A microwave heating device includes a variable frequency microwave power supply, a waveguide launcher, and a fixture to contain a material to be heated, with the fixture located directly adjacent to the end of the launcher. All heating occurs in the near-field region, i.e., no cavity modes or standing waves are established within the fixture. This condition may be insured by keeping the thickness of the fixture or workpiece under one wavelength (at all microwave frequencies being used). The launcher is preferably a horn configured to spread the microwave power laterally over a selected area while maintaining a single propagating mode. The invention may be used to enhance catalytic reactions for research and other purposes. Alternatively, the invention may be configured to perform spot curing or repair operations involving adhesives and composites.