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This paper introduces a novel concept of frequency-independent variable phase-shifters. It is based on the use of circularly polarized (CP) antennas coupled in the near-field. For transmission between two CP antennas in the far-field, a rotation around the boresight axis produces a phase change in the transfer function. This concept is exploited and validated also for near-field coupling between two CP antennas. Therefore, two close-coupled CP antennas can act as a adjustable phase-shifter with the phase-shift controlled by the angle between the structures. The bandwidth depends on the CP bandwidth of the antenna. This concept is valuable for future phase-shifters in mm-wave applications where rotation can be facilitated by MEMS elements.
Sipal, V., Narbudowicz, A. & Ammann, M.J. Using near-field coupled circularly polarized antennas as frequency independent variable phase-shifters, Electronics Letters, vol. 50, no. 11, pp 788-790. DOI:10.1049/el.2014.0874