This paper presents the micromachining based fabrication process of a 140 GHz planar antenna array based on gap waveguide technology to be used in next generation backhauling links. Each antenna element in the bigger 3D-array to be used in LOS MIMO configuration designed to have about 30dBi gain. Each antenna element in the big array consists of several metal layers such as the cavity backed radiation layer and a corporate feed network layer. In this work, we focus on the single antenna array element. Considering some fabrication difficulties as well as focusing on batch fabrication, three different micromachine techniques, SU8 fabrication, PDMS molding and injection molding of polymer OSTEMER has been utilized to fabricate the single antenna device.