Parametric study of broadband tunable helix antenna matching

Helical antennas are versatile, but they have almost purely resistive input impedance, so lumped element matching networks inevitably incur power loss. We investigate an alternative matching technique that claims up to 1:1 VSWR with post-fabrication tuning, by using an extension above the ground plane. However, our results show that the lowest return losses may actually occur outside the desired band of operation. We show that the matching technique is dependent on the geometry of the matching structure. In an attempt to bring the best match back inside the operating band, we expand the parameter space of the ground plane extension by considering a double bend which we expect to give more linear impedance transition. We achieved broadband operation with up to 20% fractional bandwidth for -15dB return losses within the targeted 2.4GHz LAN frequency band. Further work is required to derive design equations for this matching geometry.