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Bing Zhang [1] and Wei Chen [2] and Yanjie Wu [3] and Kang Ding [4] and Rongqiang Li [5]

Academic Editor: Xiulong Bao

1, College of Electronics and Information Engineering, Sichuan University, Chengdu 610064, China, scu.edu.cn

2, Department of Electrical and Computer Engineering, Faculty of Engineering, National University of Singapore, Singapore, 117583, nus.edu.sg

3, School of Physics and Optoelectronic Engineering, Guangdong University of Technology, Guangzhou 510006, China, gdut.edu.cn

4, National Key Laboratory on Electromagnetic Environmental Effects and Electro-Optical Engineering, PLA University of Science and Technology, Nanjing 210007, China, ust.com.cn

5, School of Electronic Engineering, Chengdu University of Information Technology, Chengdu 610225, China, cuit.edu.cn

Received Mar 23, 2017; Revised Jun 10, 2017; Accepted Jun 19, 2017

This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

1. Introduction

Terahertz (THz) waves, or submillimeter/far-infrared waves, are defined as the electromagnetic (EM) radiation in the frequency from 0.1 to 10 THz. They cover a large portion of the EM spectrum between mid-infrared and microwave bands. This spectral domain has low frequency crystalline lattice vibrations and other intermolecular vibrations in many chemical and biological materials, including explosives, drugs, and other biomolecules. Many polar gases also have the distinctive finger print in the THz spectrum. The absorbed and reflected THz waves of these materials contain information that is not available in other frequency ranges. Hence, the THz is extensively explored for sensing and imaging applications. As a potential modality for sensing and imaging, the THz is considered safe because of its penetration capability through obstacles like paper, textile, ceramic, wood, and leather with negligible attenuation. THz technologies are also used for noninvasive and nondestructive sensing of targets under covers. Recently, THz spectroscopy and imaging of explosive related component have been investigated for defense usage.

Compared with relatively well-developed technologies and widespread applications in microwave, mid-infrared and optical bands, research, design, and technology developments in the THz band are still in infancy. A THz system is built up of various active and passive components. For the antenna and other passive devices, their dimensions are usually proportional to the wavelength. The wavelength of the THz EM waves lies in the range of 3 mm–30 

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