Technical development of optimal methods for detection of simple gas-phase molecules using rovibrational or rotational spectra by the simultaneous detection of several spectral lines of a molecular band with the aid of a comb filter is considered. Two variants for implementation of the methods are based on a spectrometer with the echelle grating with a limited number of elements and Fresnel lens (mirror) with specific ring components that serves as a grating. The Fresnel filter can be matched with the parameters of optics of astronomic instrumentation in the absence of a decrease in the effective aperture.