the best antenna design is shown in Fig. 10.14. We may observe that the best design antenna exhibits an ultra-wide band behavior starting from 250 to 325 GHz. Thus, it covers the whole low THz frequency band defined by the [1]. The antenna resonates at 300 GHz with a very low S11 value below - -70 dB. Additionally, we notice that the full ground case presents a worse behavior with S11 below - -10 dB in very limited bandwidth and levels that do not become less than - 10 dB. The axial ratio frequency response plot is presented in Fig. 10.15. We notice that the full ground case obtains axial ratio values quite higher than 3 dB and thus does not present circular polarization. Moreover, the partial ground case exhibits circular polarization from about 294-311 GHz. Therefore, the circular polarization bandwidth is about 17 GHz. Overall, SSA was able to obtain a solution to the antenna design problems that fully covers the strict design requirements for both 6G operation and circular polarization. 10 THz Antenna Design Using SSA for 6G Curve Info dB10normalize(GainTotal) Setup 800GHz LastAdaptive Freq= 300GHz' Theta= 90deg -2.40 -4.80 -7.20 -9.60 Fig. 10.10 Partial ground case: Radiation pattern of the best obtained design by SSA at 300 GHz. O = 90° 10.6 Conclusion In this book chapter, we presented a wide band antenna design framework for low THz band for future 6G wireless communications. The optimization algorithm used was SSA, which proved to be very effective in antenna design. The obtained antenna presents an ultra-wide band behavior that covers the whole band from 250 to 325 GHz. The S11 - AR bandwidth in this case is about 17 GHz. Moreover, the design is at a frequency of 300 GHz, the antenna gain is 3.48 dBi, and the radiation efficiency is about 98%, which can be considered satisfactory. S.K. Goudos and M. A. Matin Curve Info dB10normalize(GainTotal) Setup300GHz : LastAdaptive Freq= 300GHz Phi='Odeg -5.00 -10.00 -15.00 -20.00 Fig. 10.11 Full ground case: Radiation pattern of the best obtained design by SSA at 