In this paper, we present a comprehensive study on the operation of an antenna-coupled THz bolometer based on a micro-machined SOI-CMOS thermal sensor. The pixels are designed to operate at room temperature in vacuum. We focus on a new planar skirt antenna, which combines high sensitivity within a 0.6-1.2 THz band and 30° HPBW. We present an overview of the design considerations, as well as the characterization results which were obtained with both broadband and CW THz sources. The NEP of the pixel is of the order of 25 pW/Hz1/2, with responsivity 100 mA/W at the optimal operating point. The peak responsivity to a broadband THz signal is 600 mA/W. The ease of integration with a read-out circuit and the low power dissipation make this type of pixel a good candidate for focal plane array architecture.