Читать книгу Advanced Antenna Array Engineering for 6G and Beyond Wireless Communications - Richard W. Ziolkowski - Страница 25

With 6G data rates promised to be even higher than those of 5G [1–3], a much wider spectrum is needed to accommodate 6G expectations. Unfortunately, a large currently unoccupied spectrum does not exist below 100 GHz. Consequently, it is widely expected that 6G will occupy a significant part of the THz spectrum [2]. Along with terrestrial‐based communication systems, it is anticipated that THz systems will also play a major role in space‐based communications [18, 19].

Currently, the most common definition of the THz band is that it consists of frequencies from 0.3 to 3.0 THz. Recall that the wavelength at 0.3 THz (300 GHz) is just 1.0 mm. Owing to the fact that THz wavelengths are even smaller than the mm‐wave ones, very narrow multiple beams with low probability of intercept (LPI) can be generated from very physically small areas. Beam steering and target tracking again will be indispensable features for THz antennas.

Referring to Figure 1.9, signal attenuation in the lower portion of the THz range is even more severe than in the mm‐wave band. Thus, high‐gain antenna arrays are even more necessary for anticipated 6G operations. Other important related THz technologies that must also be developed to address 6G expectations are high power sources and highly sensitive receivers [20]. Feeding a large array of THz antenna elements of 0.5λ in size using a corporate network is a daunting engineering task. Therefore, it has not been favoured to date. Instead, a more promising approach is to employ an electrically large lens fed by a simple radiating element such as a dipole or a slot or even a small array. To ease the problem of the precise alignment of the antenna and lens, one could integrate the antenna feed with the lens. Antennas with this characteristic are known as integrated lens antennas [20–22].