Pattern Reconfigurable Antennas at Millimeter-Wave Frequencies: A Comprehensive Survey

Millimeter-wave bands (around 28, 38, 60, and 73 GHz) are anticipated to play a decisive role in the hosting of future wireless systems. The necessity of smart antennas to adaptively meet the requirements of the wireless links calls for new pattern reconfiguration antennas with beam-steering and/or beam-shaping capabilities. This paper reviews the latest research contributions on pattern reconfigurable antennas at mm-Wave frequencies, proposing an original classification according to the reconfiguration technique and technology. The analyzed systems are divided into two main groups: Reconfigurable and non-reconfigurable feeding antennas. Phased-arrays antennas are the main component of the first category, whereas other reconfigurable means such as the use of metasurfaces or advance materials like liquid crystal or graphene form the second group, devoted to non-reconfigurable feeding antennas. Furthermore, some insights and theoretical background are provided to help the reader understand and appreciate the uniqueness of every solution. Similarly, the beam-scanning and beam-shaping performance of some of the discussed works is analyzed. Finally, some instructive remarks and open research challenges are discussed, with the aim of providing some guidelines for potential new works on the field.