...
The feed is the part of the front end that converts electromatic electromagnetic waves propagating in free space into electrical signals in a wire. Technically it is part of the antenna and not the receiver.
...
Some antenna feeds are single ended so that only one low noise amplifier (LNA) is required per polarization. Other feeds have multiple outputs per polarization and these those outputs need to be combined. To avoid losses in the combining circuits, one LNA is required per output.
Recently, broadband circular polarized feeds are being developed based on a conical topology. Even with circularly polarized feeds, all polarization products will be correlated to help calibrate delay biases related to polarization impurity.