The Elliott’s procedure for the design of planar waveguide arrays of longitudinal slots has been extended to the cylindrical conformal case. The presented procedure has been devised to deal with the most general case of a cylindrical conformal substrate integrated waveguide (SIW) longitudinal slot array with a dielectric cover. Both external and internal mutual coupling have been accurately and effectively taken into account. The results of the synthesis procedure have been validated using both Ansys HFSS simulations and experimental results, showing a good agreement with the design specifications.