Wideband Integrated Lens Antennas for Terahertz Deep Space Investigation

Abstract

The Terahertz (THz) band is the portion of the spectrum that covers a frequency range from 300 GHz to 3 THz. The potential of this band has been proven for numerous type of applications including medical imaging, non-destructive testing, space observation, spectroscopy and security screening, thanks to its good compromise between the spatial resolution and penetration. Most of these applications demand for high spatial and range resolution of the images, as well as fast acquisition time. To fulll such requirements, focal plane arrays (FPAs) need to comprise a large number of elements and be able to operate over broad bandwidths. Moreover, fabrication of the FPAs with thousands of antenna elements becomes a real issue at such frequencies due to the fabrications constraints and immense manufacturing costs.

This doctoral thesis consists of two parts: Part I focuses on the design of the lens antennas using a multiple feed per lens scenario, specically aiming at imaging for security and the telecommunication systems as potential applications. The aim of the study is to design integrated lens antennas to achieve frequency stable radiation characteristics either to obtain an ecient reflector illumination or to be used directly as an imager over a wideband operation, typically more than one octave. In the literature, double slot antennas have been widely proposed as an ecient lens feeder, yet they are able to operate within a very narrow bandwidth, in the order of 10 - 15%. Due to its wideband characteristics connected array of leaky slot antenna concept has been used as a lens feeder. Depending on the application type, two dierent approaches have been implemented to achieve frequency independent lens radiation: A coherently fed connected leaky slot array based design with a traditional extended hemi-spherical lens for phased array antenna applications and an integrated double shell lens based design where each source element is associated to an independent beam for telecommunication and security systems.

Part II of the thesis focuses on a single feed per lens scenario, specifically aiming at Terahertz (THz) astronomy applications. Such applications mostly require antennas consist of multi-pixels with large operational bandwidths. Many of the sub-mm wave instruments done for this kind of applications are envisioned to have large format focal plane arrays (FPA) that are based on single beam per feed and tight sampling and are coupled to reflector systems with large F/D ratios. Future satellite based, astronomic THz radiometers will be most likely based on cryogenically cooled detectors to reach the highest sensitivities, will consist of tens of thousands receivers to provide a broad eld of view and could address simultaneously a broad portion of the THz band. Several type of reflector feeds have been proposed in the literature including the Vivaldi antennas, horn antennas and the eleven antennas. These antennas, however, are typically optimized to maximize the reflector illumination eciencies as a single reflector feed. As a result, they suer from
the feed taper eciency which is crucial to characterize the total system performance for tightly packed FPAs. No need to mention about the feasibility issues when it comes to the fabrication of the thousands of array elements with the manufacturing techniques available nowadays in sub-mm band. Integrated lens antennas, on the other hand, are widely used in sub-mm band since they allow the integration of the antenna and the detector on the same chip. Space instruments based on cryogenic power detectors often use focal plane arrays based on dielectric lenses. In the literature, the most commonly used lens feed is a double slot antenna, which typically operates in a bandwidth much less than one octave and with single polarization. Sinuous and spiral antennas have been also proposed as wideband lens antenna solutions. However, the fabrication of the feeding lines integrated to the antenna becomes challenging at sub-mm band since they have to be extremely tiny in order not to disturb the radiated elds. To overcome these issues, we propose a highly ecient, dual-polarized wideband leaky lens antenna design that can be integrated to planar feeding lines on the same chip. To our knowledge, the proposed design is the only practical wideband dual polarized antenna solution presently available at sub-mm wave frequencies which lends itself as an extremely useful alternative for next generation sub-mm wave space astronomical instruments.