1. Introduction
As wireless communications evolve rapidly, the fifth generation (5G) communication technology is becoming of great importance due to its high-speed data transfer rates, low latency and high volume of traffic density [1]. According to the spectrum division, the 5G bands contain two parts: the Sub-6G band (450–6000 MHz) and the millimeter-wave band (24.25–52.6 GHz [2]. Due to the depletion of spectrum resources in the Sub-6G band, there is a growing focus on using the millimeter wave (mm-wave) band.
Several mm-wave antennas have been developed [3,4]. The antenna efficiency is degraded by the increasing ohmic losses and surface wave at mm-wave. DRAs have been investigated since the 1980′s and are made of dielectric ceramic material with the advantages of no ohmic losses and extremely low dielectric losses, especially at high-frequency (mm-wave) [5]. Therefore, DRAs…
