What allows a system to use the same antenna for both transmitting and receiving?

A duplexer is a critical component that enables a system to use the same antenna for both transmitting and receiving signals. It effectively separates the frequencies used for transmission and reception, allowing them to coexist during operation. This separation is essential because the transmitting signal could interfere with the reception of incoming signals if they were on the same frequency.

The duplexer uses different frequency channels to ensure that outgoing and incoming signals do not interfere with one another while making efficient use of a single antenna. In many communication systems, especially in RF and microwave applications, this capability is vital for communication efficiency and helps in maintaining signal clarity.

Other components such as a combiner, switching network, or filter serve different functions and would not provide the same dual functionality as a duplexer. For instance, a combiner is used to merge multiple signals into one, while a switching network is designed to route signals and a filter simply allows certain frequency ranges to pass while blocking others. Thus, while all of these components play important roles in communication systems, only a duplexer fulfills the requirement of using one antenna for both transmitting and receiving effectively.