What's the best simulating method for antenna: FEM or MoM ?

Hi everybody!

How do you think, what is the best simulating software for antennas (pratch) - i have HFSS - based on finite element method and ensemble, based on method of moments. Both methods are similar, but may be one of tehm will be most accurate and usefull!

Regards!

Re: FEM or MoM (Ansoft)

for my part, I don't find HFSS very accurate

Re: FEM or MoM (Ansoft)

pepino said:

Hi everybody!
Both methods are similar, but may be one of tehm will be most accurate and usefull!
Regards!

Click to expand...

For p@tch antennas, I will certainly prefer MoM. BTW the two methods have a whole lot of diifference. They are not similar as you might think.

-svarun

Re: FEM or MoM (Ansoft)

BTW the two methods have a whole lot of diifference. They are not similar as you might think.

Click to expand...

Dear Sir, I will disagree with your statement. MoM is modifcation of FEM. But the reasone of my post was to clarify what method is the best for resonant srtuctures as p@tch antennas. If somebody has an experience, please let's make a comment!

Re: FEM or MoM (Ansoft)

if ur application is a patch antenna try the mom for fast result and be aware to use full wave mom for aaccuracy.it is preffered for planar application
if you need mor accurate result use the brut force method FEM , but this take much time in simulation.
I hope that declare in some how

Re: FEM or MoM (Ansoft)

FEM and MoM are completely different techniques. I have spent 22 years developing MoM. If I were to start working FEM, almost all of my MoM knowledge would be of no use.

For non-planar antennas, use volume meshing tools like FEM (Ansoft) or FIT (finite integration technique, similar to FDTD) CST, or one of several FDTD tools. In my opinion, CST is likely to be best for many problems, that is why my company decided to represent CST in US and Canada some years ago.

If your antenna is planar, best to use MoM. MoM meshes only the surface of the metal of your circuit. Ansoft Ensemble (now part of HFSS I am told), Agilent Momentum, and Zeland IE3D are the tools of choice there. You will find any one of those three tools will be 10X to 1000X faster than volume meshers. To get an idea of accuracy, look at the resulting current distribution. The correct current distribution has high current on all sharp edges and the current distribution is smooth everywhere. MoM tools give much better current distributions than FEM, etc., in addition to being much much faster for planar structures.

In my opinion, IE3D is a bit faster than Momentum, but Momentum appears to be a bit more accurate. My opinion is based on results for microwave circuits, not for antennas. Different people are likely to have different opinions.

Some people think that FEM gives more accurate answers than MoM for planar circuits. Perhaps this is because FEM takes sooooo much longer. This is totally wrong, as even just one brief look at the current distributions will tell you instantly.

One problem with MoM is that the substrate goes to infinity. If that is significant, then you have to use a volume meshing tool, it is no longer a planar problem.

I work for Sonnet. our MoM tool is for shielded circuits, but antennas can be done with some care, be sure to read the manual on antenna analysis carefully.

Re: FEM or MoM (Ansoft)


Please check the above message...even for this simple structure, HFSS gives inaccurate results. On the other hand MWS is quite accurate...I have experimentally confirmed this.

FEM or MoM (Ansoft)

Hi, James:

Don't always say IE3D is less accurate. Do you know that IE3D was chosen as the choice of 2.5D EM simulator by the whole Raytheon in 1999? Do you know that IE3D was rated as the most accurate one in modeling spiral inductors among all the EM simulators Motorola tested in 2003, where other simulators include Sonnet EM and Agilent Momentum. Do you know that IE3D was also chosen as by the Broadcom as the best tool in modeling RFIC in 1998?

Re: FEM or MoM (Ansoft)

Hi Jian -- That is my opinion based on a number cases I have seen users do on both tools. (If that is not my opinion, please tell me what my opinion is. :wink: ) I acknowledge that your opinion is different from mine, and that is 100% A-OK, and thank you for sharing it with us. I'm sure many others have opinions different from mine too, and they are very welcome to post those opinions as well (actually, I espeically like hearing opinions that differ from mine, it is a chance to learn something new). After all, this is the good old USA (this comment applies to Jian and myself, many other countries share similar values too)! We take strength in diversity of opinions and in many other ways.

I am open to changing my opinion based on good hard data, feel free to post or suggest any IE3D/Momentum comparisons you like (I'm sure I can find someone willing to run a few tests for me). If you can get good solid data posted (or even just show it to me privately if you prefer) I will be very happy to change my opinion. But it will take data, not statements about who happens to like a particluar tool (we can all make statements like that).

As far as people purchasing either IE3D or Momentum for their unshielded MoM needs, my main interest is to see they get the tool that is best for them. Any information you can provide to help make that decision better is most welcome. (This same offer is open to those who are convinced that Momentum is superior to IE3D, too.) Right now, I am convinced that IE3D is consistently a bit faster than Momentum. If you can convince me that IE3D is also consistently more accurate than Momentum, I won't hesitate to point all unshielded MoM customers for whom speed and accuracy are the primary concerns in your direction and away from Momentum. Makes absolutely no difference to my bottom line. As it stands right now with what I know, I have to point out that both tools have thier relative advantages.

