In a mixer, when a baseband signal with a phase \(\theta\) is multiplied by an LO signal with the same phase \(\theta\), the resulting output signal has zero phase. This implies that if the baseband signal phases (I, I45, Q, and Q45) are matched to the corresponding LO signal phases (I, I45, Q, and Q45), all components align with zero phase at the mixer output and add constructively, resulting in a 4x gain (check HRM mixer to see math). However, if the baseband signal is DC, it has no phase i.e., only a magnitude that can be positive or negative. When DC signals multiply with LO phases (I, I45, Q, and Q45), the resulting output signal inherits the phase of the LO signals. Consequently, at the mixer output, you observe four vectors corresponding to the LO phases (I, I45, Q, and Q45). To analyze this, we sum these vectors to determine the resultant vector. By comparing this resultant vector with the signal vector, we can calculate the LO leakage. The calculator below performs this computation.