The practical magnitude of axial ratio for circular polarization can go upto 6 dB (0 dB
If you send circular or elliptical polarization RHCP or LHCP the opposite side can receive with orthogonal polarisation no less than -3 dB in any position H or V or Slant +-45°
RHCP to LHCP polarisation isolation is up to 25 dB currently it is 20 dB.
Sir Ducasse Jean-Claude,
Did you mean "RHEP to LHEP polarisation isolation is up to 25 dB currently it is 20 dB" ?
Thank you for your reply!
The circular polarization is of practical importance. The circular polarization of the left and right rotation forms an orthogonal basis. Elliptic polarization describes the reflected distorted wave. There are no waves in nature with pure circular or linear polarization. Polarization isolation in the orthogonal basis characterizes this degradation. Polarization isolation depends on a number of factors. To a greater extent, the design of the antenna affects the decoupling. In some antenna designs, the polarization isolation can be as high as 40 dB.
u[p to 20 (i.e. 26 db) is rather easy.Higher values are possible but maybe not very stable in practice.It all depends on the setup (microwave or. optical ) and the transmission medium which itself may be depolarizing.
@ Fritz Caspers and @Ducasse Jean-Claude Sir My Axial Ratio is from 12.5 db to 25dB. So i want to ask that is it circularly polarized?
and also in my simulation when i plot Gain and axial ratio then it shows both for adaptive passes. so can we take that value also of gain and AR?
hi, as you know according to data presented in the literature, when AR value is less than 3dB, we say that the polarization is CP. it means that one diameter of the ellipse of polarization is two times greater than the other diameter.So, i think that any value of AR which is greater than 3db can be considered as elliptical polarization.
Normally the definition for circular polarization is, that both axes of the ellipse are equal and the field components 90 out of phase...if they are in phase it linear polarized..this can be nicely visualized of a scope with x-y display (like for Lissajous Figures)
If your axial ratio is anything other than 1 (0dB) then your wave is elliptically polarised, but it is usually assumed that it is supposed to be circularly polarised and is referred to as circularly polarised, with the understanding that it is imperfectly circularly polarised, with the imperfection limit given. The limit gives the amount of cross-talk there will be between channels, or the transmit-receive isolation that can be achieved.
Sometimes elliptical polarizartion is what is actually required, in which case it is referred to as elliptical. A similar achievable rejection ratio will apply for elliptical polarization, with the added requirement to get the axes right as well, which is not needed for circular polarization.
thank you all of you for valuable answers. sir @Malcolm White i have also a question that can i measure AR on any angle or a particular angle (phi and theta)
The axial ratio can only be measured across the principal axes of the signal's polarization ellipse. If you measure at other axes you will not get the axial ratio. For instance, the axial ratio for linear polarization is infinite, but if you measure the axial ratio using linear polarizations at +/- 45 degrees to it then the two signals will be equal. Axial ratio is often measured using "spun linear", where the linear polarization of the measuring antenna is continuously rotated during the measurement. Then the maximum and minimum values can be observed, giving the axial ratio. If you can measure phase, then you can measure the axial ratio and phase difference between any any two orthogonal polarizations (linear, circular or elliptical) and use those to reconstruct the polarization of the original signal, and its axial ratio.
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