CPW-Fed Three-Arm Archimedean Spiral Antenna for X-band Applications

This paper presents a coplanar waveguide-fed planar 3-arm Archimedean spiral antenna for X-band (8-12) GHz applications. Unlike the traditional two-arm Archimedean spiral antenna (which needs a balun), the proposed three-arm spiral antenna can be fed with coaxial and coplanar waveguide directly without balun and external matching network requirements. This is accomplished by impedance matching of outer arms of the proposed spiral with the coplanar waveguide structure. The geometrical dimensions of the proposed CPW-fed 3-arm spiral antenna are optimized in full-wave 3D electromagnetic simulation tool (CST 2019 studio) to achieve a wide impedance bandwidth, axial ratio bandwidth and positive gain in the X-band. The proposed antenna is designed over a perfect electric conductor (PEC) reflector to achieve a unidirectional radiation pattern. Furthermore, the center arms of spiral are loaded with matched loads to improve the axial ratio (AR) bandwidth. Finally, the performance (impedance bandwidth, AR bandwidth and efficiency) of the proposed antenna is investigated by non-inverting and inverting it to the PEC reflector at a specific distance. Because of its simple feeding structure, positive gain, wide impedance and AR bandwidths, the proposed CPW-fed 3-arm spiral antenna is a good candidate choice for wideband antenna array applications in X-band.