A frequency discriminator is described. The frequency discriminator comprises a power splitter (2) for splitting a signal into a plurality of paths (40, 41, 42, . . . , 4n). At least two of the plurality of paths (41, 42, . . . , 4n) include respective filters (121; 122, . . . , 12n) having different frequency characteristics which are configured to provide respective filtered signals to respective power detectors (161, 162, . . . , 16n. The frequency discriminator comprises an analogue-to-digital conversion section (8) which is configured to receive values of measured powers from the power detectors, to generate digital values of measured powers and to provide the digital values of measured powers to a digital processing section (10). The digital processing section is configured to estimate a value (11) of at least one frequency in the signal in dependence on the digital values, for example the ratio of the digital values, of measured powers and on frequency responses (201, 202, . . . , 20n; FIG. 2) of the filters.