why not use circular polarization antenna in wireless comm.?

[wusen]

No matter in GSM or CDMA or PHS..., In Base Station, linear or dual-polar antenna are using ,while in handheld terminals always using linear-polar.
Why doesnot use circular-ploar antenna to minimize the polarization mismatch?
thanks!

 

[salem_sajid]

Re: why not use circular polarization antenna in wireless co

From whatever little knowledge i have(little knowledge is a dangerous thing) i ll try to give u a point to think. Certain kind of polarizations are more suited to certain aaplications. Circular polarization is genrally used where we are trying to overcome the interference as its more resistant to it. One classical example is the missile warheads or other tracking radars or some sort of those appliances where we want to avoid any interference but of course its more complex than horizental or vertical polarization.

So i would say not all kinds of polarizations are best for a particular application.

Its just my opnion.

Regards
Ess ESS

 

[vfone]

Re: why not use circular polarization antenna in wireless co

Circularly polarized antennas are usually more costly than linear polarized types and hard to be implemented in mobiles.
Circular polarization has been used to minimize the multipath propagation.
Linear polarized antennas will work with circularly polarized antennas and vice versa; there will be up to a 3 dB loss in signal strength, but multipath-fading can affect more than this.
Usually Earth-to-Satellite mobiles use circular polarized antennas.

 

[biff44]

Re: why not use circular polarization antenna in wireless co

Well, sometimes they are. FM broadcast stations in the US are often elliptically polarized, ie part horizontal and part vertically polarized. This improves reception in the city.

 

[toonafishy]

Re: why not use circular polarization antenna in wireless co

A circular polarized wave and a linear polarized wave will not eliminate the mismatch. It will reduce the mismatch. It will be better than a horizontal versus a vertical. But it will never be as good as a vertical and a vertical. Antennas on cells phones are vertical, base station are vertical, its the best match (unless you make phone calls laying down!).

 

[flatulent]

Re: why not use circular polarization antenna in wireless co

Prior to 802.11 there was a successful company in the US that used the 5 GHz band and two oppositely circularly polarized antennas. Since a circular wave reverses direction on reflection, this selection ability increased the probability of not being bothered by multipath. The antennas were quad helix types on vertical cylinders.

 

[biff44]

Re: why not use circular polarization antenna in wireless co

"never be as good as a vertical and a vertical". And what happens when the polarization shifts away from vertical as a signal bounces off a building?

 

[wusen]

Re: why not use circular polarization antenna in wireless co

thanks for your answers...
vfone, you are right, it is hard to implemented circularly polarized in mobiles (especially for dual band and the bandwidth reach 10%). But in BS, it can. why don't use dual circular-polar (one is LHCP and other is RHCP) to achieve diversity (btw ,did anyone even hear about diversity between LHCP and RHCP?can it yield diversity gain with this scheme?). Compare to dual-polar, which polar mistch is 20log10(cos(xita)), Polarization Mismatch between a Linearly and Circularly Polarized Wave is no more than 5dB even AR reach 3.
Several measurement campaign had proved the XPD can even reach 0dB in urban circumstance . So vertical to vertical isnot the best selection.