Broadband millimeter-wave planar antenna array with a waveguide and microstrip-feed network

In this paper, we describe a fixed-beam broadband planar antenna array at millimeter-wave frequencies. The antenna is fed by waveguide-feed and microstrip-feed networks. In order to ensure fixed beams and a broad bandwidth, a subarray concept is introduced. For efficient coupling, a novel waveguide-to-slot transition consisting of a slot pair and a narrow conductive bar is proposed. Simulated and measured bandwidth is found to be more than 7.1% from 40.5-43.5 GHz. The main beam directions are broadside over all frequencies. The maximum measured antenna gain is 30.2 dBi at 42.0 GHz.