A tunable wideband omnidirectional circularly polarized antenna regulated by the gravity field

In this article, a tunable wideband omnidirectional circularly polarized (CP) antenna regulated by the gravity field based on the liquid metal Hg is investigated. Under the action of the gravity field, Hg flows in the upper and lower parts by rotating such an antenna, which can constitute dissimilar resonant units to achieve the dynamic regulation of the operating bandwidths. The proposed antenna consists of four tilted glass containers that are filled with Hg in the upper or lower parts, and a feeding structure for power distribution and impedance matching. To verify concept of the design, equivalent prototypes have been fabricated and measured. The measured results are roughly consistent with simulated results within a reasonable error range. The antenna has a 10-dB impedance bandwidth of 44.3% (2.37-3.72 GHz), and a 3-dB axial ratio (AR) bandwidth of 18.9% (2.83-3.42 GHz) when the proposed antenna is not rotated (state I). When such an antenna is rotated (state II), it has a bandwidth of 40.7% (2.35-3.55 GHz) with S11 below −10 dB, and a bandwidth of 22.9% (2.40-3.02 GHz) with AR below 3 dB. Therefore, the operating band of the antenna can be altered between two wide bands. The proposed antenna has the advantages of tunable bandwidth, novel efficient regulation mechanism, and simple structure.