Polarization　has　always　been　an　important　issue　in　modern　communication　systems,　especially　in　sensitive　measurements.　Conventional　polarization　converters　show　limited　applications　due　to　their　large　size　and　narrow　bandwidth.　In　this　paper,　we　demonstrate　an　ultra-wide　band,　multifunctional,　and　highly　efficient　metamaterial-based　polarization　converter　that　is　capable　of　converting　a　linearly　polarized　wave　into　its　cross-polarized　wave　and　circularly　polarized　wave　over　different　frequency　bands.　The　design　principle　is　based　on　the　field　transformation　theory　and　the　anisotropic　plate　is　made　with　high/low　permittivity　strip　metamaterials.　The　simulation　results　show　that　the　metamaterial-based　polarization　converter　is　able　to　achieve　linear-to-linear　conversion　over　11.5-12.6　GHz,　and　linear-to-circular　conversion　over　two　frequency　bands,　3.0-11.5　GHz　and　12.6-17.0　GHz,　with　an　average　polarization　conversion　efficiency　over　90%.　The　polarization　converter　proposed　in　this　paper　provides　an　important　stepping　stone　for　future　communication　systems＇　polarization　control　and　can　also　be　extended　to　higher　frequency　bands.