Dielectric lens optimization for conical helix THz antennas

Abstract

In this work the design and characteristics of an extended hemispherical dielectric lens applied to a non-planar antenna for the detection of THz radiation is presented. Antenna and lens behavior is numerically investigated in a large frequency range around the central frequency of 1 THz. Common printable materials widely characterized at THz range are used for the lens realization. Numerical results of the full-wave electromagnetic analysis of some proposed structures are reported and discussed. IntroductionIn last years the interest addressed to the THz region (the frequency range between 0.1 and 10 THz) has grown because of the congestion of the electromagnetic spectrum at lower frequencies and of the need for higher data rate in digital wireless communications [1,2]. Whereas the communication industry is the strongest driver in the exploitation of the THz range, spectroscopy applications [3] and non-destructive testing [4] are today's major applications for THz radiation.The successful utilization of THz technology is subject to the availability of compact, stable, room temperature and low cost sources and detectors. In particular, detectors with high sensitivity are required because of the very high attenuation of THz radiation in the atmosphere and because of the difficulty of producing high-power compact sources.The integrated circuit technology has been identified as the most promising to manufacture reliable and economical detectors for the THz region [5,6]. In particular, in [6] a prototype of 1kpixel THz camera fabricated in commercial 65nm CMOS process has been presented. The camera is feed by USB power, operates at room temperature and has a bandwidth going from 600 GHz to 1 THz. In order to enhance the coupling between its 1024 pixels focal plane array and the outer environment, a silicon lens is places above the camera.Most common materials used for the fabrication of dielectric lenses at THz region are high resistivity silicon and PTFE (Teflon). Usually, a single lens focuses the incident radiation onto a focal plane array. The approach adopting the high resistivity silicon is expensive, thus, low-loss polymers (as PTFE) should be preferred for low cost applications. In a recent work [7], 3D printable and injection moldable materials have been characterized at THz frequencies, as their attractive characteristics in terms of the reduction of lens cost and the possibility to apply wafer level process (3D printing or molding) to produce reproducible arrays of micro-lenses. This configuration contemplates a dielectric micro-lens over every single pixel (detector) constituting the focal plane array [8,9]. Dielectric lenses have been thoroughly studied for millimeter wave and sub-millimeter wave imaging systems to increase the gain of the planar antennas coupled to detectors (slot, bowtie, spiral, log-periodic, etc).

Minimum Lens Size Supporting the Leaky-Wave Nature of Slit Dipole Antenna at Terahertz Frequency

“…The similar trend is seen with greater differences in gain curves for the lens radius of 1.6 . This behavior is attributed to the effect of extension length ( ) which changes the foci of lens position with respect to the antenna [21,22]. This confirms that the antenna gain is sensitive to the lens shape (determined by / ), especially for the larger lenses at high frequencies [12,23].…”