The process of band expansion comes from a dual-band antenna pair and is based on characteristic modes theory (CMA). The multiple defective ground structure (DGS) is introduced for isolation enhancement. Another work has introduced a flexible method for designing a bandpass filter (BPF) using pixel structure and genetic algorithm (GA) optimization (contribution 19). The pixel structure is made up of a grid of metallic microstrip stubs, and the GA is utilized to determine the connections between these stubs. Furthermore, these designs are designed, fabricated, and measured with good trends between the outcomes, which support their ideas to be utilized in different wireless applications. We hope that this Special Issue on antennas and filters will offer readers a good overview of the current state-of-the-art developments in these fast-growing areas of research, as well as an introduction to some of the newest techniques developed in this field. **Conflicts of Interest:** The authors declare no conflict of interest. List of Contributions:
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