as you said:"the efficiency is smaller than 1 and so G must be lower than D" and it is clearly correct, also you said:"I find the gain is smaller than the directivity" and this is correct too, so what is you problem exactly ?!
Possible reasons:
1. in ur simulation model, metal loss is considered
2. mesh on the radiation boundary is too coarse, therefore the far field calculation is not accurate.
If You kwon, HFSS, and other softwares those solve the maxwell equations using numerical method, are dividing the Antenna and other mediums to diffrent pieses and will consider the wave on each pieces constant and fix. So if the length (area) of each picecs is long this consideration is wrong and you will receive wrong analysis and result.
solution is considering low area for each pices, thet is means increse the density of meshes, as asdfaaa Said.
Just want you to confirm that you want the airbox to be lambda/4 larger than the "MINIMUM LAMBDA".
I think it should be read: "lambda/4 larger than the HIGHEST LAMBDA (corresponding to the lowest frequency).
Am I correct ? The airbox has to be LARGE engough.
Thanks.
oxo
Even if you mesh the radiation boundary very well, you can get numerical errors that will lead to gain > directivity. I've seen radiation efficiencies slightly greater than one from HFSS antenna models that are adequately meshed.
I believe this stems from the fact that the FEM solves for the E-fields directly and then calculates H-fields and the currents and far-field quantities from H-fields. So some small numerical error may be difficult to remove when using this method.
Possible reasons:
1. in ur simulation model, metal loss is considered
I don't understand what it means...
If I consider metal loss I have efficiency=Rrad/(Rrad+Rloss) <1. And no problem exists...
In the case of pec efficiency = 100% and so I would have G=D...
Isn't it right?
Possible reasons:
1. in ur simulation model, metal loss is considered
I don't understand what it means...
If I consider metal loss I have efficiency=Rrad/(Rrad+Rloss) <1. And no problem exists...
In the case of pec efficiency = 100% and so I would have G=D...
Isn't it right?