It depends upon the kind of antenna that is required in the application.
Circularly polarized antennas will have an axial ratio is 1 (0 dB). A perfectly linearly polarised antenna has an infinite. An elliptically polarised antenna has an axial ratio greater than 1.
If you're looking for details on AR for circularly polarised antennas, then this thread may prove helpful.
https://www.researchgate.net/post/How_do_I_measure_axial_ratio_of_the_antenna
obviously ranged from 0 dB (pure CP) to inf. dB (pure LP)
practically CP is considered elliptical polarized as you can't get 0 dB (i think that is ideal case for CP). It considered axial ratio below 3 dB for antenna to be said it is CP antenna
The axial ratio depicts following iformations
1) It conveys the alignment of between Tx and Rx antenna for better reception
2) It conveys the cross polar effect for other users
3) It distinguishes channels and provides the idea of interference
4) In case of mobile application, it can provide the idea about effect of yaw and rolling
For linearly polarised antenna AR is infinite, meaning E field either in horizontal or in vertical polarization (maybe a small value in either one when another is infinite in real world case).
If CP, then it need to be below 3dB, basically its a ratio of vertical and horizontal.
How to know this?,
1. antenna software able to give you the axial ratio for single frequency versus angle, if you sweeping for large bandwidth, then look how to set this in software,
2. radiation pattern co polar and cross polar, and if you able to look at your E field it will rotate on antenna structure.
3. For practical measurement, if you receiving antenna is LP, then you must have a similar gain in different angle for transmitting antenna.
hope its help.
Axial ratio defines how close the polarization is circular. It is the ratio of E fields in orthogonal planes (say Ex and Ey). When these fields are equal the ratio is 1 (or 0dB) (i.e., Ex and Ey are radius of a circle). However, it is difficult to obtain ideal value (1 or 0dB), up to 3dB (Ex>Ey or vice versa for elliptical case) is being considered as acceptable value of axial ratio.
Axial ratio for circular polarization is 1. For horizontal polarization it is 0 and for vertical polarization it's infinity.
axial ratio depicts the extent of circular polarization of an antenna. The closer the value of axial ratio towards 0dB the antenna will be much circular polarized.
AR is the ratio of the magnitudes of the major and minor axis defined by E field vector.
AR=0dB means an ideal CP. However it's difficult to achieve this ideal value, values less than 3dB are considered acceptable for Axial ratio.
Le rapport axial est le rapport des composantes orthogonales d'un champ E. Un champ polarisé circulairement est composé de deux composantes de champ E orthogonales d'amplitude égale (et déphasées de 90 degrés). Parce que les composants sont de même amplitude, le rapport axial est de 1 (ou 0 dB).
Le rapport axial d'une ellipse est supérieur à 1 (> 0 dB). Le rapport axial pour la polarisation linéaire pure est infini, car les composantes orthogonales du champ sont nulles.
Les rapports axiaux sont souvent indiqués pour les antennes dans lesquelles la polarisation souhaitée est circulaire. La valeur idéale du rapport axial pour les champs à polarisation circulaire est de 0 dB. De plus, le rapport axial a tendance à se dégrader en s'éloignant du faisceau principal d'une antenne, de sorte que le rapport axial peut être indiqué dans une fiche technique (fiche technique) d'une antenne comme suit: "Rapport axial:
The ideal value of Axial Ratio is 1 in linear scale ( ie 0dB), but in reality we can not find 0dB, so if we obtain an Axial Ratio of antenna less than 3dB, so we can say that is acceptable.
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