Abstract: The work is devoted to evaluation of spatial spectral density of the power of an electromagnetic wave radiated by a lower hybrid grill - multiple waveguide which is preceded by an EM wave source at the so-called lower hybrid frequency. We consider the simplest grill model. The waveguides are supposed to be infinitely high with identical transverse size. We also consider the simplest model for the impedance of plasma surface layer. The core of the work is the optimized numerical programm devised for evaluation of the spectra - in the Fortran language, standard 90 and higher. Using it we find spectra for different plasma parameter values.