Study On LTCC-based Sub-harmonic Mixer For Mmw Velocity-measuring Radar

A detecting system of millimeter-wave coherent Doppler continuous-wave radarfeatures high measuring accuracy, thus it has been widely used. As one of keycomponents of the system, millimeter-wave mixer’s performance is directly related tothe performance of radar system, therefore it receives much attention.The use of sub-harmonic mixer can effectively reduce the local oscillator’s (LO’s)operation frequency, thus reducing the difficulty of developing high frequency LOs,which further reducing the system’s difficulty and cost.In this thesis, we analyzed a millimeter-wave sub-harmonic mixer for continuous-wave radar measuring system. Combined with advantages of low temperature co-firedceramic (LTCC) technology, we designed passive networks of sub-harmonic mixerwhich works on30GHz band. The mixer has following characteristics:1. By using second sub-harmonic mixer, the LO frequency is halved, which reduces thedifficulty and cost of LO’s design;2. Based on the detecting system, a harmonic oscillator is used. It provides thefundamental frequency and harmonic signals. The fundamental signal is filtered out todrive the mixer, while the harmonic signal is applied to antenna, which sufficientlyutilizes the LO’s signals;3. A novel over-coupled directional coupler using LTCC technology is presented, whichcan realize high isolation between RF and LO signals as a result of high isolationbetween input ports.4. A compact microstrip resonant cell (CMRC) using LTCC technology is designed inthis thesis. It can reduce entire size of the circuit compared with traditional Hi-Lomicrostrip low-pass filter.The mixer is designed and simulated using field simulation software HFSS andcircuit simulation software ADS. The coupler is designed and produced individually,and its insertion loss at15GHz is less than0.9dB. The mixer’s conversion loss can beless than5dB when the LO input power is7dBm.As a key component of radar system, the mixer plays an important role and it improves the performance of whole system directly. This thesis presents a meaningfulreference on millimeter-wave mixer researches.