An electronic device may include a peripheral conductive housing sidewall with an integral ledge extending towards the device interior. A display cover layer may be supported by the integral ledge. A slot antenna may be formed from a slot in the integral ledge. The integral ledge may be mounted to a surface of a substrate and coupled to a conductive rear housing wall by a conductive layer extending over an additional surface of the substrate. The sidewall may include a vertical portion extending from the ledge to the rear wall. The slot antenna may be fed via near-field coupling using a conductive patch that is located within the slot at the surface of the substrate. The conductive layer, rear housing wall, and vertical portion may form a cavity for the slot antenna. The conductive layer may isolate the slot from interference with a battery, display circuitry, or other components.