Abstract
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.
Highlights
Wireless technology is evolving towards multi-functional, faster, secure and reliable communication systems occupying compact physical dimensions
A single reconfigurable antenna alone can do the jobs of multiple non-tunable antennas
Electromagnetic interference (EMI) among adjacent antennas can be mitigated through replacing multiple antennas of a system by single reconfigurable antenna
Summary
Wireless technology is evolving towards multi-functional, faster, secure and reliable communication systems occupying compact physical dimensions. Reconfigurability in antennas’ operations are primarily achieved by mechanically tuning antennas’ geometries [2], [5], [7] or integrating electronic components, such as varactor diodes [8], PIN diodes [4], [9], photoconducting switches [6] or RF micro-electromechanical (RF-MEM) switches [10] within the antenna structures. Among electronic reconfigurable antenna technologies, RF MEM switches and PIN diodes have discrete tuning capabilities and varactor diodes have continues tuning properties In this demonstrated research effort, varactor diode is used to design a frequency reconfigurable antenna having continuous frequency tuning from 2.38 to 2.67 GHz. In various applications of modern wireless communications, antennas are required to be conformal in structures, especially in wearable technologies where antennas are mounted on different parts on human body and exposed to frequent physical deformations [11], [12]. The proposed water-based reconfigurable antenna is fabricated by using 3-D printed molds and the fabricated prototype is experimentally tested in different bias states to evaluate its feasibility in frequency reconfigurable operations
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