Signal combining apparatus comprising: an input port for receiving an input signal from a signal generator; an output port for outputting a signal to a signal analyser; a plurality of test ports for connecting the apparatus to a plurality of devices under test (DUTs), the apparatus further comprising: a splitter for dividing the signal received at the input port into a plurality of signals; a plurality of transmit signal paths, wherein each of the plurality of transmit signal paths is configured to transmit one of the plurality of signals output by the splitter to an input of one of a plurality of duplex combiners; and a plurality of receive paths, wherein each of the plurality of duplex combiners is configured to: receive one of the plurality of signals from one of the plurality of transmit paths; transmit the one of the plurality of signals from the one of the plurality of transmit paths to one of the plurality of test ports; receive a signal from one of the plurality of test ports; and transmit the signal received from the one of the plurality of test ports to one of the plurality of receive paths, characterised in that the apparatus further comprises: a signal relay, the signal relay being configured to receive one or more signals through one or more of the plurality of receive paths and to output a single composite signal to the output port, the single composite signal output to the output port containing the signals received from the one or more of the plurality of receive paths. an input port for receiving an input signal from a signal generator; an output port for outputting a signal to a signal analyser; a plurality of test ports for connecting the apparatus to a plurality of devices under test (DUTs), the apparatus further comprising: a splitter for dividing the signal received at the input port into a plurality of signals; a plurality of transmit signal paths, wherein each of the plurality of transmit signal paths is configured to transmit one of the plurality of signals output by the splitter to an input of one of a plurality of duplex combiners; and a plurality of receive paths, wherein each of the plurality of duplex combiners is configured to: receive one of the plurality of signals from one of the plurality of transmit paths; transmit the one of the plurality of signals from the one of the plurality of transmit paths to one of the plurality of test ports; receive a signal from one of the plurality of test ports; and transmit the signal received from the one of the plurality of test ports to one of the plurality of receive paths, characterised in that the apparatus further comprises: a signal relay, the signal relay being configured to receive one or more signals through one or more of the plurality of receive paths and to output a single composite signal to the output port, the single composite signal output to the output port containing the signals received from the one or more of the plurality of receive paths. a splitter for dividing the signal received at the input port into a plurality of signals; a plurality of transmit signal paths, wherein each of the plurality of transmit signal paths is configured to transmit one of the plurality of signals output by the splitter to an input of one of a plurality of duplex combiners; and a plurality of receive paths, wherein each of the plurality of duplex combiners is configured to: receive one of the plurality of signals from one of the plurality of transmit paths; transmit the one of the plurality of signals from the one of the plurality of transmit paths to one of the plurality of test ports; receive a signal from one of the plurality of test ports; and transmit the signal received from the one of the plurality of test ports to one of the plurality of receive paths, characterised in that the apparatus further comprises: a signal relay, the signal relay being configured to receive one or more signals through one or more of the plurality of receive paths and to output a single composite signal to the output port, the single composite signal output to the output port containing the signals received from the one or more of the plurality of receive paths. receive one of the plurality of signals from one of the plurality of transmit paths; transmit the one of the plurality of signals from the one of the plurality of transmit paths to one of the plurality of test ports; receive a signal from one of the plurality of test ports; and transmit the signal received from the one of the plurality of test ports to one of the plurality of receive paths, characterised in that the apparatus further comprises: a signal relay, the signal relay being configured to receive one or more signals through one or more of the plurality of receive paths and to output a single composite signal to the output port, the single composite signal output to the output port containing the signals received from the one or more of the plurality of receive paths. a signal relay, the signal relay being configured to receive one or more signals through one or more of the plurality of receive paths and to output a single composite signal to the output port, the single composite signal output to the output port containing the signals received from the one or more of the plurality of receive paths.