Default behavior of CST importer is to create a dual pol beam

[dannyjacobs]

On import of a single pol or feed beam the rotate_pol option sets whether to create an opposite polarization beam by rotating by 90 degrees. The default behavior is rotate_pol = True.

This became a problem when studying cross-coupling beams imported with the yaml methods, eg here.

This was hidden a bit by the rendering of the function call in readthedocs which shows the default value for this option as None. Things that would help here would be to have an explicit tutorial on importing CST beams and to somehow have the actual defaults show up in the function call.

The current solution for importing dual pol beams stored in the HERA-Beams repo is to downselect the "True" polarization in each file and then concatenate the two together.

B05 = UVBeam()
B06 = UVBeam()
B05.read_beamfits('NF_CrossCouplingBeams/NF_HERA-Dipole_ccbeam_port05_E-field.fits')
B06.read_beamfits('NF_CrossCouplingBeams/NF_HERA-Dipole_ccbeam_port06_E-field.fits')
B05.select(feeds=['x'],inplace=True)
B06.select(feeds=['y'],inplace=True)
DUAL_POL_BEAM = B05 + B06