Abstract: We describe a radiator unit for an antenna. The radiator unit is configured to radiate electromagnetic waves within a frequency band. The radiator unit comprises: a first radiating structure for radiating an electromagnetic wave having a first frequency within the frequency band, and a non-radiating structure coupled to the first radiating structure. One or both of (i) the first radiating structure comprises a first corrugation arranged on a first planar structure of the radiator unit, and (ii) the non-radiating structure comprises a second corrugation arranged on a second planar structure of the radiator unit.