Discrete-Time Domain Techniques for the Design of Microwave Filters

• Main Authors: Da-Chiang Chang, 張大強
• Other Authors: Chin-Wen Hsue
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/08384288106818984466

博士 === 國立臺灣科技大學 === 電子工程系 === 89 === In this thesis, we propose an approach to design and implement networks with capability of being microwave filters.The basic idea is to form the networks by cascading serial and shunt transmission-line sections of unit electrical length. By using a proper variable transformation, we find that the transfer functions of such networks can be represented in the discrete-time domain as functions of z, which is equivalent to a unit of time delay. After some careful manipulation of the transfer functions, we can prove that the zeros of these transfer functions are fully characterized by the stubs of the networks. Besides, we find that the zeros of these transfer functions locate at the same region in the Z plane as the zeros of some well-known discrete-time filters. As a result, a novel approach making use of discrete-time signal-processing techniques and optimization methods is proposed to implement filters in the microwave frequencies. The design phase begins with the adoption of a discrete-time filter which satisfies the prescribed specifications. Based on the system function of the discrete-time filter, we can determine the pattern of the network according to specific rules and begin the implementation phase. The stub-related zeros of the transfer function of the network are then moved to the denominator of the system function of the discrete-time filter, and both functions are transformed into auto-regressive (AR) processes. The implementation phase is finally finished by using optimization methods to tune the values of the characteristic impedances of each transmission-line sections so that the coefficients describing both AR processes are as close to each other as possible in the minimum-square-error sense. This final step promises that the character of the transfer function of the network will follow that of the system function of the adopted discrete-time filter. To provide validation of the proposed approach, four types of filters are implemented by using microstrip line, namely, Butterworth low-pass filter, Butterworth band-pass filter, elliptic low-pass filter and inverse Chebyshev band-pass filter. The scattering parameters of all the networks are measured and compared with the ideal values to corroborate the approach presented in this thesis.