The signal loss caused by full antenna polarisation mismatch

[leszcz]

Antenna polarisation

Hi,
im designing a device using zigbee protocol for communication (CC2420 chip). For this chip i have chosen a 2,4GHz monopole (www.antenova.com). The antenna is lineary polarised. The thing is that this device can sometimes transmit in vertical and sometimes in orthogonal position. The reciver (equiped with the same antenna) will stay in the same position.

How strong will be the signal loss in the case of total polarisation mismatch ? How can I avoid this problem ? Will the circular polarised antenna solve it ? If yes then where can I find such antenna for this puprose ?

Thank u in advance for response.

 

[plasma]

Re: Antenna polarisation

try this site

**broken link removed**

pl

 

[kato01]

Re: Antenna polarisation

for linear pol, misspolarization goes with 20log(cos(alfa)) where alfa is the angle betwwen the polarization vectors.
Mind you, we are talking about sum vector of the Hpol and Vpol

With CP, the axial ratio would be the loss factor, however the sensitivity will be lower to pol missmatch

 

[leszcz]

Re: Antenna polarisation

Yeah i know the 20log(cos(alfa)) formula but it means that for alfa=90 i shall not be able to recive any signal at all. And I think its not the whole truth. As far as i know mobile phone is linear polarised as well and its still working in various positions ...
The other problem is that all antennas for zigbee applications are linear polarised so sth is still not clear for me.

@ Plasma : what shall I be looking for on this page , there are loads of information ...

Thank u

 

[jallem]

Antenna polarisation

Unless you are planning to use both the receiver and
transmitter in absolute line of sight ( no obtructions)
you do not need to worry about polarization. In non LOS
even though the antenna could be vertical polarization
what gets to the other end is a combination of
both, horizontal and vertical due to multiple reflections.

 

[leszcz]

Re: Antenna polarisation

the antenna will be placed on the back of a man, and the reciver can be placed somwhere nearby. The problem is what happens with the transmission when someone will be sleeping , the polarisation will not match then (around 90 degrees) and there will be no direct line-of-sight connection. I think I will have to rise the transmission power in this case and hope it will still be operating.

Thank u for ur answer anyway