A coupling antenna has a ground plane, a main radiating assembly and a secondary radiating assembly. The main radiating assembly is mounted on the ground plane and has a substrate, a feeding-and-coupling assembly and a shorting member. The feeding-and-coupling assembly has a feeding member, a coupling member and an extension member. The second radiating assembly is mounted on the ground plane, is connected to the main radiating assembly and has a first radiating patch and a second radiating patch. With the extension member and the first and second radiating patches, operating bandwidth of the coupling antenna is improved.