Abstract: The invention concerns a broadband or multiband antenna for microwaves, comprising a reflector plane (R) and at least a radiating element (ER) arranged proximate to the reflector plane (R). A assembly of photonic forbidden band material default elements is superimposed on the reflector plane (R) and the radiating element (ER). Each photonic forbidden band material default element is substantially planar, parallel to the reflector (R) and has at least a characteristic of magnetic permeability of dielectric permittivity and/or thickness in the direction perpendicular to the reflector (R) different from one element of photonic forbidden band material to the next. The assembly forms a leaky resonant cavity. The invention is applicable to mobile telephone systems, or optical path transmissions.