Abstract
Wireless devices with no direct access to ports are tested by antenna couplers, which are designed to have wideband performance and an omni-directional radiation field profile for uniform near-field coupling with positional variation. The spiral antenna coupler presented here is designed to be used in a RF-shielded enclosure, requiring a metal backing (λ/83 away at 0.4GHz in this study) to preserve consistent performance, but can also be used separately. The design is a stripline fed spiral antenna with mixed Archimedean and Equiangular antenna equations describing the spiral expansion of the arms. Absorbing material placed around the antenna removes resonances/reflections on the metal backing and reflections from the antenna’s open end. The infinite balun stripline feed is shown to provide high return loss over the required frequency range of 0.4–6GHz. The antenna near- and far-field performance, as well as coupling between identical antennas are measured with and without metal backing to demonstrate the performance as an antenna coupler.
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