“…However, it is important to note that the subwavelength periodicity is the most flexible approach as it can be easily integrated with other approaches such as the element rotation, the multi resonance or phase delay lines to yield superior gain bandwidth characteristics as it will be discussed in subsection F. In this approach the majority of the designs operate in X-band [73], [93], [96], [97], [98], [99], [101], [102]. There are one K-band designs [104], three Kuband wideband RAs [95,108], [100], one dual band RA at X/K-band [70] and two Ka-band designs [92], [94] while there are two tightly coupled RAs that operate in C-band and Xband, e.g., [107] and [105]. Different lattice periodicity can be observed from Table II such as 𝜆/3, 𝜆/4, 𝜆/5 and 𝜆/6.…”