In this paper, classical rat-race coupler based on coplanar stripline is presented. It was built using BiCMOS 55nm technology. Parametrical analysis targeting the position of additive compulsory dummies from the coplanar stripline is carried out. Two versions of the rat-race couplers are compared: without and with metallic dummies. Simulation results show that isolation and reflection coefficients are preserved under 20 dB. With dummies considered, insertion loss value is 4.2 dB at 118 GHz. With the addition of metallic dummies 2 GHz downshift in coupler performance is noticed. Maximum amplitude imbalance is 0.4 dB reported at 140 GHz. Phase imbalance difference between both cases doesn't exceed 3.1° for the whole bandwidth of interest. Between coupled and through ports 181.8° is the value of the phase difference.