Could any one please inform which formula should I use for the calculation of the airbox dimension and What happens if the dimension varies ?
i think it depends upon what kind of radiation pattern for transmit and receive the antenna would make. the size should be approximately for near field formula which is D^2/4lambda. D is the diameter or aperture of the antenna.
In case of using "radiation" boundary condition, the radiation box need to be at least (lambda0/4) from the edges of the design. Where (lambda0) is calculated relevant to the minimum simulation frequency.
However, in the case of using "perfect matched layer" boundary condition, the radiation box need to be at least (lambda0/10) from the edges of the design.
In case of antennas the radiation box should defined as L+lambda/2, W+lambda/2, H+Lambda/2... Where the L, W, H are the substrate length width and thickness respectively. box should be lambda/4 distance away from the all the outer faces of Substrate.
Basically I have faced so many problems in this dimensions of airbox dear....but it also depend on which port you have assigned to your antenna dear...wave port oR lumped..after that i come to the conclusion that on the feed also it depends...
So let me know which antenna and feed you are design for it?
There are 3 radiation boundaries in HFSS. I believe you refer to the commonly used one called ABC. This radiation boundary should be placed at a distance of lambda/4 from a strong radiating side and lambda/8 from a weakly radiating side. If you have have a strong radiator, like a directive antenna array, it is recommended to use PML. You can get a size that works for any antenna, it depends on the angle of incidence of the fields on the radiation boundary.
Dear Umair and Zinal, there should be no relation between the excitation port and the radiation boundary. If you observe this issue, this means that you are not exciting your structure properly.
I think the radiation pattern should be measured at far field distance which is given by 2D^2/lambda0, where D is maximum dimension of antenna and lambda0 is free space wavelength. So you can make your box as large as the far field dimension. If box is too large, then you can minimize the dimension of box. In that case if your antenna has the broad side radiation then the distance between antenna surface and top of the box (+z direction) should be greater than 2D^2/lambda0. The diemsion of box in +x, -x, +y & -y direction and also in -z direction need not to be same as far field dimension. In that case simulation time can be reduced.
Most of the time if you take at least lambda0/4 from all sides of your structure it could give a reasonable answer...
Wriddhi, the far field calculation is different. The radiation boundary condition is an absorbing boundary condition made to absorb the fields at the interface between the background (which is PEC) and the air volume, or in other words it is an advanced impedance boundary condition. To calculate the far field, you do not have to use the radiation boundary to perform the calculation. Actually it is recommended to create another surface closer to the antenna to calculate the far fields.
we are always creating radiation box, at least, lambda0/4 from all sides of antenna structure bkz we are calculating all the parameter at far field. my question is why greater than or equal to lambda0/4?
Ashish, it is not because of the far field calculation. The radiation boundary is an absorbing boundary condition to reduce the reflection of the fields from the PEC background. When you increase the distance, the accuracy become better because the reflection gets reduced.
To Ibrahim,
Apart from this boundary condition, I would like to know in any substrate (say FR4), what ever the feed or ground plane we are using we should use 3D box with very less height or should use rectangular sheet ( and then assigning perfect E boundary).
Kindly suggest me which is correct and perfect method ?
Thanking You.
Sounik Kiran
If the thickness mater, then you should include it in the simulation. If it doesn't affect the performance, then there is no need to account for it. If you dont know, I suggest that you try both of the approaches and compare the results.
As suggested by many others, it should be between (lambda0)/2 to (lambda0/4). If you define more than that also no problem. But, computational time will increase. In fact, you will get more or less same results.
One more point is, the radiation box dimensions does not affect majorly on your return loss performance characteristics. The radiation box is only for radiation results.
As the dimensions of the radiation box are higher then, the reflections are lower from the radiation box towards the antenna. If the dimensions are more than lamda0/4, the reflections are negligible.
Well, it is quite interesting to find so many arguments and replies here about the radiation boundary... I would like to share my experience with the software!...
I experimented with resonant half wavelenght (0.475lambda ) dipole antenna with different dimentions of radiation boundary(Cylindrical) and in each case I observed input impedance of the dipole which was not the same ... the cases were ...
1. radiation boundary placed at lambda/10 and lambda/4 apart from the tips and sides of the dipole respectively.
2.radiation boundary placed at lambda/4and lambda/4 apart from the tips and sides of the dipole respectively.
3.radiation boundary placed at lambda/2 and lambda/2 apart from the tips and sides of the dipole respectively.
And in each time I observed different impedance which should not be like that as per majority of answers here... I am still looking for any reason for such a change !!
Or is there any bug from my side??
A radiation surface does not have to be spherical, but it must be exposed to the background, convex with regard to the radiation source, and located at least a quarter wavelength from the radiating source. In some cases, the radiation boundary may be located closer than a one-quarter wavelength, such as portions of the radiation boundary where little radiated energy is expected.
(p 4-3 of the attached file)
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