A waveguide is a structure that guides electromagnetic waves especially in microwave frequencies. The geometry of a waveguide reflects its properties such as bandwidth (the second cutoff frequency to the first one), conductor attenuation, propagation characteristic, and power handling. The wide bandwidth and low conductor attenuation constant of waveguides are very important in many applications such as filters, couplers, and antenna arrays. Commonly used waveguides are of rectangular and circular cross sections. The bandwidth of circular and rectangular waveguides is 1.31 and 2.0, respectively, whereas the attenuation of circular waveguides is less than that of rectangular ones [1, 2]. After introducing the rectangular and circular waveguide, some researchers introduced a waveguide with complicated cross-section called as the ridged waveguide [3–13]. The ridged waveguides might have wider bandwidth than rectangular ones but their attenuation is much more than that of rectangular ones, instead. In this article, waveguides of nonuniform cross-section (called Nonuniform Waveguides) are introduced, analyzed, and optimized. The cross-section of these waveguide is optimized to achieve wider bandwidth than rectangular waveguides while lower attenuation than ridged ones. The waveguide cross-section is defined by using a Fourier series with unknown coefficients. These coefficients are optimized using genetic algorithm (GA) to reach a proper cross-section for waveguide. The finite difference method (FDM) and eigenvalue methods are used in analysis stage of optimization [14]. The results show that optimum designed nonuniform cross-section waveguides have lower conductor attenuation constant in comparison with double ridged waveguides of the same bandwidth.
