Abstract-In the final step of any filter design process, the desired center frequency, coupling factor and external quality factor (Q ext ) are used to determine the physical parameters of the filter. Although in the most cases the physical dimensions of a single resonator for a given center frequency are determined using exact analytical or simple approximate equations, usually such simple equations cannot be found to easily relate the required coupling factor and Q ext to the physical parameters of the filter. Analytical calculation of coupling factor and Q ext versus dimensions are usually complicated due to the geometrical complexities or in some cases such as microstrip resonators due to the lack of exact solution for the field distribution. Therefore coupling factor and Q ext of various kinds of resonators, especially microstrip resonators, are related to the physical parameters of the structure by the use of time consuming full wave simulations. In this paper a surprisingly fast and completely general approach based on a soft computing pattern-based processing technique, called active learning method (ALM) is proposed to overcome the time consuming process of coupling factor and Q ext determination. At first the ALM technique and the steps of modeling are generally described, then as an example and in order to show the ability of the method this modeling approach is implemented to model the coupling factor and Q ext surfaces of microstrip open-loop resonators versus physical parameters of the structure. Using the ALM-based extracted surfaces for coupling factor and Q ext , two four pole Chebychev bandpass filters are designed and fabricated. Good agreement between the measured and simulated results validates the accuracy of the proposed approach.
Input impedance of microstrip patch antennas and coupling between array elements are very important, especially in active array design. There are several analytical and numerical methods reported to analyze this problem [5], [6], which are quite time consuming when good accuracy is required. Here in this paper, a qualitative model which is very fast and accurate based on fuzzy inference is presented [2], [3], and [4].General structure of the model is reviewed at first based on input impedance of a single patch. Then we explain the key definitions and the method we used to extract the parameters of the model. At first some measured or simulated data is required to extract its knowledge. Here we used both measured and HFSS simulated data. Variation of centers and radii, for partial loci, and biases and slopes, for partial phase lines, as input parameters of the fuzzy model, could be fitted by very simple curves. Then input impedance of microstrip patch antenna for any feed position can be predicted very easily by applying the initial values calculated from the above simple curves to proposed fuzzy system. To show the ability of the proposed modeling technique, coupling between two microstrip patch antennas is also modeled in a same way and its membership functions were extracted.
This paper presents analysis, design and simulation of a novel sub-wavelength metamaterial resonator and its application in designing miniaturized filters. The presented sub-wavelength resonator is a coaxial cylindrical cavity in which a combination of an ordinary dielectric material and a metamaterial layer has been inserted. The general dispersion relation for such a resonator is formulated. Using this general formula and considering the subwavelength scenario, the approximate dispersion relation is extracted. Based on this approximate dispersion relation and through the use of an anisotropic μ negative (MNG) layer, it is shown that this configuration may in principal exhibit an arbitrary low resonant frequency for a fixed dimension. In comparison with miniaturized rectangular cavities and also miniaturized one-dimensional resonators, the above mentioned resonator provides the possibility of selecting a distinct mode of operation and also a further degree of freedom in the approximate dispersion relation which brings more flexibility in designing miniaturized resonators. As an example design and simulation of a miniaturized coaxial cavity resonator together with the complete design of the anisotropic MNG layer are presented. The resultant cavity diameter is shortened by approximately 69% in comparison with theoretical minimum dimensions of a cylindrical cavity resonator of the same height. Finally based on the designed miniaturized resonator a miniaturized filter with the center frequency of 5.85GHz and the bandwidth of 20MHz is designed and simulated.
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