A planar oscillator is provided includes an oscillator portion formed by four oscillator arms, the four oscillator arms defining two orthogonal half-wave oscillators, each oscillator arm being of a square and these oscillator arms being arranged in a square configuration, each oscillator arm having a feeding terminal defined at a corner thereof facing another oscillator arm; a connective portion connected among these oscillator arms so that these arms are connected with each other; and a medium base plate for printing the oscillator portion and connective portion thereon. In addition, a plurality of through holes is defined in the medium base plate. The antenna made according to the invention is simple and compact in construction and good in performance. In addition, the antenna is easy to be manufactured and assembled. Moreover, the antenna of the invention benefits from wide bandwidth, high gain and cross polarization ratio, and excellent isolation.