A transmitter comprising a planar antenna including a ground plane and first and second spiral radiating elements wrapping around the ground plane, and a driving circuit. Proximal ends of the spiral radiating elements terminate near points located along a perimeter of the ground plane. Exactly one of the first and second spiral radiating elements are electrically isolated from the ground plane. The first and second spiral radiating elements are wound in the same direction for approximately a single turn and increase in thickness for approximately three-fourths of the turn. The driving circuit drives one of the first and second spiral radiating elements.