Design of “masthead” combiners

In most communications systems, the transceiver output is connected to the antenna by means of a selective diplexer, allowing TX and RX to share a single antenna. Very often, however, the antenna is located on the top of a tower, and a transmission line of not negligible length is required for the transceiver connection. Even if high an quality transmission line is used, the additional losses introduced worsen the overall noise figure of the receiving system. Recently a combiner to be mounted at the antenna output (on top of the tower) has been proposed which allows to compensate the noise figure degradation due to the cable losses. In this paper we discuss the design of this device (here called “masthead” combiner) which allows to connect a low noise amplifier just at the output of the antenna, while enabling the transmitted power from the TX to arrive to the antenna. After describing the design approach (based on polynomial modeling), some examples of the attainable results are reported.