## 3 Results  
At \(\rm V_{DD}=0.8\) V and \(\rm V_{D1}=\rm V_{D2}=\rm V_{G1}=\rm V_{G2}=0.4\) V, the down-conversion mixer dissipates 6.5 mW, close to the simulated one (6.4 mW). The on-wafer S-parameter measurement of the mixer was conducted using a Keysight N5245B four-port PNA network analyzer (0.01-50 GHz). Figure 7a shows the measured and simulated RF-port reflection coefficient (\(\rm S_{11}\)) of the mixer. The mixer achieves a measured minimum \(\rm S_{11}\) of \(-34.6\) dB at 40 GHz and \(\rm S_{11}\) better than \(-10\) dB for 20.4-44.2 GHz (i.e., \(\rm f_{10 dB}\) of 23.8 GHz), close to the simulated result (minimum \(\rm S_{11}\) of \(-32.9\) dB at 39 GHz and \(\rm f_{10 dB}\) of 22.8 GHz (21.7-44.5 GHz)). For a mixer or amplifier using series RLC resonance matching, its \(\rm f_{10 dB}\) (50/(3\pi L_{in}\)) in theory) is inversely proportional to the input inductance \(\rm L_{in}\) [14; 15]. For the differential RF inputs, \(\rm L_{in}\) (i.e., sum of the inductance of \(\rm TL_{1}\) and \(\rm TL_{2}\)) is 435 pH, equivalent to \(\rm f_{10 dB}\) of 12.2 GHz. The wideband \(\rm S_{11}\) of the mixer is attributed to the wideband matching between the RF-balun outputs and the RF inputs due to the small \(\rm L_{in}\) at RF inputs. Figure 7b shows the measured and simulated IF+ port reflection coefficient (\(\rm S_{33}\)) of the mixer. The mixer achieves a measured \(\rm S_{33}\) better than \(-10\) dB for 0-10.2 GHz (i.e., \(\rm f_{10 dB}\) of 10.2 GHz), close to the simulated one (\(\rm f_{10 dB}\) of 15.1 GHz (0-15.1 GHz)). The wideband \(\rm S_{33}\) is attributed to the \(\rm Z_{in}\) matching at low frequency (LF) since the design values of \(\rm R_{49}\)\(\rm lR_{4810}\)\(\rm lR_{f}\) and \(\rm R_{4811}\)\(\rm lR_{4812}\)\(\rm lR_{f}\) are 50 \(\rm\Omega\). The slight deviation of the measured \(\rm S_{11}\) and \(\rm S_{33}\) (from the simulated  
Figure 6: Simulated (**a**) AI and PD of balun-2, and (**b**) \(\rm S_{11}\), LO–RF isolation, CG, and NF of the down-conversion mixer. ones) of the down-conversion mixer is mainly attributed to the substrate- and layout-layer parameters provided by the foundry being not accurate enough at mm-wave frequencies. Figure 8a shows the measured and simulated LO-RF and LO-IF isolation versus LO frequency characteristics of the mixer. The mixer achieves measured LO-RF isolation of 46.1 dB at 28 GHz and 41.6-55.9 dB for 0-50 GHz, close to the simulated one (44.9 dB at 28 GHz, and 40.3-62.4 dB for 0-50 GHz). Since the Miller capacitance (of C\({}_{\text{gd}}\)) at D1/D2 of M\({}_{1}\)/M\({}_{2}\) has been taken into account in the C\({}_{\text{d}}\) calculation, the decent LO-RF isolation is attributed to the symmetrical layout of the mixer core, and unilaterilization of the C\({}_{\text{gd}}\) effect of M\({}_{1}\)/M\({}_{2}\). Moreover, the mixer achieves measured LO-IF isolation of 39.9 dB at 28 GHz and 36.6-82.7 dB for 0-50 GHz, close to the simulated one (43.3 dB at 28 GHz, and 36-84.8 dB for 0-50 GHz). The decent LO-IF isolation (especially at LF) is attributed to the symmetrical layout of the mixer core and the inclusion of C\({}_{\text{by}}\) between M\({}_{3}\)/M\({}_{5}\) and M\({}_{9}\)/M\({}_{10}\) (and M\({}_{4}\)/M\({}_{6}\) and M\({}_{11}\)/M\({}_{12}\)) for low-pass filtering of the LO leakage. In brief, LO leakage around f\({}_{0}\) is suppressed by C\({}_{\text{by}}\). Therefore, LF (around DC) leakage at the IF output is minimized due to the effective suppression of the second-order nonlinearity of the CCPT-RL-based core IF load and the output buffer amplifiers. Figure 8b shows the measured and simulated CG versus LO\({}_{\text{in}}\) characteristics of the mixer at 28 GHz. Intrinsically, the mixer is a nonlinear multiplier. Hence, it is reasonable that the CG of the mixer increases with the increase in LO\({}_{\text{in}}\) until saturation of the LO switch transistors (i.e., close to perfect switch operation).