The invention relates to a high-gain planar wide-frequency antenna which relates to a microwave technology and comprises an Archimedean spiral antenna radiation sheet, a tapered balun and a shell, wherein a reflection cavity is arranged in the shell, and the Archimedean spiral antenna radiation sheet is connected with a signal source accessing end through the tapered balun. The invention has the advantages that the gain of a wide-frequency spiral antenna is improved to a great degree, the circular polarization characteristic of far-field radiation is good, and meanwhile, the standing wave of the whole antenna system also has better performance. The invention has high gain, stable gain, lower axial ratio and wide application potential in the aspects of military affairs and civil use.