Study Of Electromagnetic Coupling Through Apertures

The theory of electromagnetic coupling through apertures is studied in this paper. Firstly, MOM(method of moments) is introduced, then the processes of GNF(the generalized network formulation) for aperture problems and Characteristic Modes for aperture problems is given in terms of MOM.Secondly, singularity in Green function in surfaces is analyzed by eight-order approximate formulations of and using equal-volume sphere transformation,respectively and singularity in Green function derivative is solved by generalized function theory. Surface equivalent current of two apertures in conduction surfaces is calculated. In addition dipole model of the small aperture is developed. The near field of aperture is equivalent to quasi-static current,the far scatter field of it is equivalent to the scatter field of dipoles.Finally,the characteristic of generalized admittance matrix of a apertures-cavity structure is analysed by applying above methods. Expanding the scatter field of equivalent current in modes, and neglecting mutual-coupling between apertures, the generalized admittance matrix is equivalent to a two-port network according to network theory. Then the characteristics of transfer admittance and transmission cross section of the network are studied. It is found that for identical apertures the transmission cross section of the system at resonance is independent of the common radius of the apertures as well as the radius of the cavity. The transmission cross section is calculated.