Modern wireless networks such as 5G require multiband MIMO-supported Base Station Antennas. As a result, antennas have multiple ports to support a range of frequency bands leading to multiple arrays within one compact antenna enclosure. The close proximity of the arrays results in significant scattering degrading pattern performance of each band while coupling between arrays leads to degradation in return loss and port-to-port isolations. Different design techniques are adopted in the literature to overcome such challenges. This paper provides a classification of challenges in BSA design and a cohesive list of design techniques adopted in the literature to overcome such challenges.
In this paper, a frequency reconfigurable, conformal, durable, optically transparent, and unidirectional antenna design is demonstrated for the first time. In the demonstrated design, continuous frequency tuning is achieved by integrating a varactor diode in a folded dipole radiator, which is backed by a water-filled reflector to produce unidirectional radiation pattern mimicking the radiation characteristics of microstrip patch antennas. The radiating component of the explored antenna is manufactured from transparent conductive fabric, which has about 72% optical transparency and occupies a small fraction of the entire antenna. The water-filled reflector is located underneath the dipole radiator. Water is contained inside a rectangular box made from flexible-transparent-hydrophobic polymer, polydimethylsiloxane (PDMS). Both water and PDMS are highly transparent, moreover, PDMS has excellent flexibility and water is a liquid, thus, the demonstrated antenna exhibits excellent transparency and durability against physical deformation. The tiny varactor diode integrated in the folded dipole radiator has insignificant effect on the overall transparency and flexibility of the antenna. The explored design has been numerically investigated and experimentally validated through measurements. Measurements show continuous frequency tuning from 2.38 GHz to 2.67 GHz with an average 10-dB return loss bandwidth of about 170 MHz. Moreover, the antenna maintains good front-to-back ratio in the entire operating band.INDEX TERMS 3-D printing, composite, conformal, folded dipole, polymer, pure water, tunable.
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