| dc.description.abstract | Fifth-generation (5G) wireless communication networks have been rapidly expanding in recent years. However, due to the higher frequency bands used in 5G applications compared with previous generations, it is more difficult for electromagnetic waves to transmit through the air or pass through buildings. To avoid the costs of increasing assembled antenna density, one possible solution is beam-steering antennas. Reflectarrays and metasurfaces play an important role in beam-steering applications.
Reflectarrays and metasurfaces basically use the same concepts that originated from other types of directive antennas, such as parabolic reflectors, except that the structure size and periodicity of reflectarrays are around half a wavelength, whereas those of metasurfaces are usually sub-wavelength. Reflectarrays and metasurfaces are normally installed on a flat surface that consists of a large amount of well-organized meta units and an illuminating feed antenna. Their working principle is phase discontinuity across the surface. Numerous applications, including wavefront shaping, beam steering, frequency selecting, power amplifying, power combining, etc., are based on this principle.
The construction of dynamically tunable reflectarrays or metasurfaces is relatively easy and can be accomplished by changing the external conditions or adjusting one or more of the unit cell characteristics. All unit cells can be managed the same way to manipulate plane wave reflections and transmission coefficients. The unit cells can also be tuned separately for wavefront shaping, beam steering, etc. In general, intrinsic losses associated with control components, as well as their tunability range, limit the effectiveness of tunable reflectarrays and metasurfaces.
The objective of the present research is to investigate the performance of several possible tunable reflectarrays and metasurfaces used for beam steering. The use of different types of controlling methodology, including mechanical and electrical tuning, is examined in depth. The simulation results demonstrate the possibility of a tunable reflection with a phase shift range over 180 degrees. As well, an electrically tunable reflectarray is realized using varactor diodes. | en |
