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In this paper, a method for designing Chebyshev filters having flat group-delay characteristics in the main part of the passband is presented. From the general approximation theory, a method for obtaining the transfer function of Chebyshev filters with complex transmission zeros is derived, which are so determined that the group-delay characteristics may be flat in the main part of the passband. A new theory of cascade synthesis, which is an extension of Belevitch's cycle, and an extended bisection theorem are introduced. By the applications of these results, Chebyshev filters with flat group delay can be realized. A practical design example is also included.