A base station in a mobile communication network, includes at least one transmission line for transmitting a radio frequency signal. Each transmission line includes a coupling hole. A two-port coupled line includes one or more coupling holes. Each transmission line and the coupled line are couplable to form a coupling by setting the coupling hole of the transmission line against the coupling hole of the two-port coupled line. The coupling enables a signal sample of the radio frequency signal to propagate from the transmission line to the two-port coupled line.