Millimeter-wave Grating Spectrometer

Millimeter wave grating spectrometer is analyzed and discussed comprehensivelyin this paper.Diffraction efficiencies and resolving power of several reflecting gratings asfrequence-splitting component are analyzed in detail. Based on the theory of periodelectromagnetic system, diffraction efficiency formulas of the triangle grating,sinusoidal grating and rectangular grating are deduced used integral method, cubicspline approximation method and modal matching method respectively. The diffractionefficiencies are calculated by varying parameters of gratings and incidence angle. Twocomplex rectangular gratings are introduced. The formulas of the diffraction efficiencyare also deduced used modal matching method. After discussing the applicability of themodal matching method here, the comparison of diffraction characteristics between thecomplex gratings and rectangular grating is given. Angle dispersive ratio and resolvingpower of the gratings are also analyzed in detail. According to diffraction efficienciesand resolving power of the gratings, a triangle grating is selected used as thefrequence-splitting component, and parameters of the grating are given.Spherical reflectors and paraboloid reflectors as collimation and imagingcomponents are used abroad in the grating spectrometer. The focal region and the fieldintensity distribution of spherical reflector are calculated with the knowledge ofgeometry optics and stationary phase evaluation when a beam of parallel light isincident on a spherical reflector. The imaging characteristic is discussed when parallellight is incident in adaxial condition which is a special instance. The peculiarity that theparaboloid reflector hasn't spherical difference is proved. Abaxial spherical reflectorsare selected, and appropriate parameters are given after comparing collimation andimaging characteristics of the two reflectors.Finally, the grating spectrometer is designed. And measuring methods areintroduced for this system.It is a good reference for further research on high power millimeter wave and THztechnology.