Compact Coplanar Waveguide Spiral Antenna With Circular Polarization for Wideband Applications

This letter presents a compact, uniplanar, circularly polarized, coplanar waveguide (CPW) spiral antenna for wideband applications. The antenna is directly fed by a 50-Ω CPW from the outside edge of the spiral, thus a balun for matching is not required. This feed provides the capability to have an entire uniplanar array of spirals. It is found that a thick substrate of high dielectric constant absorbs most of the radiated power and results in a unidirectional radiation pattern, which is desirable in many applications. Therefore, this antenna structure is fabricated on a substrate of high dielectric constant, resulting in miniaturization and capability for integrated system applications. It is experimentally verified that the proposed spiral antenna has stable radiation pattern, and its axial ratio is less than 3 dB over the frequency range of 11.4-17.5 GHz.