Design of 3dB directional coupler for millimeter wave radar

This paper presented three types of 3dB directional couplers designed for millimeter wave radar with a center frequency of 79GHz and operating frequency range of 77 GHz⁓81 GHz. The characteristic impedance of microstrip line for these three directional couplers was obtained using the odd-even mode analysis method, and their design parameters were calculated accordingly. Models of the directional couplers were established and simulated using HFSS simulation software for analysis. The simulation model diagrams were optimized, and the final simulation results were obtained. The final results showed that all three types of 3dB directional couplers had good isolation performance. A comparison of the coupling effects of the three directional coupler was provided, showing that the microstrip hybrid ring directional coupler offered better coupling effects and was more conducive to fabrication.