Measurements of the prototype agreed with simulations well; the plots below show the theoretical co-polarization (solid) and cross-polarization (dashed) in blue and the corresponding measured patterns in red. The insets on the upper right of each plot show the corresponding electric field distribution in the metahorn aperture. The minor differences and asymmetries in the cross-polarization patterns can be attributed to manufacturing imperfections. Future prototypes will incorporate metamaterials based on printed circuit boards, which allow for much more accuracy and precision in manufacturing than soldered wires, as well as lower cost.

We have also investigated metamaterials satisfying the balanced hybrid condition, to be used in a conical Ku-band horn antenna. For this design, the metamaterial is based on a printed circuit board with vias connecting patterned conductive patches on the top surface to the ground plane on the bottom surface of the board. The following figure summarizes the results of the theoretical study. Note that the product of the surface impedances is approximately unity across the band; i.e. the metamaterial satisfies the hybrid-mode condition (upper left). Again, this is a dispersion-engineered low-index metamaterial with negligible loss (upper right). As one would expect from a hybrid-mode horn, both sidelobes and cross-polarization are extremely low (bottom two plots).

This performance can already be obtained over sub-octave bandwidths using corrugated horns, but this approach would provide the same performance over a comparable or broader bandwidth. Moreover, this approach would be significantly less expensive to manufacture and would require much less mass than corrugated horns, which is critical for satellite applications.