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Co Pol and Cross POL

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Ex Member

Jan 23rd, 2010 at 6:03am  
Hi Sir ,

What is the difference between co pol and cross pole feedhorn . Why we have to co pol for some satellites and cross pole feedhorn for some .

Plaease explain me the difference .

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Eric Johnston
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Reply #1 - Jan 23rd, 2010 at 9:57am  
See explanation of co-pol and cross-pol feed assemblies. These examples are two port feeds, with one waveguide for transmit, the other for receive.

Teleport hub antennas are often have four port feeds so they can transmit and receive multiple carriers on both polarisations simultaneously.   To make a 4 port feed, attach a diplexer filter to each port of the OMT.

Satellites operate simultaneously on both polarisations since this reuses the frequency band twice.  Additional frequency reuse is possible using multiple beams, aimed apart from each other.  On a typical satellite there is a transponder interconnection matrix switch so any up beam and polarisation may be cross connected to any downlink beam or polarisation. The way this switch is configured is so as to match the traffic requirement as best as possible.  For example a transponder might be connected west spot vertical to west spot horizontal.  In this case you see your own signals, using cross pol antennas.   Once you have satisfied the traffic demand the problem is that you are left with unused bandwidth in some transponders.  If this turns out to be vertical up and vertical down then maybe sell it off at lower price in view of the inconvenience of co-pol operation for VSAT operation.

Co-pol operation may also be the result of poor satellite design, mismatch of design to actual customer requirements or limitations due to failures of on board components.

Best regards, Eric.
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