A switching regulator for controlling transmit antennas of variable impedance, particularly transmit antennas of a keyless access authorization system in or for a vehicle, having an input terminal into which an antenna potential applied or appliable at the transmit antenna may be coupled, and having a control circuit designed to generate a compensation signal as a controlled variable for adapting the antenna potential to an actual output impedance and to establish a slope of the compensation signal depending on the actual antenna potential. The invention relates furthermore to a transceiver circuit with such a switching regulator and to a keyless access control system in or for a vehicle.