Discussion Forum

Dear all,

I am using COMSOL 5.1 to simulate antennas in different mediums. I am a novice in antenna design and in antenna simulation. I would like to use COMSOL to see how the radiation characteristics (resonance frequency, input impedance, far field pattern...) evolve with the dielectric properties of the medium.

I started focusing on the resonance frequency using very simple models (e.g. the dipole antenna from the tutorial) in free space. I built the model with the tutorial and tried to add the eigenfrequency study. The eigenfrequencies are always complex. The real part should indicate the resonance frequency and the harmonics in my opinion. From the reference manual, I understood that the imaginary part expresses the losses in the model. I have two questions about this:

1. Found eigenfrequencies exhibit often resonance, not only of the antenna but of the whole structure (truncating sphere). I am only interested in the resonance of the antenna itself since it is supposed to be modeled in a infinite space. Is it possible to specify this? How can I get rid of these parasitic solution? It prevents me from finding the solutions I am really interested in.

2. I usually take the option to search the eigenfrequencies around the frequency that should be the lowest resonating frequency (speed light divided by wavelength for an half wavelength antenna) and look for the frequency that are the closer in absolute value. Even with those choices, I do not even find the main frequency and the frequencies that are found are very close to each other (could not be harmonics of each other). Can you see any issue with these selections?

I tried to find tutorials and explanations on the eigenfrequency study for the RF module but did not manage to find helpful information (except some in the RF module user guide). If you think about something that could be useful and that I did not find, can indicate it to me? It would be very nice.

Thanks already for the help you could give!

Aurélie