Bifocal Polarization Insensitive Fresnel Lens Tuning Using Lubricant Oil for MM-Wave Applications

In this paper, the synergy between use of lubricant oil (Loil) in Fresnel zone lens (FZL) for focal length (FL) tuning for the first time in 27–30GHz band is proposed. This is achieved by filling the cavity of FZL with the Loil according to the required FL of 50 and 142mm. The FL is achieved for both TE ($E_{x}$) and TM ($E_{y}$) polarization, thus providing polarization insensitive tuning. To minimize the impact of the FZL walls on tuning performance, the FZL is additively manufactured with controlled infill percentage and pattern. The Loil and walls of the FZL are characterized for their dielectric constant and loss tangent at 28 GHz using cavity resonator and free-space methods, respectively. In addition, an average increase of 7.4 dBi (5.49 times improvement in the received power) in the realized gain is achieved throughout the band with maximum gain of 22.5 dBi (meas: 20.2 dBi) around 28GHz. Also, the average efficiency of the FZL is 89% throughout the band, thus having very low insertion loss. Because the FZL provides dual polarization, the data throughput is increased by utilizing orthogonal polarization simultaneously for the bifocal case in mm-wave communication. Also, due to the improvement in the realised gain of the transmitting antenna, the proposed solution is also suitable for the wireless power transfer applications. The measurements were conducted to validate the simulation results.