Development of an electron cyclotron heating (ECH) mirror antenna and MW gyrotrons for power modulation experiments in GAMMA 10 has been started in order to generate and control the high heat flux and to make the edge-localized mode (ELM)-like intermittent heat load pattern for divertor simulation studies. A peak heat flux of more than 10 MW/m2 on the GAMMA 10 axis has been obtained during ECH injection within the available power of ECH. This value almost corresponds to the steady-state heat load of the divertor plate of ITER. However, we need a substantial upgrade of the heating power to approach the ITER level ELM energy density. We carry out a design study for a mirror antenna and higher power gyrotrons in order to generate higher intermittent heat flux in GAMMA 10 tandem mirror for future divertor simulation studies.