When an satellite earth station transmits a signal to the satellite there are two separate frequencies to worry about. In C-Band the standard transmit frequency is in the range of 5.925 Ghz to 6.425 Ghz. At the same time the earth station antenna is looking for a signal back from the satellite in the range of 3.7 to 4.2 Ghz.
The antenna transmit signal is very strong and the receive signal is weak and so it is possible that the transmit signal will interfere with the receive signal, but to avoid this all antenna feeds are equipped with a transmit/reject filter designed to remove all signals in the transmit range.
Shown in the photograph below are transmit reject filters manufactured by Apollo. Typically sold for $250 on the used market.