Design and Optimization of Wideband Log-Periodic Dipole Arrays under Requirements for High Gain, High Front-to-Back Ratio, Optimal Gain Flatness, and Low Side Lobe Level: The Application of Invasive Weed

The design and optimization of wideband log-periodic dipole arrays (LPDAs) are presented in this chapter. The LPDAs are expected to simultaneously satisfy several requirements inside a wide operating frequency range. In particular, the optimized LPDA has to provide standing wave ratio (SWR) below a predefined value, gain values as high as possible, gain flatness (GF) below a desired value, both side lobe level (SLL) and front-to-back ratio (FBR) below a desired value, and all these requirements must be satisfied at the same time inside the entire frequency range of operation. Since the design problem is nonlinear and inherently multiobjective, the simultaneous realization of all the above requirements can only be achieved by applying global optimization algorithms. These algorithms are usually based on evolutionary optimization methods and have been proved to be capable of solving complex nonlinear problems with great success. Such an evolutionary method with high potential in antenna design is presented in this chapter. The method is called invasive weed optimization (IWO) and is applied in conjunction with the method of moments (MoM) to optimize LPDAs under the above-mentioned requirements. The MoM is a well-known full-wave analysis method and is utilized here to extract the radiation characteristics of the LPDA required by the IWO algorithm. Several design cases are studied concerning the LPDA geometry and the operating bandwidth. The derived LPDA geometries exhibit a behavior close to the desired one and therefore are able to enhance the performance of a wireless network in practical applications.