Reconfigurable Axial-Mode Helix Antennas Using Shape Memory Alloys

Reconfigurable structures based on smart materials offer a potential solution to realize adaptive antennas for emerging communication devices. In this paper, a reconfigurable axial mode helix antenna is studied. A shape memory alloy spring actuator is used to adjust the height of a helix antenna. With the total length of the helix wire fixed, the pitch spacing and pitch angle are varied as the height is varied. This in turn can alter the antenna pattern in order to adjust to altered operating conditions. In order to undertake the design, the Kraus equations for the axial mode helix are compared with simulation results, and their range of applicability is clarified. It is shown that based on these equations, antenna gain variation is possible by varying the height of the antenna, while keeping its conductor length fixed. We then show that a pattern can be reconfigured using a two-helix structure. Finally, a proof-of-concept helix antenna is implemented using a shape memory alloy actuator. Measurement results confirm that the pattern can reconfigure while maintaining a reasonable impedance match.