A circularly polarized patch antenna assembly, comprising: - a substrate having a substrate penetrating hole penetrating the substrate, the substrate having a bottom face, a top face opposite to the bottom face, and four side faces connected between the bottom face and the top face; - a radiation metal piece attached on the top surface of the substrate and provided with a through hole corresponding to the substrate penetrating hole; - a grounded metal piece attached on the bottom surface of the substrate and having a sheet, wherein the sheet has a sheet penetrating hole corresponding to the through hole, wherein the sheet penetrating hole has an inner diameter larger than that of the substrate penetrating hole, - a signal-inputting body penetrating the substrate penetrating hole, the through hole and sheet penetrating hole, the signal-inputting body is electrically connected with the radiation metal piece to form a signal-inputting point, - a plurality metal pieces for down converting the resonant frequency of the antenna, the plurality of metal pieces extend from four sides of the sheet, wherein metal pieces are adhered on the side faces of the substrate, characterized in that the metal piece on any one side face is arranged diagonally with respect to the opposite metal piece on the opposite side face, such that a projection of said opposite metal piece on said one side face is symmetrical to said one metal piece with respect to the centre vertical line of said side face. - the metal pieces further extend to the top face of the substrate, wherein the area of the portion of the metal piece on the side face of the substrate is smaller than half area of the corresponding side face, - the signal-inputting body has a body and a head portion at one end of the body, wherein the head portion has a diameter larger than that of the through hole and is in contact with the radiation metal piece, wherein the body penetrates the through hole, the substrate penetrating hole and the sheet penetrating hole and exposes out of the sheet penetrating hole when the signal-inputting body is placed on the radiation metal piece, whereby a signal can be transmitted from the radiation metal piece to the exposed end of the body. - a substrate having a substrate penetrating hole penetrating the substrate, the substrate having a bottom face, a top face opposite to the bottom face, and four side faces connected between the bottom face and the top face; - a radiation metal piece attached on the top surface of the substrate and provided with a through hole corresponding to the substrate penetrating hole; - a grounded metal piece attached on the bottom surface of the substrate and having a sheet, wherein the sheet has a sheet penetrating hole corresponding to the through hole, wherein the sheet penetrating hole has an inner diameter larger than that of the substrate penetrating hole, - a signal-inputting body penetrating the substrate penetrating hole, the through hole and sheet penetrating hole, the signal-inputting body is electrically connected with the radiation metal piece to form a signal-inputting point, - a plurality metal pieces for down converting the resonant frequency of the antenna, the plurality of metal pieces extend from four sides of the sheet, wherein metal pieces are adhered on the side faces of the substrate, - the metal pieces further extend to the top face of the substrate, wherein the area of the portion of the metal piece on the side face of the substrate is smaller than half area of the corresponding side face, - the signal-inputting body has a body and a head portion at one end of the body, wherein the head portion has a diameter larger than that of the through hole and is in contact with the radiation metal piece, wherein the body penetrates the through hole, the substrate penetrating hole and the sheet penetrating hole and exposes out of the sheet penetrating hole when the signal-inputting body is placed on the radiation metal piece, whereby a signal can be transmitted from the radiation metal piece to the exposed end of the body.