Spiral, helical, and rod antennas

Abstract

Various antennas radiating a circularly polarized wave are reviewed on the basis of numerical techniques. The method of moments, the finite-difference timedomain method, the beam-propagation method, and the finite element method are employed to clarify the operation principles of spiral, helical, and rod antennas. A novel type of spiral antenna (a metamaterial-based spiral antenna) can provide a dual-band counter-circularly polarized wave. Since the operation principle of an endfire-mode helical antenna is very close to that of a dielectric rod antenna, the so-called discontinuity-radiation concept of a surface-wave antenna is discussed using a dielectric rod. Modification of the dielectric rod is studied to achieve a higher gain. A rod antenna based on an artificial dielectric is also investigated using a periodic structure of circular metal disks.