Since its inception, the durable, conformal, and low profile equiangular spiral antenna has enticed private enterprise and public entities to expand and enhance applications for biotechnology, communications, military, and space implementation. The spiral antenna's ultra-wideband (UWB), high efficiency, and circular polarized features attract implementation where physical and electromagnetic environment conditions fluctuate such as intelligence gathering, astronaut extra vehicular activities, satellite communications, navigation, and disaster communications. Impedance matching the spiral is critical. Common solutions utilize a balun or an impedance transformer. These solutions preserve the antenna's efficiency and radiation profile. Some examples of balun and impedance transformers applied to spiral antennas include integrating planar microstrip baluns with vias, complex coplanar strip designs, multi-layer substrates with strip lines, coaxial cables, perpendicular feed lines, etc. Balun designs have a limited impedance bandwidth or add manufacturing complexity impeding spiral antenna implementations. NASA has developed a conformal S-band equiangular spiral antenna constructed from commercially available e-textiles made from polyester cloth plated by a mixture of silver, copper, and nickel. The e-textile fabrication made the antenna malleable to clothing, spacesuits, flags, etc.; however, the inflexible coaxial cable balun leaves the structure vulnerable to damage. Unforgiving environments, such as outer space, necessitate design and fabrication considerations for resiliency and robustness.
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