Lateral surface-wave coupling between branches of a corporate microstrip feeding network often limits the efficiency of millimetre-wave planar arrays. Current feed-network mitigations, such as substrate-integrated waveguides and printed ridge-gap waveguides, require complex multilayer stack-ups or altered line cross-sections. Conversely, radiator-side techniques like electromagnetic band gaps and parasitic stripes leave feed-network losses unaffected. To address this gap, we propose a feature-graded ground stripe that interacts directly with the feed network on a single metallic layer. By using grounded auxiliary stripes and plated metallic vias, this design creates a robust isolation barrier between feeding branches to drain laterally propagating surface-waves before they can recouple. We integrated this approach into an eight-element rectangular dielectric resonator antenna (DRA) array specifically tailored for the 3GPP n257 band. The resulting array delivers a -10 dB bandwidth spanning 25.77 to 28.83 GHz (fractional bandwidth of 11.2%). Furthermore, it achieves a peak realised gain of 18.6 dBi at 28.2 GHz alongside a total efficiency exceeding 90% between 27.0 and 28.5 GHz. Inter-branch isolation (S 23) is maintained below -33 dB across the operational band. Finally, experimental validation of a fabricated prototype shows that the measured reflection coefficient (S 11) confirms the design's practical viability.