We study the magnetoplasma excitations of field-effect-induced quantum-wire lattices with a unit cell that contains two closely spaced electron channels. The far-infrared-transmission spectra contain an additional mode that is not present in lattices with a simple unit cell investigated previously. We show with a classical model as well as by quantum-mechanical calculations that this mode can be explained by an interwire motion of the electrons that is characteristic for the double-wire system.