A polarizing reflector for broadband antennas and for converting a same linear polarization into a given circular polarization handedness over one frequency band when operating in a single wideband at normal incidence illuminated by a plane wave, or into a first given circular polarization handedness over a first frequency band and into a second handedness over a second frequency band, the first and the second circular polarization handedness being substantially equal or orthogonal when operating in dual-band at normal incidence illuminated by a plane wave, the polarizing reflector comprising a flat dielectric substrate (4; 214) delimited between a first surface (12; 222) and a second surface (14; 224), having a thickness h and a dielectric permittivity ε r, a patch array layer (6; 216) formed by a first bi-dimensionally periodic lattice (16; 226, 230) of thin metallic patches (18; 228) on the first surface (12; 222) of the substrate (4; 214), the periodic lattice (16; 226, 230) having a first set (22; 232, 234) of patch rows (24; 236, 238) oriented along a first direction x with a periodicity d x and a second set (26; 242, 244) of patch columns (28; 246, 248) oriented along a second direction y with a second periodicity d y, a ground layer (8; 218) formed by a plain metallic layer on the second surface (14; 224), located below the patch array layer (6; 216); the substrate (4; 214) separating the patch array layer (6; 216) and the ground layer (8; 218), and all the patches (18; 228) having a same shape elongated along the second direction y and forming electric dipoles when electrically excited along the second direction y, the polarizing reflector being characterized in that for each row (24; 236, 238), the patches (18; 228) of the said row (24; 236, 238) have and are all crossed by an elongated metallic strip (32; 252, 254) oriented along the first direction x and having a width c, the elongated metallic strip (32; 252, 254) forming one and a same integral piece, or the patches of the said row are mutually separated and all lined along the first direction x by two elongated metallic strips, each metallic strip having a width c and forming one and a same integral piece, and the geometry of the patch array (6; 216), the thickness h and the dielectric permittivity ε r of the substrate (4; 214), and the geometry of the elongated metallic strips (32; 252, 254) are configured so that the patch array (6; 216) including the elongated metallic strips (32; 252, 254) induces a fundamental aperture mode and a complementary fundamental dipolar mode along two orthogonal TE and TM polarizations within the single frequency band when operating at normal incidence in a single wide band or induces a fundamental aperture mode and a first complementary fundamental dipole mode along two orthogonal TE and TM polarizations within the first frequency band and the fundamental aperture mode and a second complementary higher order dipole mode along the two orthogonal TE and TM polarizations within the second frequency band when operating in dual wide band, the differential reflection phase between the two fundamental aperture and dipole modes over the single band, or the differential reflection phase between the two fundamental aperture and dipole modes over the first frequency band and the differential reflection phase between the fundamental aperture and a higher dipole mode over the second frequency band being equal to ±90° or to an odd integer multiple of ±90°.