Abstract: The new single-layer waveguide array antenna has many advantages, such as low loss, low profile, compact structure, and strong practicality. It has enormous application potential in millimeter-wave or even terahertz wireless communication fields and is currently a research hotspot. This paper first introduces the characteristics of various waveguide feed networks, points out the advantages of the E-plane waveguide feed network in millimeter-wave applications, and then describes the research on E-plane waveguides in single-layer parallel-fed waveguide array antennas and Butler matrix multibeam array antennas. Finally, the latest research progress on the application of open-ended waveguide radiating elements in single-layer waveguide array antennas as multi-bands and circular polarization is presented. This paper has reference value for the development of low-loss low-profile single-layer waveguide array antennas and their applications.