Bandwidth of the helical beam antenna loaded by a dielectric rod

In this paper, the dielectrically loaded helical antenna is analyzed by means of the surface wave theory and the linear antenna array model. Theoretical and the results obtained by numerical simulations executed by FEKO software show that the deterioration of the axial mode fractional bandwidth of the dielectrically loaded helix relative to the classical Kraus antenna as a consequence of the increased permittivity of the helix core is caused by two effects. The first is due to the fact that the minimum axial mode frequency varies much slower with permittivity of the rod than the maximum frequency does. Second, as the complexity of the propagation increases with the permittivity, the existence of multiple modes on higher frequencies that may carry the electromagnetic energy sufficient to split the beam radiation pattern may cause lowering the maximum beam mode frequency.