Nuclear magnetic resonance (NMR) is one of the most powerful analytical techniques with applications in physics, chemistry, biology and medicine. High signal to noise ratio in NMR spectroscopy and imaging is achieved by hyperpolarization - transfer of polarization from electrons to nuclei. This process requires continuous microwave irradiation. In this project an efficient high power microwave source (f ≈ 100GHz) should be built. It is based on low frequency phase locked loop oscillator followed by a chain of frequency multipliers. The multipliers will make use of varactor diodes.