This paper presents two SiGe power detector circuit designs intended for W-band passive imaging systems. The power detectors were designed in a 130 nm SiGe BiCMOS technology with f<sub>T</sub>/f<sub>max</sub> of 300 GHz/500 GHz. The initial detector design exhibits a measured peak responsivity of 80 kV/W and an estimated Noise Equivalent Power (NEP) of 0.4 pW/Hz<sup>1/2</sup> at 80GHz, respectively (the power consumption is 32 μW). Simulations of an optimised version of this detector design show that the performance could be even further improved in terms of achieving a higher sensitivity over a wider frequency range (NEP=0.3-0.4 pW/Hz<sup>1/2</sup> at 75-100 GHz). The presented SiGe detector circuits obtain a lower NEP in comparison with previously reported silicon based W-band power detectors and are competitive with InP based W-band detectors in terms of a higher responsivity and similar NEP.