A 77 GHz Planar Antenna Array in Four Layer Printed Circuit Board for Automotive Radar Applications

This paper presents the design of a 77 GHz antenna array system in four-layer printed circuit boards for automotive radar applications. Different substrates are utilized for the antenna array design where the top layer in 0.203 mm of thickness is the core material of RO-4003C with dielectric constant (DK) 3.55 and dissipation factor (DF) 0.0027 to meet millimeter wave requirements. The feeding structure in microstrip with 50 Ω of characteristic impedance is then miniaturized due to the thin substrate. Besides, the substrate-integrated-waveguide (SIW) is used for the power splitting function to reduce the parasitic radiation and the antenna array side-lobe level thereby can be suppressed. The second and third layer of substrates are in the prepreg and core materials of FR-4, respectively, with 0.203 mm for each layer to strengthen the mechanical support, where the worse DF in 0.021 does not affect the RF signal transmission because the copper foil as the ground plane isolates electromagnetic fields between the RO4003C and the FR-4 prepreg. The final design includes the launcher in grounded coplanar waveguide (GCPW), the SIW power divider, and a 4 by 4 microstrip antenna array. The simulation results show the operating frequency from 74.42 GHz to 79.28 GHz in lower than -10 dB reflection and the antenna gain of 14.6 dB,