Showing papers by "Mohammed Abo-Zahhad published in 1998"
21 Jun 1998
TL;DR: In this paper, a multilayer dielectric film is used to filter the non-ired bands of a polychromatic beam using a digital filter, and the stop-bands are placed anywhere in the spectrum range by carefully choosing the thickness and the refractive index of each layer.
Abstract: In this paper, filtering nondesired bands of a polychromatic beam using multilayer dielectric films is described. The stop-bands could be placed anywhere in the spectrum range by carefully choosing the thickness and the refractive index of each layer. The total thickness of the structure, or the number of layers, affects the frequency response of the filter in such a way that increasing the number of coefficients of a digital filter or increasing the number of elements in an antenna array affects the respective responses. From computational point of view, reduction of computational time has been achieved by computing the characteristic matrix just once for similar layers. Illustrative examples are also given.
24 Feb 1998
TL;DR: In this article, a two-channel perfect reconstruction filter bank with rational transfer functions is presented, which is based on amplitude and phase correction of the main subband filters designed on amplitude bases.
Abstract: It is well known that filter banks that satisfy perfect reconstruction property can be obtained with selective linear phase FIR analysis and synthesis filters. The perfect reconstruction property guarantees that the filter bank is distortion less and thus the reconstructed signal is a delayed version of the input signal. Although they are less expensive and yield superior stopband characteristics, perfect reconstruction cannot be achieved with stable infinite impulse response (IIR) filters. IIR designs usually incorporate a post-processing equalizer that is optimized to reduce the phase distortion of the entire filter bank. This paper solves an open problem; namely how to construct a two-channel perfect reconstruction filter bank with rational transfer functions. A computationally simple method to obtain IIR analysis and synthesis filters that possess zero phase distortion is presented. The method is based on amplitude and phase correction of the main subband filters designed on amplitude bases. Conventional Butterworth, Chebyshev or elliptic amplitude based filters are used as decimated-interpolated analysis-synthesis filters. The amplitude and phase corrections are carried out by using a narrow band auxiliary channel which is neither decimated nor interpolated. The developed filter bank structure offers advantages in easy and flexibility of design as well as in less computational complexity compared to the conventional QMF banks with the same performances.