See you next week at the show.

BTW, do you agree with my comments on FEM vs. MoM?

FEM or MoM (Ansoft)

Hi, James:

I think you understand the following fact very: Simulation accuracy is really dependent upon how the tools are being used and what types of structures we are simulating. Even the same structure and the same person simulating it, depending upon the settings, the accuracy can be different.

I think it is unfair to give a general statement in a public domain discussion about your competitor is less accurate in a general sense. Such statements can be very misleading.

Don't you agree with my comments about it?

Thanks!

Re: FEM or MoM (Ansoft)

pepino said:

BTW the two methods have a whole lot of diifference. They are not similar as you might think.

Click to expand...

Dear Sir, I will disagree with your statement. MoM is modifcation of FEM. But the reasone of my post was to clarify what method is the best for resonant srtuctures as p@tch antennas. If somebody has an experience, please let's make a comment!

Click to expand...

I understand that there the following fundamental differences between MoM and FEM. FEM solves for the fields while MoM solves for the surface current density. MoM incorporates radiation condition automatically due to its formulation. FEM requires a radiation box with artificial material to apply radiation condition. MoM borrows from FEM in the area of meshing (triangular mesh elements for planar structures in MoM vs tetrahedral mesh for volumetric elements and triangular mesh elements for planar structures in FEM) but meshing is not EM !!

The similarities of course are there in that both are frequency domain solvers and both use basis functions for imterpolation and both use matrix inversion. Please point out if there are any fundamental similarities.

Regarding IE3D, both Dr Rautio and Dr Jian are well known and well respected in the microwave community and I feel it does not look nice to fight in the public. Any experimental verifications of the statements would be most enlightening for all of us.

FEM or MoM (Ansoft)

Hi, Svarun:

Thank you very much. I agree with you. As a vendor, we should not say bad things about competitors in a public domain discussion. We have sticked to it unless we are attached. Thanks!

Re: FEM or MoM (Ansoft)

Hi Jian -- If you can bring some data supporting your position to MTT, I would be very happy to see it. If convincing, I will recommend you over Momentum in any and all areas (including and not lmited to accuarcy) that you or your customers provide persuasive data for. I'm serious about that. I am entirely open to the possibility you have consistently better accuracy than Momentum or are superior to Momentum in other areas, all you (or any of your users) have to do is show me some good solid data to that effect.

If desired, I will be glad to keep your specific results confidential and not discuss specifics with Agilent or others. Of course, the same offer goes for Agilent, if they like. Basically, I think you have a good product, it is just there are other good products out there too.

Keep in mind that all softwares have weaknesses. I will not hesitate to point out, when important, those weaknesses for any and all softwares as well. Does not matter who the software comes from (including our own software), I can point out good things, and I can point out bad things. If it is just a subjective opinion, I will point that out too. It is very important to be able to do this kind of thing, especially on a forum such as this. It is also important to keep an open mind and be willing to change those opinions when presented with the appropriate facts and data. I think the worst thing that could happen is that people refrain from expressing serious opinions, because then there is no discussion of those opinions. Good opinions will not be heard. Bad opinions will remain unchanged. Feel free to change my opinion. If I only stated my opinion privately, you would have no chance to challenge my opinion with facts and data. Now you can. And I will listen closely and carefully. Convince me.

Certainly I am aware of the problems with validation that you mention, and I view any data I see with these potential problems in mind. Even so, with care, a convincing case can be made. If you are willing to do that, you can get me on your side for unshielded MoM. Really. I have absolutely no special attachement to Agilent, or to any other unshielded MoM vendor.

Also, I feel you have more advantages than just faster analysis, and some of them are very significant. I can list what those advantages are as well, but then I would also feel compelled to list other advantages Momentum has too. Both tools have significant strengths.

I think we would all be pleased to hear your opinion on FEM for planar circuits if you would share that with us. I think this is an area where our opinions might be similar, but I am not sure.

Hi svarun -- Your comments on FEM and MoM theory I agree with completely. Well stated.

FEM or MoM (Ansoft)

Hi, James: I don't mind what you say about other company's products. However, as a competitor, you keep saying "IE3D is less accurate" in a general sense and in a public domain discussion is offending to Zeland and to all the users who make the choice to use IE3D. I consider it as a misleading statement. As I mentioned, different simulators are differnt. Accuracy can not be concluded in a simple statement or a simple example. There are so many things involved. You can find many examples one simulator is more accurate than the other or in the opposite ways. I respect any people who respect me. I don't mind any person to say bad thing against me and our products privately. If it is true, we wil learn it and improve our products to meet the nees of the customers. I think many of our customers have gave us feedback. We learn from them and make our products better and better. Thanks!

Re: FEM or MoM (Ansoft)

why do you just mention about the accuracy? what makes a software a "good software" for customers (I am a customer) is not just the accuracy or just the speed. We look for "ease of use". We look for "good support". We look for consistent "development". We look for incorporation of "custom features". There are many factors that determines our decision.

