We are using the CST Studio Suite 2022 version. We are working on the Antennas - Time Domain section. The results we expect to obtain do not actually correspond to the simulation results.
CASE STUDY: We created the design of an antenna fed through two ports (PORT 1 and PORT 2). A DEFAULT signal is given as input for each port, the signal enters port 1 with phase 0° and the signal enters port 2 with phase 90°. By studying the Farfield at a given frequency we expect to obtain a Circular Polarization. The result we get is a linear polarization. That's very weird. We ask for technical support on this issue.
Do the two ports feed antennas with perpendicular polarizations? Is the length of both feeds from the port to the antenna the same?
Antennas such as the ports lenght are the same. Ports are placed perpendicularly each other.
Have you checked the fields into the antennas (using monitors) to see if they actually are 90 degrees out of phase in the simulation?
Have I check if the E field and H field in vectorial representation are orthogonal each other? Usually I did check the polarization through the Axial Ratio and till now it's at 40 dB (linear pol).
II wasn't referring to the E and H fields (electric and magnetic fields) being orthogonal to each other. They will be, in the far-field, by definition. If you ask for a electric field monitor you can see the electric field in the antenna and feed line at a moment in time. You can choose which phase to see, or animate the fields so you see them changing. Using this it is possible to see if the two feeds have electric fields peaking at the same place at the same time or whether they are a quarter cycle from each other.
Studying the electric field at a specific moment in time and a specific phase, in the proximity of the feed lines we spot a distribution that really seems a circular polarization. For our purposes, an EM wave has to be circularly polarized at a very long distance far from the antenna and not only in the proximity of the feeds lines. We explect to get an EM wave circularly polarized along a specific direction in the farfield (kR >>1).
You haven't answered my implied question, but I think you have said that the fields, in the same simulation, to the two identical linearly polarized antennas, are 90 degrees out of phase, as shown by the fields on the feed lines and ports.
Also, I think that you have said this:
The two antennas are 90 degrees rotated in space, and both the same distance along the axis pointing in the direction of the antenna beam, which is also the axis the rotation angle is measured about.
I can't see what can be going wrong.
Do the two antennas have the same aperture, or are they side-by-side. If they share an aperture, then the electric field directly in front of the aperture should be circularly polarized, too, and you should be able to see it rotating in the field monitor. The same is true of the magnetic field.
What is the antenna that you are modelling? Is it a waveguide antenna? Is there a built-in lag of 90 degrees already in the antenna, so that your extra 90 degrees puts it back to linear polarization?
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