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

Design of hat fed reflector antennas using FDTD

Handheld terminals such as mobile phones incorporate more and more multimedia functionality. This is a challenge for the terminal designers, since higher download speed is demanded. Therefore, a lot of research effort is currently spent on approaches to enhance download speed. One approach is to use multiple antennas on both the transmitting and receiving sides. If there are M antenna ports on the transmit side and N on the receive side, there will be MxN signal channels through the multipath environment, thereby allowing for higher data speed than if only one single channel is used. This is commonly referred as a MIMO-system. Multipath environments can be emulated in a reverberation chamber and hence the performance of a MIMO system can be measured there [1]. It is not obvious how to design good antennas for MIMO systems, since classical array theory can not be used. The maximum available capacity of the MIMO antenna system in an isotropic Rayleigh environment can in principle be calculated and used as a cost function in the optimization process of the antenna. However, most antenna engineers do not have any feeling for how to optimize the MIMO capacity and can not give a good starting point for the optimization process. Hence, it will be useful to find how classical antenna performance parameters like radiation efficiency and mutual coupling affect the MIMO-capacity, as shown initially in [2] by characterization both in reverberation chamber and by simulation. The correlation between the antenna ports in the multipath environment also affect the performance but was shown to be a minor effect compared to the radiation efficiency. The reverberation chamber has also been used to characterize the MIMO antennas in [3] and [4]. The purpose of the present paper is to compare the performance of three different practical linear MIMO arrays, each with 4 radiating elements, but having different element spacing. Previously, a circular array of monopoles was studied for different element spacing in [2].

http://ap-s.ei.tuat.ac.jp/isapx/2008/pdf/1645158.pdf

Degradation of MIMO-capacity due to correlation and efficiency of practical antennas

Characterization of mobile phones on reception by measurements of total isotropic sensitivity and average fading sensitivity in reverberation chamber

Analysis of SW excitation and radiation mechanisms of a monopole antenna on a circular grounded dielectric slab with critical thickness

A rotationally symmetric cellular phone with a monopole antenna is comprehensively analysed. The radiation efficiency is studied as a function of the size of the phone body and of the antenna length. Further, the possibility of shortening the monopole by coating it with a highpermittivity dielectric at the monopole is investigated. All calculations are performed both with and without a model of a human hand holding the phone. The Method of Moments is used for the simulations and the results are confirmed by measurements. A very good agreement is observed.

Per-Simon Kildal

Papers

Design of hat fed reflector antennas using FDTD

Degradation of MIMO-capacity due to correlation and efficiency of practical antennas

Characterization of mobile phones on reception by measurements of total isotropic sensitivity and average fading sensitivity in reverberation chamber

Analysis of SW excitation and radiation mechanisms of a monopole antenna on a circular grounded dielectric slab with critical thickness

Analysis of a rotationally symmetric cellular phone with a monopole antenna