79 GHz Multilayer Series-Fed Patch Antenna Array With Stacked Micro-Via Loading

A wideband compact series-fed patch subarray is proposed for 79 GHz multiple-input—multiple-output (MIMO) radar. The proposed subarray is, for the first time, loaded with stacked micro-vias (SMVs). Two sets of patches in the subarray are fed 180° out-of-phase. A low-cost, high-resolution multilayer printed circuit board (PCB) technology, called “any-layer PCB,” is used to implement the SMVs, which cannot be done by standard high-definition interconnect PCB technology. Moreover, the technology supports small SMVs on different layers; hence, thick machine-drilled vias can be avoided. For comparison, a series-fed patch subarray with no SMV loading is designed. It is shown that SMV loading facilitates a larger overlap of the impedance and gain bandwidths, leading to a larger operating bandwidth. The measured 10 dB impedance and 3 dB gain bandwidths are 15% and 9.6%, respectively. The sidelobe suppression is above 12.9 dB, and the maximum array gain is 12.67 dBi at 79.1 GHz. This subarray is suitable for MIMO radar, as its width is around half-wavelength and the SMVs around it mitigate the crosstalk between the transmitting and receiving arrays.