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超导HEB(Hot Electron Bolometer)热电子混频器是1THz以上灵敏度最高的相干探测器,为了进一步提高其灵敏度,有效减小射频信号在传输路径中的损耗,实现超导HEB混频器的超宽带混频功能,设计高耦合效率的射频匹配电路尤为重要。首先提出了混频器耦合电路的理论模型,然后采用三维电磁场仿真软件HFSS和类似于准光学天线的集总源法,设计了一种超宽带、低损耗的太赫兹信号耦合电路,对超导HEB混频器的嵌入阻抗在整个0.9～1.3THz的工作频带范围内进行了详细的分析。系统研究了低通滤波器中高低阻抗线结构,波导到微带转换中存在的高次模对射频信号传输的影响,并模拟仿真了实验中可能出现的磨片厚度误差对嵌入阻抗的影响。分析结果表明,该混频器的嵌入阻抗为35Ω-j10Ω左右,在整个工作频带内变化缓慢,能够实现超宽频带匹配,混频器的相对工作带宽可达到36%,仿真结果和理论模型计算结果完全一致。该研究结果对研制超宽带高灵敏度的超导HEB混频器具有很好的指导意义。
Hot Electron Bolometer The hot electron mixer is a coherent detector with the highest sensitivity above 1THz. In order to further improve its sensitivity, it can effectively reduce the loss of the RF signal in the transmission path and achieve ultra-superconducting HEB mixer’s super Broadband mixing function, the design of high coupling efficiency of the RF matching circuit is particularly important. Firstly, the theoretical model of mixer coupling circuit is proposed. Then, an ultra-wideband and low-loss terahertz signal coupling circuit is designed by using three-dimensional electromagnetic field simulation software HFSS and lumped source method similar to quasi-optical antenna. The embedded impedance of the HEB mixer is analyzed in detail over the operating frequency range of 0.9 to 1.3 THz. The effects of the high-order modes existing in the low-pass filter on the low-impedance line structure and the waveguide-to-microstrip transition on the RF signal transmission were systematically studied. The influence of the thickness error on the embedded impedance in the experiment was simulated. The analysis results show that the mixer’s embedded impedance is about 35Ω-j10Ω, which changes slowly in the whole working frequency band and achieves ultra-wide band matching. The relative working bandwidth of the mixer can reach 36%. The simulation results and the theoretical model calculation The result is exactly the same. The results of this study are very helpful for the development of ultra-wideband high-sensitivity superconducting HEB mixers.