In the paper, mixers are described that consist ofMresistive diodes, e.g. Schottky-barrier diodes in a parallel connection. When such mixers are used in frequency convertors, the diodes are pumped by signals having a frequencyMtimes lower than the frequency of conventional local oscillators. A phase shift equal to multiples of 2π/Mis necessary between the pump signals. The frequency multiplication, which is usually carried out in the local-oscillator circuit, is done in the mixer. For this reason it is possible to use pump sources that are much simpler than conventional local oscillators. Often the harmonic mixers proposed in the paper are more complicated than the mixers used so far. Sometimes, however, circuits of moderate complexity can be found, so that a simplification of the frequency convertors is possible. This will be shown by mixers that are pumped at the first or second subharmonic, respectively. Theoretical investigations show that the conversion losses of harmonic mixers are slightly higher than those of conventional mixers.