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

We study the probability of detecting the bitstream of a 2 × 1 SIMO polarization-diversity system with co-located orthogonally polarized antenna ports on the receiving side of a free-space propagation environment with arbitrary angle-of-arrival, i.e., in so-called Random-Line-Of-Sight (Random-LOS) propagation environments. We show how the diversity gain degrades in directions where the two orthogonal ports have non-orthogonal far-field functions or an amplitude imbalance. We also show that the system performance is better when one side of the link is circularly polarized and the other side is linearly polarized.

https://publications.lib.chalmers.se/records/fulltext/240830/local_240830.pdf

Investigation of polarization deficiencies in SIMO systems in Random-LOS propagation channels

The paper introduces a new method that can predict the reflection coefficient of a complete large log-periodic array (with large number of elements) by calculating the embedded S-parameters between all input and output ports of similar elements that are embedded in a much smaller log-periodic array. By this method we can apply global optimization scheme such as Genetic Algorithm on embedded element in the smaller log-periodic array to improve the reflection coefficient of the larger log-periodic array very efficiently. As an example, an Eleven feed for 2 – 13 GHz has been optimized by using Genetic Algorithm with the present method. The result is a reflection coefficient below −10 dB from 2 GHz to 13 GHz.

Optimization of large log-periodic dual-dipole antenna by using Genetic Algorithm on embedded element in small log-periodic array

This paper addresses how to define the numerical ports in the gap waveguide microstrip line, and also a study of its characteristic impedance when the parallel-plate stopband is realized by using metal pins. The results presented here are produced using commercially available EM simulators. The paper also includes a study of how to minimize the effect of the transverse locations of the pin structure under the microstrip line, relative to the location of the strip.

Study of the characteristic impedance of gap waveguide microstrip line realized with square metal pins

The paper gives a summary of the work that have been performed in the Antenna group at Chalmers University of Technology on measuring antennas for mobile phones in reverberation chambers. Reverberation chambers were originally developed for EMC measurements. We have shown that it also can be used to measure performance of antennas that are designed for use in multipath propagation environment, as well as the performance of complete phones. The antennas and phones can be measured with or without the presence of a head phantom or other objects. The antenna measurements give both radiation efficiency and reflection coefficient at different positions relative to an object such as a head phantom, as they would appear if the antenna and the head phantom were located in free space. The phone measurements give the total radiated power, which we refer to as the telephone communication power (TCP), also at different positions relative to an object. The present summary includes results from both antenna and phone measurements.

Measurements of mobile phone antennas in small reverberation chambers

The problem of determining the eigenmodes of a rectangular waveguide with one broad hard wall formed by longitudinal corrugations with grooves filled with dielectric is considered. The dispersion equation is derived on the basis of using the asymptotic boundary conditions for corrugated surfaces. It is shown analytically that if the groove depth is equal to the value 0.25λ/(e−1)½ corresponding to the hard wall condition, the TE eigenmode spectrum of the waveguide comprises an infinite set of degenerated quasi-TEM modes with different transverse propagation constants and identical longitudinal propagation constants equal to the wavenumber k. Such solutions are important for understanding the local waves appearing along ridges in such waveguides, that has inspired to the invention of new so-called gap waveguides.

Per-Simon Kildal

Papers

Investigation of polarization deficiencies in SIMO systems in Random-LOS propagation channels

Optimization of large log-periodic dual-dipole antenna by using Genetic Algorithm on embedded element in small log-periodic array

Study of the characteristic impedance of gap waveguide microstrip line realized with square metal pins

Measurements of mobile phone antennas in small reverberation chambers

Analysis of global eigenmodes in an oversized rectangular waveguide with a hard surface on one broad wall for planar slot array antenna applications