Method for Computing the Resonator Q and Effect of Grid Arrangment and Coarseness on the External Q in the FDTD Method (Special Issue on Computational Electromagnetics)
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概要
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A new method for computing the external Q and unloaded Q of a resonator in the time domain is proposed. The external Q and unloaded Q are derived from the input energy, the field amplitude at the observation point within the resonator and the output power from the port, using the energy relationship during the early stage of the amplitude growth process of the electromagnetic field in the resonator excited by a sinusoidal wave. First, this energy method is applied on the rectangular cavity without a port to carry out a comparison with the analytically derived exact solution. Over the wide range of surface resistances, the unloaded Q can be obtained with an error on the order of 0.01 percent. It is also shown that even if Q is as high as the twelfth power of ten (10^<12>), one is still able to do the calculations with the computation time corresponding to 230 cycles of the resonant frequency. Next, the method is applied to the rectangular cavity with apertures, and the external Q and unloaded Q are computed. Based on these results, the validity of the Q computation is confirmed. This paper also reports the effects of the arrengement types and coarseness of the FDTD grid on the external Q. The rectangular cavity with inductive apertures is computed using the FDTD method. Two types of grid arrangements are used for the coarse, fine and graded meshes. When comparing the external Q's, we found considerable differences between the results obtained when using the type 1 and 2 grid arrangements, while the difference in resonant frequencies was about 0.1%. It is satisfactory to consider that less power flows out through the aperture in the type 1 arrangement than the actual power flow, while more power flows out in the case of type 2. These facts are important when modeling the conductor corners.
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- 1998-12-25