The planar square-Archimedean spiral located at the center of a dipole has been demonstrated as a valuable passive antenna element in the upper MM-wave and THz regions between about 100 GHz and 2 THz (Bjarnason, E. et al., Appl. Phys. Lett., vol.85, p.3983, 2004). For the coupling of radiation to freespace, there is also a high resistivity silicon hyperhemispherical lens attached to the back of the GaAs substrate. This is a compound-type antenna that is resonant at low frequencies, but broadband at higher frequencies with similar high-frequency performance to the log spiral antenna. The advantage of this structure over previous spiral-based antennas is its dimensional compactness. As in prior works, it is found that most of the radiation couples into the dielectric substrate and that the lens is required to couple the radiation efficiently to free space. A square shaped spiral is used since this shape is easier to make with lithography at the very small micron sizes needed. The dipole length is 540 /spl mu/m, and the dipole arms have a width of 9.2 /spl mu/m.