Mutual Coupling Suppression Between Two Closely Placed Microstrip Patches Using EM-Bandgap Metamaterial Fractal Loading

An approach is proposed to reduce mutual coupling between two closely spaced radiating elements. This is achieved by inserting a fractal isolator between the radiating elements. The fractal isolator is an electromagnetic bandgap structure based on metamaterial. With this technique, the gap between radiators is reduced to <inline-formula> <tex-math notation="LaTeX">$\sim 0.65\lambda $ </tex-math></inline-formula> for the reduction in the mutual coupling of up to 37, 21, 20, and 31 dB in the <inline-formula> <tex-math notation="LaTeX">${X}$ </tex-math></inline-formula>-, <italic>Ku</italic>-, <inline-formula> <tex-math notation="LaTeX">${K}$ </tex-math></inline-formula>-, and <italic>Ka</italic>-bands, respectively. With the proposed technique, the two-element antenna is shown to operate over a wide frequency range, i.e., 8.7–11.7, 11.9–14.6, 15.6–17.1, 22–26, and 29–34.2 GHz. Maximum gain improvement is 71% with no deterioration in the radiation patterns. The antenna’s characteristics were validated through measurement. The proposed technique can be applied retrospectively and is applicable in closely placed patch antennas in arrays found in multiple-input multiple-output and radar systems.