Terahertz antenna technology for imaging applications: a technical review

The terahertz (THz) regime of the electromagnetic spectrum is rich with the emerging possibilities in imaging applications with unique characteristics to screening for weapons, explosives and bio-hazards, imaging of concealed objects, water content, and skin, and these advantages can be harnessed by using the effective THz sources and detectors. In THz imaging systems, the pulsed THz sources and detectors find unique applications and thus we have emphasized on re-visiting these kinds of systems. Several novel imaging techniques which exploit the distinctive properties of the THz systems have been presented. Moreover, the THz antenna is one of the most important components of a THz imaging system as it plays a significant role in both impedance matching and power source. Therefore, the recent developments in THz antenna design for imaging applications are reviewed and the potential challenges of such THz systems are investigated. The photoconductive antennas form the basis of many THz imaging and spectroscopy systems and finds promising applications in various scientific fields. However, for the imaging applications, there is a requirement of planar and compact THz antenna sources with on-chip fabrication and high directivity in order to achieve large depth-of-field for better image resolution. Therefore, the key modalities of improving photoconductive dipole antennas performance are identified for imaging applications. Also, the ways to improve the directivity of the photoconductive dipole antenna are discussed. The main purpose of this review is to provide an assortment of all relevant literature to bring researchers up-to-date on the current state-of-the-art and potential challenges of THz antenna technology for imaging applications.