A Two-phase Full-wave GA Optimization for W-band Image Rejection Waveguide Filter Design An-Shyi Liu*, Ruey-Beei Wu, and Yi-Chun Yu Department of Electrical Engineering and Graduate Institute of Communication Engineering National Taiwan University Taipei, Taiwan 106, R.O.C. Address: No. 1, Sec. 4, Roosevelt Rd. Taipei, 10617, Taiwan, ROC. E-mail: rbwu@ew.ee.ntu.edu.tw 1. Abstract The feasibility of a new two-phase design approach for image rejection waveguide filter using a genetic algorithm is demonstrated in this paper. The design approach is capable of minimizing the number of simulations required in the full-wave analysis, without sacrificing the accuracy of final design. In addition, it has been employed for a high-pass waveguide filter design at W-band and yields a satisfactory performance. 2. Introduction Conventional synthesis procedure for waveguide transformer [1] had been investigated, however, the performance isn’t satisfactory [2]. Otherwise, mode matching technique [3] with quasi-Newton method [4], which is not computationally intensive and requires a good initial guess, had been employed for waveguide filter design. In order to avoid the dependence on starting point, stochastic methods, such as genetic algorithms(GAs) [5], are more suitable. In this paper, a two-phase full-wave GA optimization for waveguide filter design approach is proposed. To begin with, the waveguide filter is modeled as cascaded transmission lines and then the waveguide H-plane dimensions are optimized by a GA. The E-plane dimensions of waveguide sections are assumed to be in a linear variation, for which the best linear coefficient is determined from full-wave analysis [6]. The approach had been applied to design an image rejection waveguide filter at W-band and both the simulated and measured results are demonstrated in this paper. 2. Statement of the problem Fig. 1(a) shows the configuration of a symmetrically double-plane stepped rectangular waveguide filter. Several waveguide sections of width A i , height B i , and length C i (i=1,…,2N-1) are inserted into standard waveguide with A 0 =A 2N =2.54 mm. Figs. 1(b) and 1(c) show the dimensions in H-plane and E-plane, respectively. The design specifications are listed in Table I.