Low-Cost Center-Fed Slot Array Based on Gap Waveguide MLW Coaxial Line Technology for E-Band Automotive Radar

This article introduces an innovative center-fed slot array using multilayer waveguide (MLW) coaxial line technology. The array consists of three columns with eight in-line slots to narrow the beamwidth in the E-plane and H-plane, thus increasing the gain in the boresight direction. The slots are excited by the longitudinal currents created by a transverse electromagnetic (TEM) wave, which propagates within the coaxial line placed beneath them. Each column of the array is fed by a coupling slot placed in the center, thus mitigating beam squint over the operating frequency band. The aforementioned coupling slot directly couples the fields from an additional feeding line used for routing. The proposed design consists of six unconnected metal sheets which are stacked together. The use of gap waveguide technology prevents field leakage from any potential air gap among the layers, thus making assembly easier and more tolerant. A prototype with two side-by-side antennas is manufactured using a quick, cost-effective, and suitable for mass production metal sheet process. The measurements agree very well with the simulations within the frequency band of interest from 76 to 81 GHz. The measured return loss is better than 10 dB. Furthermore, the realized gain is around 16 dBi with 37° beamwidth in the E-plane and 16° beamwidth in the H-plane. In addition, the measurements of a back-to-back prototype show a loss of around 0.0179 dB/mm at 77 GHz for the coaxial transmission line. The properties of the radiation pattern make this element suitable for automotive long-range radar (LRR) applications.