copolarisation

hi,

can anyone help me in understanding copolarisation and crosspolarisation of an antenna clearly

Simply speaking co-polarization mean "That polarization which the antenna is intended to radiate" and cross mean "That polarization which the antenna is intended to radiate".

For a clear look plese see the attaced tutorials
:D

Sorry man:

Cross Polariztion mean "In a specified plane containing the reference polarization ellipse, the polarization orthogonal to a specified reference polarization". The reference polarization is usually the co-polarization."

Both of the definiton are taken from " IEEE Standard Definitions of Terms for Antennas, IEEE Std 145-1983."

Read these 2 papers

At the antenna connector you may receive (or transmit) only one wave polarization. (linaer or circular). The 90° far polarizzation is generally unwanted.
Cross-polarizzation (Xpol) is the 90° far, unwanted polarizzation.
Co-polar (Copol) is the wanted polarization.
I.e. if a standard antenna TX a vertical pol. , in far field region, when you RX a Vertical one, you RX the Copol, while if you try to receive Horrizontal, you'll receive the Xpol.

Many definitions exists for Xpol. For my knowledge, the most widely adopted is the Ludwing's one.

A good antenna has Xpol less than -30dB