Fig. 1. Schematic diagram of mixer signal transmission

Fig. 2. Schottky barrier diode structure (left) ^[1] and planar Schottky diode structure (right) ^[2]

Fig. 3. Schematic diagram of harmonic mixer (left)^[3] and top view of Schottky inverse parallel diode mixer (right)^[2]

Fig. 4. Energy band diagram (left) and I-V curve (right) of SIS junction^[5]

Fig. 5. Typical scheme of IF/DC signal connection for SIS mixer^[5]

Fig. 6. IF dependence of mixed signal intensity at temperature of 94 K^[7]

Fig. 7. Schottky diode equivalent model^[17]

Fig. 8. Schottky diode structure in terms of parasitic parameters (left) and diode material parameters (right)^[18]

Fig. 9. Structure of InP based Schottky diode

Fig. 10. Monolithic integrated HTS THz mixer equivalent circuit (left) and HTS THz mixer frequency response simulation (right)^[34]

Fig. 11. Josephson junction simulation equivalent circuit^[35]

Fig. 12. Schematic diagram of SIS mixer with integrated antenna, microstrip impedance converter, and superconducting junction (left) and S₁₁ curve for direct coupling of antenna and SIS junction (right)^[36]

Fig. 13. Geometry of double junction SIS tuned circuit^[37]

Fig. 14. Optical micrograph of NbN/AlN/NbN mixer with integrated tuning circuits (left) and DSB noise temperature as a function of LO frequency (right)^[43]

Fig. 15. Balanced mixer on wafer^[44]

Fig. 16. Diagram of balanced mixer device. (a) Balanced mixer device within waveguide mixer module; (b) signal path diagram of balanced mixer^[44]

Fig. 17. Optical micrograph of 0.5 THz all-NbN SIS mixer chip part^{(left) and receiver noise temperature and reduction in gap voltage versus bath temperature for SIS mixers (right) [45]}

Fig. 18. I-V curve, noise temperature, and IF characteristics of balanced SIS mixer.(a) Pump I-V curves for four SIS junction array when LO is 133 GHz; (b) measured noise temperature and IF as a function of bias voltage when LO is 155 GHz^[47]

Fig. 19. Schematic diagram of radiative coupling and temperature readout^[50]

Fig. 20. 100× optical magnification of HEB device graph (left) and schematic of cross-sectional structure of NbN HEB device (right)^[54]

Fig. 21. HEB mixer DSB noise temperature versus frequency^[55]. ‘o’, ‘□’, ‘+’ data are from Refs. [57-58]

Fig. 22. TRecDSB frequency data from different research groups^[14]

Fig. 23. Schematic diagram of various orientation angles of round bottom edge^[59]

Fig. 24. Photograph of mixer and junction area (left) and packaged mixer (chip 5 mm×5 mm) (right)^[62]