SatSig topic:

What is port to port Isolation?

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Mar 10^th, 2023 at 3:48am

The port-to-port isolation is defined as the ratio between the power fed into one port of the antenna and received at the other port. Ideally one would like the two ports to be completely independent (infinite isolation) because the signal transmitted from one port will not interfere with the signal transmitted from the other port. The lower the isolation, the more interference there will be between the two transmitted signals.
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Apr 30^th, 2026 at 12:06pm

Here is an example of the use of a C band transmit reject filter used to improve the transmit to receive port isolation.

The white waveguide transmit reject filter at the top (with row of adjustment screws) is connected between the receive output of OMT and the LNB input. Its purpose is to stop transmit energy leaking across into the LNB and overloading the LNB or damaging the LNB.

This is the transmit to receive isolation.

In the image above it would appear that the transmit path (lower black rectangular waveguide into circular waveguide) can be configured for either polarisation. If co-polar operation is chosen then the use of the transmit reject filter is absolutely critical.

Consider that the transmit power might be several watts and the LNB input is extremely low it is very important that the transmit to receive isolation is good. It is easy to overload or burn out and LNB!

Apr 30^th, 2026 at 12:09pm

Here is a similar Ku band arrangement.

Example VSAT feed assembly with transmit and receive ports.
Ku band feed with OMT and transmit reject filter and transmit bandpass filter.

The receive LNB is connected at the top. The transmit BUC is connected at lower left.

The straight through transmit band-pass filter (on the left, 14-14.5 GHz) is designed to stop spurious transmit signals such as 28 GHz getting through to the satellite.

The receive transmit reject filter (shown upwards) stops the 14-14.5 signals getting throuth to the lNB, receiving 12.5 - 12.75 GHz. This filter needs to be low loss and its insertion degrades the noise temperature of the receive system.

Reference: Ku Filter /OMT assembly p/n 718312 Model : 0800-2598 and feed horn Model 0800-1375.

For mounting, the transmit module must be attached at the left and the LNB at the top.