Composite planar double-sided AMC surfaces for MIMO applications

Increasing consumer demand for additional and more capable wireless and high-speed data services has led to many new wideband and multiband communications devices. Multiple-input multiple-output (MIMO) antenna systems are one such technology that can increase data rates, provide robustness and reduce interference [1]. However, mutual coupling issues can arise from having multiple antennas in compact and mobile MIMO devices. For reduced mutual coupling, antennas are typically spaced at a minimum of λ/2 apart [2]. If a separator such as a standard metal sheet is placed in between two antennas to reduce coupling, each must be at least λ/4 away from the screen for proper operation. However, from image theory it is known that antennas can efficiently work in close proximity (less than λ/4) when placed over a magnetically conducting surface [2]. A new design technique is introduced here for creating thin, double-sided artificial magnetic conductor screens for isolation of two closely placed antennas. Doubly periodic thin surfaces with electrically small unit cells are designed and optimized using a genetic algorithm (GA). A practical example using closely spaced monopole antennas is created and verified using Ansoft HFSS™.