A Millimeter-Wave Wideband Low-Sidelobe Slotted Antenna Array Based on a High Power Divider Ratio Microstrip Ridge Gap Waveguide Feed Network

This letter presents an 8×8 low-sidelobe waveguide slotted array antenna fed by a microstrip ridge gap waveguide (MRGW) feeding network. Two innovative approaches are adopted, by introducing a novel coupling-based unequal power divider, along with a broadband ±90° waveguide twist, to achieve a wideband low sidelobe performance for the array. The proposed power divider provides a 9.2 dB amplitude difference between its two output ports over a 24.5% bandwidth, with amplitude fluctuation within ±0.2 dB and phase difference maintained within ±5°. In addition, the ±90° waveguide twist not only simplifies the feeding network design but also obtains directional radiation. To validate the proposed approaches, a prototype array is designed, fabricated, and measured. The measured results demonstrate an impedance bandwidth of 27.5% (25–33 GHz) for |S11| < –10 dB, a peak gain of 20.4 dBi, and sidelobe levels (SLLs) below –20 dB in both E- and H-plane across the 25–32 GHz band.