Metallic housing of electronic device

A casing of an electronic device, comprising:

• a metallic housing, having an inner surface and an outer surface opposite to the inner surface, and including a back region and at least one side region, the inner surface being substantially a recessed structure, and the metallic housing having a first gap and a second gap each communicating the inner surface and the outer surface, wherein the metallic housing further comprises at least one connecting terminal, and a plurality of apertures are formed on a surface of the at least one gap of the metallic housing;
• a first non-conductive spacer, disposed in the first gap of the metallic housing, and extending from the back region to the at least one side region;
• and
• a second non-conductive spacer, disposed in the second gap of the metallic housing,
• wherein the metallic housing comprises an upper cover, a middle cover and a lower cover, and the first gap is located between the upper cover and the middle cover, and the second gap is located between the middle cover and the lower cover.