New configurations of small-size shielded metallic Fabry–Perot (FP) antennas with improved performance over a large frequency band are presented in <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$S$</tex></formula> -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 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\lambda_{0}$</tex></formula> and 2 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\,\times\lambda_{0}$</tex></formula> , 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 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$- $</tex></formula> 15 dB, and sidelobe levels lower than <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">${- }$</tex></formula> 20 dB have been obtained experimentally, over a wide frequency band (2.4–2.66 GHz). These characteristics make stacked FP cavity antennas very attractive to replace global coverage horn antennas, or to be used in feed clusters of multiple-beam antennas, especially in <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$C$</tex></formula> - and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$S$</tex></formula> -bands, where they lead to more compact and less bulky solutions compared to classical feed horns.