**2. Front-end systems and their circuits**

As briefly described in Section 1, a microwave front-end system is directly connected to the radiating element. In most cases, these subsystems provide dual mode operation: receive and transmit mode. In receive mode, the incoming RF signal is very weak and its power needs to be amplified to an adequate level, without adding excessive noise content or distorting the RF signal.

In transmit mode, the outgoing RF signal has to be raised to the highest possible value in order to guarantee an adequate transmission level. In this case too, distortion must be limited in order to preserve the information carried by the RF signal.

Signal routing is often necessary to implement the desired RF path between the digital section and the selected antenna.
