Broadband Small-Aperture High-Gain Ridge Horn Antenna Array Element

This letter presents the design and characterization of an octave-bandwidth, small-aperture, linearly polarized, high-gain horn antenna operating in the 6–12 GHz band for active arrays. The aperture size is limited by the waveguide feed cutoff at lower frequencies and by grating lobes at higher frequencies. The radiating structure is composed of an E-plane flared horn with an exponential double ridge fed by a low-loss waveguide-to-microstrip transition, eliminating the need for additional connections between the antenna elements and the beamforming and amplification circuits. The horn is loaded with an artificial dielectric with 1 
$< \epsilon _{\mathrm{r,eff}}< $
 2.2, which lowers the cutoff frequency and improves phase distribution over the aperture. The lens and feed loading structure are designed together to improve matching without degrading the radiation pattern. A prototype is fabricated in brass using split-block machining, and the lens is machined from 16 parallel dielectric slabs. The measured performance is in agreement with simulations.