Study Of The Scattering Characteristics Of Metallic Wire Grids At Submillimeter Wavelengths

Metallic wire grids are widely used in millimeter- and submillimeter-wavequasi-optical systems (Fourier Transform Spectrometer, for example). They areused as polarizers and beam splitters. In general, ideal transmission model andmicrowave transmission line model are used to analyze the transmissioncharacteristics of a metallic wire grid. In a compact Fourier TransformSpectrometer, the diffraction effect of an electromagnetic wave by a metallic wiregrid must be included. In this dissertation the scattering characteristics of aGaussian electromagnetic beam incident on a metallic wire grid is mainly studiedby applying electromagnetic theory, and the numerical calculation, the simulationand the experiment are used to analyze nearly field scattering characteristics of ametallic wire grid. The two-dimension scattering characteristics of a Gaussian electromagneticbeam by a cylindrical conductor are studied. A Gaussian beam is expanded intothe sum over a set of plane waves with the aid of the plane-wave spectrumtechnique. The scattering formulae of a Gaussian electromagnetic beam by acylindrical conductor are acquired by using addition theorem and conductor'sboundary conditions. In addition, three-dimension scattering characteristics of aplane wave by a cylindrical conductor are described by applying reduced matrix. Microwave transmission line model on a cylindrical wire grid is discussed.The two-dimension scatterings formulae of a plane wave by a cylindrical wiregrid are derived by using coordinate displace Floque theorem and linearityaddition theorem. The power reflection coefficient of a plane wave by acylindrical wire grid in zero-order diffraction is calculated and compared withthe result that acquired from microwave transmission line model. In addition,three-dimension scattering characteristics of a plane wave by a cylindrical wiregrid are described by applying reduced matrix. Expanding a monochromatic electromagnetic beam into the sum over a seriesof plane waves using the spectral representation technique derives the generalforms of the scattering formulae of a monochromatic electromagnetic beamincident on wire grids. The general forms of the scattering power formulae of amonochromatic electromagnetic beam by wire grids are presented by usingPoynting theorem. The two-dimension scattering formulae of a Gaussian electromagnetic beam bya cylindrical wire grid are studied. The scattering formulae and the powerreflected and transmitted coefficients of a Gaussian electromagnetic beam by acylindrical wire grid are directly derived with the aid of the plane-wave spectrumtechnique. The results are compared with those acquired from a plane waveincidence. The reflection and transmission characteristics and effects of evanescentspace-harmonics on their characteristics of a Gaussian electromagnetic beam innear field by a cylindrical wire grid are studied and compared with thoseacquired from a plane wave incidence. The output power distribution of a Gaussian electromagnetic beam by acylindrical wire grid is measured using an experimental setup maded of a500GHz Phase-Lock-Loop (PLL) source and compared with the theoreticalcalculation value. The measurement result confirms the theorical analysis.