# Computational Analysis of a 200 GHz Phased Array Using Lens-Coupled Annular-Slot Antennas
## 1 Introduction  
With the investigation and development of fifth-generation mobile communication technology (5G) in recent years, a variety of advanced applications such as virtual reality (VR), augmented reality (AR), and internet-of-things (IoT) have been proposed and gradually commercialized [1]. Therefore, research activities have been initiated for beyond 5G or even sixth-generation communication technology (6G) for wireless data links with much higher performance, such as larger capacities, higher data rates, and lower latency [2]. Although there is no unified or clear definition for beyond 5G or 6G yet, data rates in the range of 100 Gbps are expected in the near future. Such high data rates require a higher carrier frequency (e.g., in the mmW-THz region (30 GHz to 10 THz)) and a larger antenna gain [3, 4].  
Due to the narrower beamwidths in the mmW-THz frequency range (compared with microwave frequencies), point-to-point communication with dynamic beam steering and forming is required. As a result, phased array technology has become an attractive solution to realize higher directivity, better signal-to-noise ratio, and beam steering and forming for tracking users and navigating blockage [5, 6, 7]. However, data links in the higher frequency regions such as the THz bands (0.1-10 THz) typically have a limited link budget and degraded spatial coverage due to the significant path loss and limited available power (so-called THz gap) [8], which becomes a major issue for realizing advanced THz phased array systems with sufficient power, wider bandwidth, and beam-steering capability. To cope with significant path loss in the THz bands, lens-coupled antennas that have been widely employed in THz detection, imaging, and radiating [9, 10, 11] can provide higher gain and reduce surface wave losses (substrate mode loss).  
In this paper, we proposed a novel approach for realizing a high gain THz phased array using the lens-coupled antenna configuration. For a prototype demonstration and feasibility study, A 200 GHz lens-coupled phased array using annular-slot antennas is designed, simulated, and analyzed. In the lens-coupled phased array design, multiple ASAs were coupled to an extended hemispherical silicon lens, and the element distance (_d_) was 0.55\(\lambda\) (\(\lambda\) is the wavelength in the silicon dielectric) as shown in Figure 1 (a 1 \(\times\) 5 array is depicted as an illustrative purpose). A 1 \(\times\) 3 array and 1 \(\times\) 5 array were implemented with the extended hemispherical silicon lenses using different extension lengths (_L_). The full-wave simulation was performed for the above configurations. The simulation results show that a \(\pm\)22\({}^{\circ}\) scanning angle (\(\theta\)) and a \(-\)10 dB sidelobe level can be achieved by using a 1 \(\times\) 3 array and an extended hemispherical silicon lens (radius (_R_) of 5000 \(\upmu\)m and \(L\) of 1000 \(\upmu\)m). Compared with a conventional 1 \(\times\) 3 array on a silicon dielectric half-space without the silicon lens, the lens-coupled 1 \(\times\) 3 array achieves more than a 10 dB gain improvement. In addition, by applying a 1 \(\times\) 5 array with a smaller extension length (_L_ of 250 \(\upmu\)m) lens, a larger scanning angle of \(\pm\)33\({}^{\circ}\) can be realized. To the best of our knowledge, it is the first time that a lens-coupled phased array has been systematically designed, investigated, and analyzed. The proposed approach for designing phased array antennas can be adopted in THz wireless communication devices such as THz transmitters or receivers. The paper is described as follows: Section 2 presents the configuration and theory of the proposed lens-coupled ASA array. The simulation results of a 1 \(\times\) 3 array and a 1 \(\times\) 5 array for different extension lengths are discussed in Section 3. Section 4 concludes this article.