A sub-terahertz (THz) band microstrip antenna is proposed in this paper, which has an unslotted, easy to fabricate design. The presented antenna has a wide impedance bandwidth of 0.114 THz (from 0.093 THz to 0.207 THz), where S11 < - 10dB. It also has a wide fractional bandwidth percentage of 76%. Once the computer simulations are performed, it is observed that the antenna has a maximum radiation efficiency of 98% throughout the operating frequency range. Moreover, it has an omni-directional radiation character and has a compact size of 1000 x 1000 x 100 mu m3 (0.31 lambda x 0.31 lambda x 0.031 lambda, where lambda is the wavelength at the lowest operating frequency). Finally, the 2 x 2 multi-input multi-output (MIMO) version is analyzed and the isolation between the elements is determined as less than - 17 dB across the band of operation. With all the abovementioned features, the proposed antenna outperforms from most of other state-of-arts and indicates that it is a suitable candidate for short range sub-THz applications.