Terahertz technology has grown much interest especially in the imaging field. This development, compliant with the low-cost sub-micron CMOS process for focal plan array configuration, addresses some issues about the performances of antennas on a silicon substrate and on a reduced metal stack. Here, two antenna geometries are studied on different electromagnetic (EM) environments and coupling characteristics with the rectifying MOSFET detector. By using electromagnetic band gap (EBG) surface with co-design between the MOSFET and the antennas, S11 of -18.2 dB with 5.8-dBi gain and a radiated front-to-back ratio of 10.1 dB are achieved around 290 GHz.