I know that the size of the radiation box is at least quarter wavelength from the structure. However, I want to know is it a quarter wavelength of the frequency where the reflection coefficient is minimum (i.e. Fo) or from the lower frequency of the antenna BW where the reflection coefficient indicates -10 dB. I know this question was asked so many times before but I couldn't determine which of the answers is the correct one... Could anyone help me?
regards,
Eman,
Yes, whatever you're thinking is correct. that's depend upon your antenna size as well as sometimes on frequency, but normally we use size of radiation box is 6h+L and 6h+W.
Could you tell your specific problem so that i could help you.
All the best!
Smrity's formulae are right. Normally we consider very large size depending on type and size of antenna.
Thank you for your reply!
My design isnot microstrip based structure and i am confused about the size of the radiation box, is it a factor of the wavelength where the minimum reflection obtained or from F-lower in th bandwidth i.e. At -10 dB reflection?
You should choose smallest frequency (or highest wavelength between minimum reflection obtained and f lower in the bandwidth) for determine the size of radiation box.
Dear Eman Galal Mahmoud,
1. HFSS needs airbox to model free space radiation. A radiation boundary is used to emulate free space by truncating infinite free space to finite calculation domain. This minimize reflections from outer surfaces and ensures maximum absorption. This is very similar to an anechoic chamber.
2. For this, the distance from the radiator must be a minimum of λ/4 (or λ/2) for strong radiating surfaces. Here λ represents the wavelength for the minimum frequency used.
3. A distance of λ/4 from the radiating surface is taken for the reason that similar impedance mismatches can be cancelled at quarter wavelengths. This ensures that there are no reflected waves and thus the radiation boundary absorbs all the radiation.
4. Maximum absorption of energy occurs when the fields are perpendicular to the boundary.
Hope this helps!
Regards,
Suhas. D.
more than λ/4 distance of the resonating frequency from all the sides of the geometry can be used as radiation box dimensions. Mostly used when antenna is to be placed in far field.
I have a study on absorbing boundary condition for antenna's simulation and measurement. By means of PSO algortim, radiation box size is determined as 0.867λ at 1.5-3 GHz.
Lambda/4 is a minimal distance from the body of device. Better if placed somewhat far from, lambda/2 or more. So needed to avoid the near field absorption in radiation surface, and impact of boundary surface to calculating S-parameters, etc.
lambda / 4 distance is chosen, taking into account the resonance frequency of the antenna.
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