Abstract: Because of the accuracy requirements of tracking radar,the beam width is very narrow.To implement the self-guidance of radar,the technology of multi-band coplanar antenna for tracking radar is described.The design of coplanar antenna, the design of composite feed and the self guiding probability calculation of dual-band radar are discussed specially.Some design examples and simulated results are given.The obtained results show that the application of multi-band coplanar antenna make it possible to use one radar to replace two or more radars.