Re: FEM or MoM (Ansoft)

I agree wtih Irfan a lot. When we first delve into EM simulation, which by itself is a huge area, we look for ease of use and support. Here CST Microwave Studio scores very well. I must add that some of my lab members and myself initially found that Jian was very helpful with any problems they faced with IE3D. Congrats on that front.

We should give credit also in public so that it serves as a stimulus tho the vendors.

Re: FEM or MoM (Ansoft)

svarun said:

I agree wtih Irfan a lot. When we first delve into EM simulation, which by itself is a huge area, we look for ease of use and support. Here CST Microwave Studio scores very well. I must add that some of my lab members and myself initially found that Jian was very helpful with any problems they faced with IE3D. Congrats on that front.

We should give credit also in public so that it serves as a stimulus tho the vendors.

Click to expand...

Friends,

signing Irfan's and svarun's statements.
We are customers of MWS and IE3D and there's almost no problem that we aren't able to solve.
Thanks Jian for your very kind support, even here in forum!!!

Re: FEM or MoM (Ansoft)

Hi Jian -- Please carefully notice that I did not say your product is less accurate than Momentum. I said that it is my opinion that Mommentum is a bit more accurate and that undoubtedly others have different opinions (i.e., I am stating my opinion is not necessarily correct, very important point). The reason I am careful to state that that is my opinion is because it is impossible to be completely certain for the exact reasons you state. I am very open to seeing data that will change my opinion. Many people on this forum have stated their opinions on which softwares are best for specific problems. I do not compete with you for unshielded MoM problems, so I think it is reasonable that I can state my opinion too.

Just for some background, there were two occasions (1988 and 1993) when Agilent (then HP) caused extreme distress for me and my company. (I will describe those situations to you privately if you are interested.) However, I will not allow that to influence my technical opinion. If I think Momentum has a strong point, I will say so. If I think IE3D has a strong point, I will say so. But if you give me half a chance to endorse IE3D for unshielded MoM with specific data for specific reasons, I would actually like to do it. Let's get together at MTT for a bit discuss it if you like, but please, I need more than generalitiies to modify my technical opinions. Specific data is useful, or even just suggestions for tests that I might get someone to run are also helpful. I do have customers who ask me which is better, IE3D or Momentum, I often give an answer in favor of you (see below), but only if the data that I have seen supports, in my opinion, the conclusion I make. I will not make a conclusion against anyone, Agilent or otherwise, just because we had some difficult times in the past.

Hi irfan1 and svarun -- Actually I have been talking about accuracy and speed, not just accuracy. But you are both correct, there are many points to consider in deciding what software is best, and the answer for different people and different situations is different. I will just give a few examples below of what I might tell a prospective user who needs an unshielded MoM tool and Sonnet, being a shielded tool, is not the best answer.

1) A customer has ADS and integration is important. Consider Momentum. IE3D and Ensemble are not integrated into ADS.
2) A customer has AWR and integration is important. Consider IE3D. Momentum and Ensemble are not integrated into AWR.
3) A customer already has HFSS. See if Ensemble can meet your needs. Ensemble is already part of HFSS, no extra cost.
4) A customer is new to EM and can benefit from support being provided durectly by the developer. Consider IE3D. (After all, how many other founder/developers do you see giving personallized support on this forum!)
5) It is important to the customer that the developer still be with the company, and will stay with the company for future enhancements. Consider IE3D.
6) Detailed technical support is needed in both Chinese and English. Clearly IE3D.
7) The largest feature set is needed. Again, clearly IE3D.

Notice that in all the above cases, accuracy is likely to be a secondary issue, as long as there is enough accuracy to get the job done. When I talk about IE3D vs. Momentum, I consider both to have sufficient accuracy and speed to get most jobs done, it is just that I view one to be "a bit" better in accuracy, and the other "a bit" better in speed. Is this really a problem?

Notice that I have compromised my integrity in the above list, it is heavily weighted in IE3D's favor, but every point listed is 100% reflective of my opinion (others may have different opinions).

The reason I have not broadened the discussion to all these points before, is think about how complicated this thread will get if we have half a dozen people all actively stating serious but diverse opinions on all these points....! It is a very multi-dimensional situation.

FEM or MoM (Ansoft)

Thank you to all of you! I appreciate all your feedback. We will do our best to solve our customer's problems and incorporate whatever features we need to and can implement to address our customer's needs. For me, I don't want to attack and I don't want to give comments to any of our competitors. I believe that any such statement can be biasing and it is unfair to other vendors and to the designers. Thank you very much!

Re: FEM or MoM (Ansoft)

I thank both Dr Rautio and Dr Jian for their comments. There were a lot of things to take from them. I think they have shown (at least me) how things work beyond the academics. I appeal to both not to be overcome by any sort of emotion and to continue posting useful stuff in this forum. We need guys like you both !!

Finally thanks to pepino too for having started this thread probably not knowing the turns it would take !!
Eirp, Is it time to draw curtains on this discussion ?

-svarun