A 77-GHz Low-Conversion-Loss Fourth-Harmonic Mixer on SISL Platform

This letter presents a 77-GHz low-conversion-loss (CL) fourth-harmonic mixer based on the substrate-integrated suspended line (SISL) platform. Based on the traditional stub-type harmonic mixing structure, we add several additional transmission lines, which will participate in the impedance matching of the diode together with stubs to reduce the CL. A 3-D electromagnetic (EM) diode model is established for accurate simulation at millimeter-wave frequency. The presented SISL mixer was fabricated by the low-cost printed circuit board (PCB) process and was self-packaged in FR4 substrates. When the local oscillator (LO) frequency is 19.45 GHz and the radio frequency (RF) is 78 GHz, the minimum CL is 12.2 dB under an LO input power of 12 dBm. This mixer is suitable for 77-GHz automotive anti-collision radar systems.