Multiport double layer nearfield geodesic lens antenna in V band

The continuous demand for high data rate communication links is a state-of-the-art in nowadays 5G mobile networks. Millimeter-wave (mmWave) is highly attractive for performing data transmission due to the available bandwidth at such high frequency band. In order to relieve the free space path loss, high gain antennas are required as well as improved coverage characteristics for users within the field of view of interest. As a consequence, reliable 5G point to multipoint communication require stable aggregate gain in the farfield with low roll-off at crossover points between adjacent beams. Previous works based on lenses or quasi optical systems in the mmWave band such as Ruze lenses, Rotman lenses and Luneburg lenses are not suitable to fulfill this requirement. Due to their farfield focusing property, they produce very narrow pencil beams thus resulting in poor performance in terms of beam coverage. A roll-off greater than 3 dB between adjacent beams and an half power beamwidth (HPBW) smaller than 20° is obtained. As a consequence, reliability of communication is reduced over the angular area of interest. In order to guarantee stable aggregate gain characteristics, a novel approach is proposed in this Master Thesis based on defocusing property of a multiport double layer nearfield geodesic lens antenna in the 56-62 GHz frequency band (V band). Here the nearfield property is exploited to widen the beams in farfield, thus increasing dramatically the HPBW and reducing the roll-off between them. As a first analysis , the design and optimization of a single port double layer nearfield geodesic lens has been reported. Furthermore, a five-port double layer nearfield geodesic lens has been designed and simulated as a final case of study. Rigorous analytical formulation aided by CAD tools has been pursued to derive and optimize the geodesic lens profile according to the design requirements. An initial theoretical lens profile has been derived from differential equation resulting in degraded antenna coverage over the angular sector of interest. Indeed, an HPBW smaller than 20° and roll-off equal to 7 dB between adjacent beams has been obtained in the 56-62 GHz band. As a consequence, an optimization on lens profile has been carried out to improve beam coverage capability. The main novelty of the final optimized multiport lens is to achieve an HPBW greater than 20° and a roll-off smaller than 3 dB at crossover points between adjacent beams thus resulting in a stable aggregate gain in 56-62 GHz band. The lens scanning region is equal to ±55° in the H plane thus allowing no degradation in link performance for users in this sectorial area. Multibeam radiation pattern results have been validated in the frequency band of interest. Furthermore, the absolute value and phase of electric field when feeding different ports have been also analyzed thus showing the nearfield focusing property of such lens antenna. As a final consideration, scattering parameters when different ports being fed have been reported for complete analysis.