Antenna systems, devices, and methods for providing both end-fire mm-wave high-frequency signals and low-frequency RF signals from a collocated antenna array in which at least one high-frequency antenna element and a low-frequency antenna element are spaced apart from one another. Grating strips are positioned between the high-frequency antenna elements and the low-frequency antenna element, the grating strips being spaced apart from one another by a defined spacing. The grating strips are configured such that a signal wave from the high-frequency antenna element propagates through the low-frequency antenna element.