Improved-Performance Horn Enabled by Inhomogeneous Metasurfaces
Motivation and Rationale
The dual-polarized square horn in the previous section is eminently practical for fabrication, but a metahorn with a circular profile could lead to even broader operating bandwidths. This behavior results from the corner areas of rectangular horns where the balanced hybrid condition cannot be met, causing differences in the higher- order modes supported by square versus circular waveguides. This section, while remaining as practical as possible, focuses on what would be necessary to maximize the potential of metahorn technology.
The unit cell geometry employed for this section is related to the wire-grid structure shown previously, but it is intended for printed circuit manufacturing like the pixilated unit cell designs. Figure 2.17a shows the unit cell structure, with a patch serving as an end-load above a conducting via and a continuous strip of copper connecting all unit cells in the x-direction. The rectangular patch width and length provide a simple means for adjusting the metasurface properties depending on position within the horn, analogously to corrugations of varying depth acting as mode converters in conventional corrugated horns. The unit cell periodicity and thickness were fixed to be p = 3 mm and t = 5.2 mm, respectively, leading to operation between approximately 10 GHz and 20 GHz, including the Xu-band. The transverse connecting wire was set at a width of 0.4 mm. Fixing these parameters allows for more practical manufacturing and application to a horn antenna's interior.