Broadband gain enhancement of an UWB antenna using conformal wideband NRI metamaterial

摘要

In this article, broadband gain enhancement of an ultra-wide band (UWB) antenna is achieved by using 4 x 4 array of a wideband negative refractive index (NRI) metamaterial as a reflector layer. A novel shaped metamaterial sized 14.8 x 14.8 mm(2) with double negative (DNG) characteristics in three frequency regions has been fabricated on a flexible FR4 with 0.25 mm thickness. The proposed meta-material gives a continuous NRI bandwidth of 10 GHz (2-12 GHz). The effective parameters of the unit cell cover S, C, X, and Ku-band independently and show DNG region of 6.1 GHz at C (4-8 GHz) and X band (8.8-10.5 GHz, 11.2-11.6 GHz). The unit cell structure is also found to be feed insensitive. The unit cell has small volume of 54.76 mm(3) along with flexible nature which makes it suitable for wearable applications. For a 4 x 4 array the metamaterial still exhibits DNG characteristics. To understand the physical behavior of the unit cell, the circuit analysis along with the study of magnetic and electric field distribution at three resonance frequencies (2.2, 8.2 and 14.2 GHz) is done. Both simulation and measured results indicate that the gain and bandwidth of metamaterial antenna are enhanced by 2 dB and 0.8 GHz.