Checking polarization of antenna

[itzikhaim]

Dear all!

How can I measure the polarization of antenna near field pattern ?
In matter of fact, the type of polar. is only interested for me (Circular, Elliptic, Linear).

Thanks in advanced!

 

[jiripolivka]

With a real antenna you can feed it with several mW at the operation frequency from a signal generator, and use a half/wave dipole with a detector diode in it as a detector of polarization.
Holding the dipole in hand on antenna axis and detector connected to a millivoltmeter, you should turn the dipole on antenna axis; if antenna radiates a linearly-polarized wave, the mV meter will indicate a round maximum and a sharp minimum. This test also will give you the correct polarization plane.
If your antenna radiates a circularly-polarized wave, the detector response will stay almost constant on the mV meter while you rotate the dipole.
To find out if your antenna radiates a left or right hand circular polarization, you should then make two small helical antennas , one with RHC, the other with LHC, and install a diode detector at its output (between the helix and a small reflector). Your mVmeter should respond with a higher voltage for the correct circular polarization.
You do not need to make really half-wavelength dipoles if your antenna is specified for a longer wavelength; the method will work , too, only you would have possibly use a higher RF power from the signal generator to get a good reading on the mV meter.

 

[vfone]

Now depends in what kind of near-field you are. For example in Reactive Near field the Electric-E and Magnetic-H fields are not orthogonal, and polarization is not a meaningful parameter.
Myself, I would go in the far field to measure the polarization of the antenna.