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-degrees out-of-phase. A low-cost, high-resolution multilayer PCB technology, called “Any-Layer PCB”, is used to implement the SMVs, which cannot be done by standard HDI 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 1/2-wavelength and the SMVs around it mitigate the crosstalk between the transmitting and receiving arrays.