Surface‐acoustic‐wave guides have been obtained by ion‐implanting narrow channels on lithium niobate substrates. Guides of different widths have been tested at 150 MHz. Two doses of helium ions at 100 keV have been used. The acoustic power distribution profiles along a guide length close to 21 mm were determined by optical probing. Air‐gap silicon convolvers have been implemented with this kind of guide. An external figure of merit equal to −49 dBm has been measured, whereas without guidance the external figure of merit is only close to −61 dBm for the same transducer pattern.