A new type of metallic electromagnetic structure has been developed that is characterized by having high surface impedance. Although it is made of continuous metal, and conducts dc currents, it does not conduct ac currents within a forbidden frequency band. Unlike normal conductors, this new surface does not support propagating surface waves, and its image currents are not phase reversed. The geometry is analogous to a corrugated metal surface in which the corrugations have been folded up into lumped-circuit elements, and distributed in a two-dimensional lattice. The surface can be described using solid-state band theory concepts, even though the periodicity is much less than the free-space wavelength. This unique material is applicable to a variety of electromagnetic problems, including new kinds of low-profile antennas.

/pdf/high-impedance-electromagnetic-surfaces-with-a-forbidden-3vtu72a5an.pdf

High-impedance electromagnetic surfaces with a forbidden frequency band

Herschel was launched on 14 May 2009, and is now an operational ESA space observatory o ering unprecedented observational capabilities in the far-infrared and submillimetre spectral range 55 671 m. Herschel carries a 3.5 metre diameter passively cooled Cassegrain telescope, which is the largest of its kind and utilises a novel silicon carbide technology. The science payload comprises three instruments: two direct detection cameras/medium resolution spectrometers, PACS and SPIRE, and a very high-resolution heterodyne spectrometer, HIFI, whose focal plane units are housed inside a superfluid helium cryostat. Herschel is an observatory facility operated in partnership among ESA, the instrument consortia, and NASA. The mission lifetime is determined by the cryostat hold time. Nominally approximately 20,000 hours will be available for astronomy, 32% is guaranteed time and the remainder is open to the worldwide general astronomical community through a standard competitive proposal procedure.

/pdf/herschel-space-observatory-an-esa-facility-for-far-infrared-3pdcouv7zo.pdf

Herschel Space Observatory - An ESA facility for far-infrared and submillimetre astronomy

The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

Transformation optics describes the capability to design the path of light waves almost at will through the use of metamaterials that control effective materials properties on a subwavelength scale. In this review, the physics and applications of transformation optics are discussed.

Transformation optics and metamaterials

Science and technologies based on terahertz frequency electromagnetic radiation (100 GHz–30 THz) have developed rapidly over the last 30 years. For most of the 20th Century, terahertz radiation, then referred to as sub-millimeter wave or far-infrared radiation, was mainly utilized by astronomers and some spectroscopists. Following the development of laser based terahertz time-domain spectroscopy in the 1980s and 1990s the field of THz science and technology expanded rapidly, to the extent that it now touches many areas from fundamental science to 'real world' applications. For example THz radiation is being used to optimize materials for new solar cells, and may also be a key technology for the next generation of airport security scanners. While the field was emerging it was possible to keep track of all new developments, however now the field has grown so much that it is increasingly difficult to follow the diverse range of new discoveries and applications that are appearing. At this point in time, when the field of THz science and technology is moving from an emerging to a more established and interdisciplinary field, it is apt to present a roadmap to help identify the breadth and future directions of the field. The aim of this roadmap is to present a snapshot of the present state of THz science and technology in 2017, and provide an opinion on the challenges and opportunities that the future holds. To be able to achieve this aim, we have invited a group of international experts to write 18 sections that cover most of the key areas of THz science and technology. We hope that The 2017 Roadmap on THz science and technology will prove to be a useful resource by providing a wide ranging introduction to the capabilities of THz radiation for those outside or just entering the field as well as providing perspective and breadth for those who are well established. We also feel that this review should serve as a useful guide for government and funding agencies.

https://iopscience.iop.org/article/10.1088/1361-6463/50/4/043001/pdf

The 2017 terahertz science and technology roadmap

The design of the cryogenic 2-14 GHz Eleven feed for reflector antennas in future wideband radio telescope involves electrical design of the Eleven antenna, design of center puck, different alternative solutions for integrating with low noise amplifiers (LNAs), mechanical and cryogenic design and tests, system noise temperature estimation and so on. All these design aspects will be described in the paper. A large quantity of simulated and measured data has been obtained in order to verify the electrical, mechanical and cryogenic performance, and the system noise temperature. The objective of this work is to provide a good feed candidate for reflector antennas in VILB 2010 and US SKA projects. The system configuration of the Eleven feed can be represented by the block diagram shown in Fig. 1, which consists of three parts: the Eleven antenna, center puck and the LNA-integration circuit board. Fig. 2 shows a photo of the Eleven feed. The reflection coefficient measured at Caltech (California Institute of Technology) is shown in Fig. 3, and the aperture efficiency and other subefficiencies measured at DTU (Denmark University of Technology) are shown in Fig. 4. Fig. 5 shows Steady state analysis of the thermal distribution along the feed with head load of 20W/m2. More simulated and measured data will be shown in the paper. In conclusion, the Eleven feed has good performance in the frequency range of 2 – 14 GHz, and has gone through several cryogenic tests.

Design of cryogenic 2-14 GHz eleven feed for reflector antennas for future radio telescopes

System noise calculations over the decade bandwidth of the Eleven feed

The next generation VLBI systems require the design of a wideband receiver covering the 2-14 GHz range, necessitating a wideband feed. Presented here are the 2009 development of a cryogenic 2-14 GHz Eleven feed for reflector radio telescope antennas, including its integration into a cryogenic receiver. The Eleven feed is designed for dual linear polarization and consists of four log-periodic folded dipole arrays. Each pair of arrays is fed by a differential two-wire transmission line connected either to balun or a differential LNA. The present configuration has been measured in many configurations, at various independent labs - corresponding simulations have been done. The results show (across the band) a high polarization efficiency for the feed, with a nearly constant beam width, a reflection coefficient below -10dB, and a constant phase center. Electrical parameters under cryogenic conditions and measured receiver noise temperatures are presented.

/pdf/cryogenic-integration-of-the-2-14-ghz-eleven-feed-in-a-47vm1qm9nz.pdf

Per-Simon Kildal

Papers

Design of cryogenic 2-14 GHz eleven feed for reflector antennas for future radio telescopes

System noise calculations over the decade bandwidth of the Eleven feed

Cryogenic Integration of the 2-14 GHz Eleven Feed in a Wideband Receiver for VLBI2010

Analysis of a circular hard strip-loaded horn by using the method of generalized scattering matrices

Design of a dual-polarized horn antenna with very high aperture efficiency by using PBG hard surface walls