Improved feed line networks for antenna arrays operating at millimeter wave frequencies are provided for constructing planar antenna arrays printed on the surface of a dielectric substrate. A planar antenna array includes an array of planar radiator elements interconnected through a feed line network of planar coplanar transmission lines that enable high-efficiency operation, at millimeter wave operating frequencies. For example, a feed network may be formed with a network of coplanar strip line transmission lines including one or more coplanar strip line (CPS) and one or more coplanar waveguide (CPW) transmission line, which are interconnected using balun structures, to enable high efficiency operation at millimeter wave frequencies.