Normally, to obtain good radiation characterstics, the dimensions in all sides of the radiation box has to be a quarter of the wave length of your operating frequency.
According to the hfss documentation, the edges of the radiating box are located at lambda/3 from the nearest antenna size. Since version 18 you can automatically create a box using the "Create open region" function
The radiation box in HFSS, also referred to as an air box, plays a crucial role in antenna simulations by absorbing outgoing electromagnetic waves. Its dimensions are critical to ensure accurate results without affecting the antenna's behavior. Here's how to calculate them:
Minimum Size:
A common rule of thumb is to set the radiation box size to at least a quarter wavelength (λ/4) larger than the biggest radiating edge of your antenna in all directions at the lowest operating frequency. This ensures minimal reflection from the box boundaries.
Calculation:
For example, if your antenna has a width of 5 cm and the lowest operating frequency is 2 GHz, then:
- λ = (3 x 10^8 meters/second) / (2 x 10^9 Hz) = 0.15 meters (15 cm)
- Minimum width of radiation box = 5 cm + (λ/4) = 5 cm + (15 cm / 4) = 7.5 cm
Additional Considerations:
- While λ/4 is a good starting point, a larger box won't affect the results significantly, only increasing simulation time.
- You can use software features to visualize field intensity and ensure it's minimal at the box boundaries.
- If unsure, start with a large box and gradually decrease its size in small increments while monitoring key parameters like S-parameters (scattering parameters) for minimal changes. This iterative approach helps determine the optimal size for your specific antenna design.
By following these guidelines and considering the additional factors, you can ensure accurate antenna simulations in HFSS with appropriate radiation box dimensions.
Right-click and select "Create Open Region". It will automatically create an appropriate-sized radiation box.
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