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. 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 lambda/2 apart . If a separator such as a standard metal sheet is placed in between two antennas to reduce coupling, each must be at least lambda/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 lambda/4) when placed over a magnetically conducting surface. 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 HFSStrade.