Fully Metallic Millimeter-Wave Mikaelian Lens Multibeam Antenna

This paper presents a compact fully metallic Mikaelian lens antenna with enhanced multibeam capabilities at 5G-N257 band for the first time. The lens is realized based on a parallel-plate waveguide (PPW) loaded with periodic metallic nails. The gradient equivalent refractive indices are relatively low with a profile from 1.0 to 1.6, realized by easy-to-process nails at millimeter-wave (mmW). An antireflection matching layer (ARML) with structure similar to the lens is added to the output edge of the lens, reducing the reflection caused by the steeply changing refractive index. In addition, a flare and several choke grooves are also employed along with the lens to further improve the radiation performance. Width-reduced asymmetric double-ridge waveguides are designed as multibeam feeders, supporting a ±30° beam scanning coverage with seven beams, overlap levels better than -4 dB and scan loss better than 2.4 dB. This mmW fully metallic Mikaelian lens multibeam antenna is fabricated with CNC machining and experimentally verified, providing a potential option for wireless systems requiring multiple channels.