Weather radar for measuring radar signals in the GHz range with a receiver containing at least one signal path, the receiver comprising a receiving facility for an incoming radar signal, on which a test signal generated by a test signal generator is superimposed in a coupler, and a processing device to amplify, filter and convert both signals to lower frequencies, wherein for filtering a matched filter is provided, and with an evaluation device in which calibration parameters of the signal path are derived from the test signal for the frequency of the test signal in order to determine the signal strength of the received radar signal, wherein the test signal is superimposed with at least one frequency differing from the frequency of the radar signal, so that the radar signal and the test signal are processed separately from one another by the evaluation device, and the calibration parameters of the signal path for the frequency of the radar signal are determinable from the test signal through a modeling of the frequency dependence of the calibration parameters for frequencies around those of the radar signal.