A Qualitative Model for Input Impedance and Coupling of Microstrip Patch Antennas by Means of Fuzzy Inference Method

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 [Deshpande, M.D., et al., 1982], [Pozar, D.M., 1982], 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 [Tayarani, M., et al., 2001], [Tayarani, M., et al.], and [Tayarani, M., et al., 1999]. 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.