Wideband directive emission based on hyperbolic metamaterials Mina Ren, Yanhong Liu, Shengwang Yu, Lijuan Dong, Lixiang Liu, Fusheng Deng and Yunlong Shi Eur. Phys. J. Plus, 134 6 (2019) 301 Published online: 27 June 2019 DOI: 10.1140/epjp/i2019-12745-4