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The polarization of an antenna is the orientation of the transmitted (or received) electric field (E field). The optimum polarization for a system depends on the polarization of other antennas in the system. An infinite number of polarizations exist but the most common are linear and circular. For a linear antenna three possibilities generally are seen vertical, horizontal and slant linear. It is important to match linear polarizations for transmit and receive sites. A linear polarization mismatch can result in up to a 20 dB loss (for cross-linear polarization).
Circular polarization is generally given as right hand circular polarization (RHCP) or left hand circular polarization (LHCP). To determine the polarization of a circular antenna, use the right hand rule. Point the thumb of your right hand in the direction of propagation and curl your fingers. If your fingers point in the direction of propagation, the antenna is RHCP (otherwise it is LHCP). Polarization mismatch loss for circular antennas can also be up to 20 dB (for opposite sense polarization).
vfone, a credit for your explanation about polarization. I was thinking a lot about an answer but your explanation is splendid. I have an additional question about polarization. Let´s say we have to micro_strip antennas with circular polarisations, one for recieving and the other for transmitting . To achive reception, do both have to be RHCP or LHCP ? Can there be one with LHCP and the other with RHCP ? I disregard reception due to reflections.
And to danesh, i really recommend a basic regarding antenna desig by Balanis named ' Antenna Theory Analysis and Design '.
in order to have good polarization match you need to have the same polarization in both antennas. Otherwise you only measure the crosspolarization isolation between them.
The vfone's explanation is excellent but is regarding the EM Field only.
Practically, to recognize what kind of polarization transmits (or receive) your antenna, please look at the attached picture and follow the concept of "retarded axis".
Note: the vfone's explanation follow the IEEE definition (the Kraus definition), it's adopted in TLC, and in general in radio science. Note that it's opposite to the definition used in Optical Phisics.
agree with habib83, any book on antennas MUST include a polarization chapter (or at least a summary of concepts) which will help danesh to clarify his ideas. particularly I recommend Krauss, but I am a fan of him so my opinion is partial.
in the meantime find attached a chapter of the hollis (antenna measurement) book. I found it somewhere in the hyperspace, I'm afraid I didn't boormarked the site. If somebody is interested I got two other chapters ( 6 on antenna measurement theory and 8 on antenna gain measurement).
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