MoM efficiency problems
To take into account the mismatch, we talk about "Antenna effeciency" and not about "Radiating effeciency", so the antenna effeciency is difined as the ration between the radiated power and the available power in the RF gen.
My question is:
Both IE3D (Zeland) and Momentum (Ansoft) EM Solvers, cannot compute the radiating effeciency of antenna. For example, when we are in the simple case of an antenna within a perfect dielectric, the radiating effeciency must to be close to 1 (100%) if we do not consider the metal loss. However IE3D or Momentum give strange values about 0.6. Is it an issue due to MoM algorithm implemented with these two softwares?
Antenna effeciency is also decided the match coefficient. and the other: the loss of dielectric and conductor.
In the radiation,we interesting the power leak out the antenna.(total power=the leak+resonate)
Just in my opinion.
I guess the same term means different thing for different people
Can you tell us:
1. what is the antenna you simulated to get the 0.6 "radiation efficiency"?
2. what kind of input impedance or S11 you are obtaining?
1. what is the antenna you simulated to get the 0.6 "radiation efficiency"?
only include the leaky power.
2. what kind of input impedance or S11 you are obtaining?
nomaly we use 50ohm system to simulate.
It's a dipole antenna. The radiating effeciency is not related to the matching level, it's defined as the ratio between the radiated power and the injected power into the antenna.
But if we want to calculate the antenna effeciency, we need to know the matching level.
The dielectric considered here, is supposed free of losses, so the radiating effeciency must to be close to one, and even equal to 1 if we suppose that the wires are perfect conductors. However with IE3D or Momentum it is not the the case.
Don't know about your exact configuration, but if it is not a wrong setup, it may well be a strong excitation of surface waves that re-radiate at the edges and distort your pattern. It is strange because Zeland always tend to exagerate the radiating efficiency (not rare 100%) and does not account at all for surface waves. Momentum does and issues a warning.
So, without more information it is difficult to provide you a more than a guess.
regards,
cheng
can surface waves cause that much difference? 1.0 vs 0.6?
It is very likely that the project is not setup correctly. In other words, the codes did not calculate what you expect them to do.
Radiation efficiency is not related to the input matching , to calculate it you should calculate the surface current losses plus the losses due to metal-air interface (consider the antenna VSWR). it would be better to use FDTD simulator beause the error in MoM is much higher in this case.
Most of standard antennas have a pre-calculated values of radiation efficiency , these values doen't change signficantlly in most cases.
the term radiation efficiency has been clarified several times, so it is not the problem here. The question is how the strange answer 0.6 come about, and the s11 might give us a clue as to what happened.
Most people would agree that MoM would do a much better job in modeling non-perfect conductor and dielectric loss than FDTD does.
I still don't have any answer for this issue. Do you think that MoM algo neglict part of the radiation eff when we change the permittivity?
Loucy, my answer is yes. You can bet the surface waves might completely destroy the pattern. In my early days with patches (many years ago) I suffered a lot and had to tweak the design a lot before aleviating this. So, the answer of your question is yes, it is possible. But on the other hand as I mentioned, Zeland does not find the poles in the integrands (the surface waves modes) and makes no difference with or without. But the interesting part is that both tools show 0.6
I am also confused because the fellow mentioned Momentum (Ansoft). There is no such tool as you know, so we better have mor einfor before offering anything than just a guess.
regards,
cheng
To the fellow with the problem.
Unless you disclose more (if you are allowed) we shall be of very limited use here. The choise rests with you;)
Oh! sorry, I apologize, it's Momentum Agilent and not Ansoft like mentioned.
However, it seems that MoM algo implemented with IE3D and Momentum do not take into account the radiated power coming by the edges of the structure. You must know that both these two EM solvers, considerthe XY plane as infinite plane and hence may that's why they do not compute the radiated enrgy coming from the edges??? is it possible?
thx
IE3D's efficiency calculation is quite accurate from our test. Normally, it does yield good results with few exceptions. However, when you are modeling antennas in layere dielectrics, you will never get any value close to 100% due to the surface waves. Surface waves decay differently from radiation and it is not included in far field calculaiton. If your ground plane and substrates are large enough, the surface waves will eventually become dissipated. Then, the IE3D calculated efficiency should be quite accurate. If the ground plane and substrates are not large, then the surface waves will bounced back or leave the dielectrics at the edges of the substrates and become radiated field. In such a case, the infinite substrate model on IE3D will predict lower efficiency. However, you can try the finite dielectric modeling on the IE3D 10.1. With finite dielectric modeling, you normally should get an efficiency close to 100% if there is no other loss.