Search

The adaptive neuro-fuzzy inference system (ANFIS) has been widely used for modeling different kinds of nonlinear systems including RF power amplifiers (PAs). The modified ANFIS (MANFIS) architecture is simpler than that of ANFIS, but with nearly the same performance for modeling nonlinear systems. In this paper, the MANFIS is applied to model RF PAs with memory effects. The simulation and experimental results both in the time and frequency domains show that this model has good modeling accuracy and the characteristics of faster convergence and lower computational complexity compared with the ANFIS model. The normalized mean squared errors of the MANFIS model are slightly lower than those of some other neural network models such as the real-valued time delay neural network, radial basis-function neural network, etc. Finally, the MANFIS model is successfully used in a digital predistortion system, which can provide over 10-dB adjacent channel leakage ratio improvement for three-carrier wideband code division multiple access signals. Index Terms--Adaptive neuro-fuzzy inference system (ANFIS), adjacent channel leakage ratio (ACLR), digital predistortion (DPD), power amplifiers (PAs).

In this paper, a generalized absorbing boundary condition (Z-ABCs) is constructed in the Z-transform domain. Based on Z-ABCs, some well-known ABCs, such as the Mur's ABC, the dispersive boundary condition, Zhao and Litva's ABC, Liao's ABC, etc. can be easily deduced. Besides, it can also result in some new ABCs. Recurrence formulas for the coefficients of Z-ABCs are presented, and the stability and numerical dispersive characteristics are discussed in detail. In order to validate the Z-ABCs, the finite-difference time-domain method is applied to the analysis of transmission lines, integrated filters, patch antennas, and scattering problems. Index Terms--Absorbing boundary condition (ABC), electromagnetic, finite-difference time-domain (FDTD) method, numerical dispersive, stability, Z-transform.

The absorbing boundary conditions (ABC's) are essential to terminate the computational space when the finite-difference time-domain (FDTD) method is applied to analyze electromagnetic (EM) problems. With the ABC's, the fields on the truncated boundaries are evaluated by the interior fields. In this paper, the relationship between the fields on the terminated boundaries and the interior fields is expressed as the transfer functions in the Z-domain. The proper transfer functions are determined from the radiation condition or the transmission condition. Simplifying these transfer functions into rational functions, we obtain different schemes of the ABC's. In this paper, both the transfer functions and coefficients of the final ABC's are derived and expressed as recurrence formulas for the convenience of programming. This method has the property of simplicity and flexibility. The ABC's obtained by this method show good absorbing performance and numerical stability in the practical applications. Index Terms - FDTD methods.