axial ratio linear polarization

hi,

Does any one of you have any information about the calculation of axial ratio for examining the dual linear polarization of antenna pattern. should it be near to 1 for a good dual linearly plarized microstrip antenna.

Thanks for your attention.

abhi

stange your use of the term "calculation".
For my opinion, A.R. is calculated by Computer simulators, (like GRASP, HFSS, CST, Feko etc)
A.R. is measured by people.
After a measurement AR is simply the ratio.

Axial Ratio is a term that is typically used with respect to Circular - not Linear - Polarization. For a good dual-LP antenna, Axial Ratio will be very high, say > 35 dB, since LP axial ratio is essentially the cross-pol discrimination (XPD). For a good dual-CP antenna, Axial Ratio should be very low, say < 1 dB, since CP axial ratio is essentially the polarization purity.

Note: a 1 dB AR => 24.4 dB CP XPD; a 2 dB AR => 18.8 dB CP XPD.

Modern Antenna Design, 2d. ed. by Milligan (Wiley Publ.) has a very good section on antenna polarization.

Typically the XPD of CP antennas is less than that of LP antennas, but LP systems require polarization alignment and are more susceptible to atmospheric depolarization effects (e.g. Faraday rotation).

Cheers,
eckypting

if using The Tree antennas method, you have to measure S21 vertical and horizontal components and for Linearly polarized antenna is simply |S21H|/|S21V|
which is >> 1

and for circularly pol antenna is as follows
if LHCP
S21L=1/2*(S21H+jS21V)
S21R=1/2*(S21H-jS21V)
if RHCP
S21L=1/2*(S21H-jS21V)
S21R=1/2*(S21H+jS21V)

and the axial ratio=abs(|S21R|+|S21L|)/(|S21R|-|S21L|) shuold be around 1db

hope this helps

Hi all, i got some question regard the polarization of EM wave
AR< 3d ; consider as circular polarization?
AR<-10 db; consider linear polarization?
AR=? ; consider ellpitical polarization?