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 characterization of the performance of wireless devices is key to developing new RF products conforming to the latest communications protocols. Traditionally, communication performance tests have focused on the RF performance of the tested devices, e.g., smart phones, pads, laptops, and so on. In particular, the focus has shifted from conducted (i.e., cabled) measurements to more realistic over-the-air (OTA) characterization of the RF performance of these devices in transmit or receive mode. For example, the receiver performance of 2G and 3G wireless devices can be measured in terms of the total isotropic sensitivity (TIS) that depends on the antenna and the receiver parts of a wireless device. These measurements can be performed in a reverberation chamber setup. However, standard TIS measurements can be time-consuming and do not reflect the actual performance gains of multiple-input multiple-output antenna systems operating over orthogonal frequency division multiplexing channels, such as those encountered in 4G long-term evolution (LTE) systems. Therefore, in order to meet both time and cost efficiency requirements, we propose here a new method to determine the TIS, as well as the diversity performance, of an LTE device based on throughput measurements. The proposed method shows that the TIS of an LTE device is characterized much faster directly from OTA throughput measurements than from standard TIS measurements and with excellent accuracy.

Interpreting the Total Isotropic Sensitivity and Diversity Gain of LTE-Enabled Wireless Devices From Over-the-Air Throughput Measurements in Reverberation Chambers

Traditionally, the reverberation chamber has been used as a low-loss cavity to gain high signal levels. For testing of the radiated properties of wireless terminals and their antennas, this is not an issue, and lossy objects like for instance a head phantom can be introduced in the chamber without problem. However, for testing of active units, the bandwidth of the system itself plays an important role. In order to avoid distortion of the signal transmitted in the chamber, the bandwidth of the chamber must be larger than the bandwidth of the signal. This is one reason for loading the reverberation chamber. Another reason is a potential increase in the measurement accuracy, since an increased bandwidth makes more modes excited at a particular frequency. The purpose of this paper is to investigate the effect of loading on the statistics of the chamber and its bandwidth

Investigation of Heavily Loaded Reverberation Chamber for Testing of Wideband Wireless Units

We propose that the rich isotropic multipath environment should be a reference environment for OTA (over-the-air) characterization of wireless stations for use in multipath, in the same way as the anechoic environment is a reference environment for antennas mounted on masts and rooftops. The rich isotropic multipath environment is emulated by a well designed reverberation chamber, but also by a spherical array of probes in an anechoic chamber. The present paper describes a ray-based simulation tool, ViRM-Lab, which enables users to study the performance of arbitrary user-defined multiport antenna located in user-specified multipath environment. The antennas are defined by their far-field functions of the embedded element (with the other ports matched-load terminated). The environment can be determined by its Angle-of-Arrival (AoA) distribution, richness, and polarization balance. The code is made in such a way that the convergence of the cumulative distribution function (CDF) received on all ports can be studied, as well as the convergence of the statistical expectations when estimating the ergodic Shannon capacity and diversity gain.

Ray based multipath simulation tool for studying convergence and estimating ergodic capacity and diversity gain for antennas with given far-field functions

A method of improving the radiation characteristics of a dipole-disk antenna by using a beam-forming ring (BFR) is suggested. The radiation patterns of the dipole-disk antenna are calculated by the moment methods (MM) and the uniform geometrical theory of diffraction (UTD) and are compared with experimental results.

Dipole-disk antenna with beam-forming ring

An asymptotic theory is presented with which the reduction in aperture efficiency caused by diffraction from a subreflector edge can be calculated for any dual-reflector system. The theory is applied to conventional Cassegrain antennas, for which approximate analytical effieiency formulas are derived. These formulas show that subreflector diffraction may represent a significant efficiency loss even for subreflector diameters as large as 20 wavelengths. The formulas are used to obtain an optimum subreflector size which represents the best trade-off between losses due to subreflector diffraction and geometrical shadowing.

Per-Simon Kildal

Papers

Interpreting the Total Isotropic Sensitivity and Diversity Gain of LTE-Enabled Wireless Devices From Over-the-Air Throughput Measurements in Reverberation Chambers

Investigation of Heavily Loaded Reverberation Chamber for Testing of Wideband Wireless Units

Ray based multipath simulation tool for studying convergence and estimating ergodic capacity and diversity gain for antennas with given far-field functions

Dipole-disk antenna with beam-forming ring

The effects of subreflector diffraction on the aperture efficiency of a conventional Cassegrain antenna--An analytical approach