We report on the performance of dielectric rod waveguide-coupled CMOS-based sources and detectors. The 252 GHz resonant field-effect-transistors-based THz detector is coupled to a Si rod. A similar rod is attached to a voltage control oscillator based on a Colpitts oscillator topology with optimized third-harmonic emission frequency at the same 252 GHz. A dielectric rod, implemented in this work, is employed as an antenna for coupling into a free space, as a transition element from the source or detector to the standard metal waveguide, or to enable the rod-to-rod coupling of a source-detector system. A dielectric rod-coupled system enables it to reach >60 dB signal-to-noise ratio for an equivalent noise bandwidth of one Hz. The knife-edge scans revealed the minimum half-width at half maximum of 0.24 mm at 252 GHz enabling high-resolution imaging applications. The obtained results demonstrate the high-efficiency coupling CMOS elements and Si rods. This concept can be applied to both sensing and THz imaging.