[IEEE 2015 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications (IMWS-AMP) - Suzhou, China (2015.7.1-2015.7.3)] 2015 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications (IMWS-AMP) - Double-layer resistive FSS structure for ultra-wideband microwave absorption