Multi-band antenna

A multi-band antenna, comprising:

• a ground plane;
• a radiation element comprising a first portion and a second portion electrically connected with each other, wherein the first portion is adjacent to an edge of the ground plane and has a feeding point;
• a first extension element extended from the edge of the ground plane and spaced from the first portion by a first coupling distance;
• and
• a second extension element extended from the edge of the ground plane and spaced from the second portion by a second coupling distance,
• wherein the multi-band antenna is operated in a first band through the radiation element, and a feeding signal from the radiation element excites the first and the second extension elements through the first and the second coupling distances so that the multi-band antenna is operated further in a second band and a third band,
• wherein the radiation element, the first extension element and the second extension element are arranged in sequence along the edge of the ground plane.