the couples of angles $(\theta_0, \phi_0)$, whose arrival domain contains all RCS values in $\mathrm{m}^2$ (or $\mathrm{dBm}^2$), that CST calls 'abs RCS' . I can also restrict the simulation results fixing one angle, for example $\phi=0$, and making the other moving.

This is, instead, what I obtain:

In addition to 'abs', in the results folder there are many other things, whose significance is obscure for me (no mention on them was made in the CST help guide). In particular there are 'theta phase' and 'phi phase', that CST shows as:

An hypothesis could be that these two results are the phase difference between the sent plane wave and the received plane wave, but this sounds strange for me for the reasons exposed in #10.

 

[Unconscious]

If needed, either he or I can request help from other staff. Let us know if needed.

If it were possible to ask for extra support on this thing, I would really appreciate it.
In particular about the significance of the results called 'Theta Phase' and 'Phi Phase'.

Thank you in any case.

 

[Klystron]

My experience with radar is 40 years out-of-date but I may be able to help with a few terms and concepts. I have zero experience with your design software.

PW in radar context usually refers to pulse width. Practical radar signals are pulsed to concentrate power within the pulse-forming-network PFN and to synchronize transmitters TX and receivers RX. Perhaps your software expects or infers a pulse width parameter?

Early radar used continuous wave CW through omni or mono-pole antennae or simple strung lines such as the UK used in the Battle of Britain. Synchronized pulsed systems protect receivers while transmitting the pulse, then "listen" between pulses.

The "red lines" resemble splines connecting the points where the radar signal has been detected (measured). I see dots at the transmitter TX antenna location, at the far field diffraction (or RF reflector, repeater, or another receiver) area, and behind the TX at your RX antenna.

Have you also plotted near field diffraction? This article may help.

Since this is a simulation, assuming a pulsed system, can you TX and RX from the same location for simplicity?

That is about all I have for now except that pulse width affects your radar mile but I have to think how PW affects cross section. I tend to relate RCS to antenna design thus, wavelength.

 

[Klystron]

This diagram provides a flat depiction of near and far -field EMF.

https://en.wikipedia.org/wiki/Near_and_far_field#/media/File:FarNearFields-USP-4998112-1.svg
This excerpt from wikipedia describes a reasonable explication of your antenna pattern noting that the "red lines" in your simulation probably represent curves (splines).

The equations describing the fields created about the antenna can be simplified by assuming a large separation and dropping all terms that provide only minor contributions to the final field. These simplified distributions have been termed the "far field" and usually have the property that the angular distribution of energy does not change with distance, although the energy levels still vary with distance and time. Such an angular energy distribution is usually termed an antenna pattern.

This excerpt explains why far-field representations are common even though near-field effects become critical close to the antenna.

Note that, by the principle of reciprocity, the pattern observed when a particular antenna is transmitting is identical to the pattern measured when the same antenna is used for reception. Typically one finds simple relations describing the antenna far-field patterns, often involving trigonometric functions or at worst Fourier or Hankel transform relationships between the antenna current distributions and the observed far-field patterns. While far-field simplifications are very useful in engineering calculations, this does not mean the near-field functions cannot be calculated, especially using modern computer techniques. An examination of how the near fields form about an antenna structure can give great insight into the operations of such devices.

In my experience hyperbolic trigonometric functions adequately model simplified radar signal while I visualize far-field emf encompassed by a toroid since near-field predominates close to the antenna. I can ping an engineer expert in dialectric materials and/or a superb mathematician/geometer, depending on how you wish to proceed.