W-band Broadband Mixer

Broad-band integrated circuit mixer using fin line-coplanar waveguide (CPW) configuration with little difference was researched here. In the theory analysis of fin line, we used closed-form expressions to evaluate the normalized guide wavelength and characteristic impedance for the unilateral fin line and its variants. The fin line transition was the most important part of mixer design, the transition from unilateral fin fine to commensurate rectangular waveguide using sinusoid-squared taper contour were discussed next. The analytical expressions based on Quasi-static conformal mapping techniques were used here to determine the effective dielectric constant and characteristic impedance of CPW. The step discontinuity has also been analyzed next using hybrid finite element method and modeled as a T-network consisting of two series inductances and a shunt capacitance. The transition of unilateral fin line to coplanar waveguide, forming a frequency- independent 180 hybrid, is of fundamental importance in this construction. Using the Full-wave analysis based on the mode-matching technique was applied to analyze the scattering characteristics of this important transition.In the design and simulation of the mixer circuits, we used CST,HFSS and ADSsoftware. There were three transition lines in this configuration--fin line,SCPW,microstrip line. We built diode equivalent circuit of RF,LO firstly using Agilent ADS. In order to realize the broadband mixer in 3mm band more accurately and effectively, co-simulation of 3D field simulation software HFSS and CST was used. With this method, fin line to waveguide transition in RF and LO ports, mcrostrip line low pass filter, and the performance of entire circuits were optimized. The final result obtained is as follows:When LO frequency is in the 92.5GHz, LO power is more than 10mW, for the case of LO fin line backside, less than 11.5dB conversion loss for 27GHz RF instantaneous, IF bandwidth was achieved as the RF swept from 75-103GHz, and a minimum conversion loss of 7.54dB has been measured at 75GHz. The isolation between LO to RF is 22.2dB. For LO fin line facade, less than 12.8dB conversion loss for 28GHz RF instantaneous, IF bandwidth was achieved as the RF swept from 75-103GHz, and a minimum conversion loss of 8.47dB has been measured at 81GHz. The isolation between LO to RF is 24.9dB.Improvement is introduced in the end. As a key component of receive system, mixer plays an important role and it improves the performance of all system directly. The result discussed above is not the best performance of this integrated construction, more research effort is required next.