Spiral antennas have been adopted a lot over the linear polarization counterparts, since the circular polarizations of their far-field patterns can improve the versatility of wireless communication in multiple-fading and multiple-reflection environment. Nonetheless, there are shortcomings from the conventional spiral antenna systems, which are poor channel selectivity and large physical volumes. Most of the spiral antennas take tapered-shaped metal patterns to have the wide-band, since the basic winding of a uniform line to a circle of a growing radius reduces to a narrow-band. The footprint of the aforementioned antenna should be large for a higher gain. With this, because the balanced feed assures the desirable spiral antenna performance, the differential feed or vertical balun is connected to the input port of the antenna, which makes it accompany a cavity beneath the metal pattern. Especially, when the main radiator is above the bottom PEC of the cavity by the quarter-wavelength, the volume of the cavity-backed and balun-fed spiral antenna becomes improper for portable devices and attachment to a vehicle.