Use "open add space boundary" for antenna simulation.

Dear Dalam,

For antennas operating in free space, I would use the "open add space" boundary condition. This boundary setup is essential if you need to record the far-field pattern. Furthermore, if you are interested in the electric field in the radiating near-field (Fresnel) region (Modern Antenna Handbook by Balanis) and not only the reactive near-field, then, I would manually extend the added space in the advanced settings of the "open add space"  boundary conditions by a distance of 2D^2/lambda, where D is the diameter of your antenna and lambda is the free space wavelength. After you setup the boundary condition correctly, then, use an electric field monitor at the desired frequency.

I hope you find this information useful.

Thank you.

Robert Salama.

Hello!

As Mr. Robert is suggested about " open add space" boundary condition, I do agree with him. For radiation of antenna into free space this boundary condition is well suited. There, you can easily add specific fields like electric and magnetic at every walls and open end with properties and easy to monitor fields characteristic for your operating or resonant frequencies.

Thanks,

As you have mentioned you are designing in CST so no issues for defining the boundary. CST automatically calculates the boundary dimensions as per the design.