Why normally you consider length of an antenna greater than lamda by 4?

The length of an antenna is often considered to be greater than one wavelength (λ) by about 4λ for certain designs, like those used in specific types of resonant or broadband antennas. This extended length helps to enhance the antenna's bandwidth and improve its radiation efficiency. Additionally, longer antennas can support multiple resonant frequencies, allowing for better performance across a range of frequencies. Ultimately, this design choice aims to optimize the antenna's operational characteristics.