| The transverse electromagnetic cell(TEM Cell)is an important device in the field of electromagnetic compatibility testing.As a traceability device for calibrating and measuring electromagnetic field sensors,it provides the basis for accurate measurement of electromagnetic fields.However,high-order modes limit the upper working frequency and testing space of the TEM Cell.This paper proposes a method of frequency-extending TEM Cell based on the principle of slot antenna and a transverse electromagnetic room spatial expansion method using the principle of virtual perfect electric conductor boundary,forming new TEM Cells.The specific work and major innovations are as follows:1.The characteristics of high order modes and field distribution in TEM Cell were deeply studied,and restricted conditions were partly modified.A method and index set for rigorous evaluation of the uniformity of electromagnetic field distribution in TEM Cell test area are proposed.The relationship between different measurement accuracy requirements and the size limit of the test object was established.It was found that the parameter error in the TEM Cell resonance frequency calculation method caused an error in the order of the resonance modes.The analysis summarizes the general conditions for extending the frequency band and test space used by TEM Cell.2.Using slot antenna theory,this paper studied the effect of surface slots on the suppression of high-order mode currents in TEM Cell,and obtained an optimized design method for surface slots.The ideal transmission mode in a TEM Cell is transverse electromagnetic wave,but high-order modes are generated in the high frequency and the electromagnetic field structure is disturbed,so its upper working frequency is the first higher-order mode frequency.This paper studies the mode of the electromagnetic structure of the standard TEM Cell,and analyzes the frequency of the first higher-order mode and the electromagnetic characteristics of the mode.In view of the lack of quantitative design methods for slots in conventional TEM Cell and the problems of multiple slots and high leak,the effects of single slots and slot arrays on the suppression of high-order mode energy are studied by using waveguide slot antennas and antenna array theory,and a method for surface slots on TEM Cell is proposed.Results show that the method of surface slots of the TEM Cell proposed in this paper can increase the upper working frequency of TEM Cell by 40%.3.By using virtual perfect electric conductor boundary conditions,a symmetric TEM Cell with multiplied test space is designed.The larger the test space of the TEM Cell,the easier it is to excite the higher order modes.Therefore,the upper working frequency limit of the TEM Cell also defines its maximum testing space.In this paper,electromagnetic field structure of single TEM Cell is analyzed.According to the mirror image principle,the method of multiplying testing space of TEM Cell by constructing the virtual perfect electric conductor boundary under differential excitation is studied.The paper simulates the design of quadruple extension of the TEM Cell,and carries out its physical processing and testing.Results show that new designs achieve the effect of multiplying testing space.4.A symmetric TEM Cell with surface slots is designed,as well as method for evaluating the performance of the extended TEM Cell based on the mixed-mode S parameter is proposed.In this paper,the combination of frequency extension and space extension method is proposed,and a new type of symmetrically extended surface slot binary TEM Cell structure is realized,and the upper frequency and test space of the TEM Cell can be extended at the same time.The paper also proposes an evaluation method based on mixed-mode S parameters,which breaks through the limitation that the standard S parameter cannot evaluate the symmetry of the TEM Cell.By measuring the mixed-mode S parameters of the symmetrically extended binary TEM Cell,the surface slotted symmetrically extended binary TEM Cell and the symmetrically extended quadruple TEM Cell,the new assessment method and the new design of TEM Cell are proved to be effective. |
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