circular and dual polarization ?

read this http://en.wikipedia.org/wiki/Polariz...s:_plane_waves

you can look at circular polarization as sum of two linear vectors
some antennas can produce circular polarization. but you can
generate circular polarization by using two linear and orthogonal elements
with 90° phase shift between them.

pl

what about dual polarization

you can think of circular polarization as plasma noted.

some antennas can be fed in various orientations to create different polarizations. this assumes that reasonable swr, desired mode of operation and isolation can be achieved when doing this. this is in fact done in some antennas and then combined in quadrature to form circular polarization. crossed dipoles, horn antennas so on.

however if you didnt combine those different feeding points then you would have dual polarization, because the antenna is fed in seperate locations and for each of those locations provides needed swr, isolation and radiation parameters.

hi,

in simple terms,

The dual polarization is both E-phi and E-theta components are equal in amplitude and phase may not be equal. If the phase of the both the components are equal, then they are circularly polarized.

equal amplitude but not equal phase. e-phi and e-theta must be 90 degrees out of phase to construct circular polarization.

equal phase would be dual linear and anything not equal 90 would be elliptical (cp being this special case of elliptical polarization)

http://www.kathrein-scala.com/tech_b...lPolarized.pdf

Now a days Base station antennas are dual polarised antennas whose antenna elements are placed diagonally(± 45deg) and the angle between two elements should be 90deg(I dont know the reason why it should be 90 deg?)

Circular polarization(CP)- Two electric fields of equal amplitude with 90 deg out of Phase.

CP antenna receives both linear and CP fields but former with 3dB less.

C.P is achieved by different ways using
branch line couplers,
feeding along the diagonal of the patch,
corner truncating patch antenna

Regards,
Balaguru.