Validation of Lower Hybrid coupling codes (Brambilla, GRILL3D-U,TOPLHA) with the FTU conventional grill

design were continuously pursued in view of ITER severe edge conditions. The excitation of LH waves by means of a phased waveguide array was initially proposed in 1974 by Lallia. A systematic study of the coupling problem related to this launching structure was firstly done by Brambilla in 1976 under the so-called grill theory. Subsequently, more detailed analyses were performed, still adopting several approximations in order to simplify the problem, such as the absence of mode conversion and 2D antenna models. The following studies developed more sophisticated models, for instance taking into account new antenna concepts, fast wave excitation, finite poloidal dimensions, etc. At the same time, numerical tools implementing theoretical models were developed; they were essentially based on mode matching technique, single-pass approximation and a slab plasma model. From the antenna viewpoint, the first codes could handle very simple antenna geometries, which then considerably increased in complexity. Lately, due to remarkable developments in computational electromagnetic techniques, new codes, totally or partially based on full-wave antenna solvers, appeared too. This paper validates three LH coupling codes based on different solving techniques: TOPLHA, GRILL3D-U, Brambilla code. They have been run to compute the coupling between the LH waves, launched by a row of the independently phased waveguide array antenna (conventional grill), and some FTU plasmas. TOPLHA and GRILL3D-U have been already compared with another well-established code, i.e. ALOHA, in the frame of the EFDA task HCD-08-03-01, where the LH antenna, proposed for ITER, was used as benchmark. Furthermore a validation of TOPLHA, GRILL3DU and the Brambilla code has been recently done as regards to the FTU conventional grill in terms of average reflection coefficients. In this paper a more detailed analysis is presented by comparing simulated curves with experimental data, that refer to the reflection coefficients effectively measured at the antenna mouth by built-in directional couplers.