An end-fire -band flush antenna based on the branch-waveguide directional coupler

An end-fire flush antenna is made according to the principles of a branch-waveguide directional coupler, substituting open space for one of the waveguides. The remaining waveguide is partially filled with dielectric to make its internal wavelength equal to the free-space wavelength. Each radiating slot is a quarter-wave branch-waveguide whose thickness, relative to that of the main waveguide, controls the amount of radiation in a predictable manner that is noncritical as to frequency. An -band model with 40 slots has demonstrated the predicted gain of 19 db above an isotropic radiator, with sidelobe suppression exceeding 25 db and rearward suppression exceeding 35 db. The antenna lends itself to flush installation, making it particularly useful for aircraft and spacecraft applications.