Here we report on a fabrication and a millimeter-wave performance of reliable and reproducible high-Tc superconducting (HTS) Josephson junctions on MgO substrates using a focused Ga ion beam (FIB). The junction normal resistance Rn can be controlled by making the junction in a series. The Rn depends on space between each junction in the series structure. A mechanism of the junction is proposed by measuring cross-sectional transmission electron microscopy (TEM) images and their X-ray spectra of Ga, Y, Ba, Cu, Mg and O. The junctions with more than 1 µm spaces, and flat and lateral structure are independent each other for the crystallization process. We observe the HTS mixer-antenna performance as fundamental/harmonic mixers in the wide frequency range up to 100 GHz.