A Numerical Study of Coaxial Helical Antennas

A FEKO model was constructed to investigate two helical antennas integrated coaxially on a shaped ground plane. One antenna was designed to have a reasonable gain and axial ratio (AR) from 0.5 – 0.9 GHz and the other from 1.0 – 1.6 GHz. In principle, the antennas could be connected in parallel to provide a near 50 ? input impedance and act as a wideband antenna. However, this connection is problematic and can make fabrication more complex while changing the input impedance in unpredictable ways. An alternative is to use a microstrip impedance transformer to provide a 50 ? input to each antenna. Then a broadband splitter can be used for a single feed wideband antenna. Otherwise, these two ports with switched input allow dual-band operation. The FEKO model is described and simulation results are presented for both cases. These results encourage further virtual prototyping and prototype fabrication for model validation.