Small-Size Shielded Metallic Stacked Fabry–Perot Cavity Antennas With Large Bandwidth for Space Applications

New configurations of small-size shielded metallic Fabry–Perot (FP) antennas with improved performance over a large frequency band are presented in
$S$
-band for space missions. The bandwidth enlargement is obtained by stacking two FP cavities of different size, each of them presenting a low quality factor. Their radiating apertures measure around
$\lambda_{0}$
and 2
$\,\times\lambda_{0}$
, respectively. Concentric corrugations are also introduced between both cavities to control the higher-order modes that are excited systematically in shielded small-size FP antennas due to lateral resonances. The obtained results are compared to those of a single-stage FP cavity antenna with the same aperture size. Several prototypes have been fabricated and measured. An aperture efficiency higher than 70%, a reflection coefficient smaller than
$- $
15 dB, and sidelobe levels lower than
${- }$
20 dB have been obtained experimentally, over a wide frequency band (2.4–2.66 GHz). These characteristics make stacked FP cavity antennas very attractive to replace global coverage horn antennas, or to be used in feed clusters of multiple-beam antennas, especially in
$C$
- and
$S$
-bands, where they lead to more compact and less bulky solutions compared to classical feed horns.