Achieving high directivity-bandwidth through flat GRIN superstrates in Fabry-Perot cavity antennas

The use of flat dielectric surfaces having a radial gradient of permittivity is investigated for use as superstrates in Fabry-Perot cavity (FPC) antennas. The use of such surfaces results in a varied reflectivity within the FPC and makes the boresight emissions spatially coherent. This results in a significantly enhanced gain-bandwidth product of a FPC antenna using only a single feed. The key advantage of such GRIN surfaces is their all-dielectric, flat and thin nature. A prototype FPC antenna is numerically investigated to study the feasibility of this concept. Half power directivity-bandwidth as high as 51% is recorded with peak directivity of 17.6 dBi.