Reduction of Mutual Coupling in K-Band Microstrip Antennas: A Study on 4×4 Arrays with Defected Ground Structures

This paper presents a 4×4 microstrip array antenna (MAA) based on the optimal spacing of the array elements at 24 GHz with defected ground structure (DGS). At first, a 2×2 array antenna is designed and optimized in terms of inter-element spacing considering the gain, radiation efficiency, mutual coupling (MC), and the side lobe level (SLL). To reduce MC, the DGS is introduced at the ground plane of the 4×4 array by creating three horizontal and three vertical lines, helping to mitigate the flow of surface waves between adjacent and diagonal elements. Due to the DGS structure, the MC between the adjacent elements is reduced by a range of 3–13 dB, while between the diagonal elements, MCs are reduced by 8–13 dB compared to the array without DGS. The gain of the single element, 2×2 and 4×4 array are 7.14 dB, 12.6 dBi, and 18.4 dBi, respectively. The minimum return loss of both the arrays (2×2 and 4×4) is −28 dB with 95% radiation efficiency which ensures excellent impedance matching property.