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

This paper presents a proposal for a slot array antenna for frequencies above 60 GHz. Also, The array is using the new air gap waveguide as a feeding structure. Here we present a new structure for the parallel plate stop-band based on replacing the uniform cross sectional nails with inverted pyramidal shaped pins. This new type of pin is more suitable for micromachining and manufacturing of gap waveguides above 60 GHz. The wider parallel-plate bandwidth achieved with this new type of pins makes it suitable for integration of very wideband active MMIC circuit with gap waveguide without package resonance problem. Once the RF circuitry is integrated with gap waveguide, the slot arrays can be easily built by having slots on the top metal wall of the gap waveguide thus enabling low cost integrated antenna solution at frequencies above 60GHz.

Increasing parallel plate stop-band in gap waveguides using inverted pyramid-shaped nails for slot array application above 60GHz

Gap waveguides were first presented in [1] as an alternative guiding technology especially attractive for frequencies over 30 GHz up to THz. At those frequencies, the current technologies show some deficiencies regarding to the performance, integration ability, or product cost. Planar technologies, such as microstrip and coplanar, are often chosen due to their good integration ability and manufacture simplicity, but they suffer from higher losses with increasing frequency as well as from the presence of cavity resonances when encapsulated. Hence, hollow waveguides are usually resorted for low-loss applications, in spite of their difficulty for integration with active components and a high manufacturing cost. The need of new transmission line technologies for mm- and sub mm-wave systems is leading to the apparition of alternative technologies. Substrate Integrated Waveguide (SIW) technology has been widely used for high-frequency applications [2], but it exhibits significant losses at increasing frequencies due to wave propagation in substrate. Gap waveguides, on the contrary, support waves in the air gap between two metal plates. One of the plates is provided with a texture, in the form of a bed of nails, to create a high impedance condition at the surface, which in turn forces a cut-off for the parallel-plate modes [3]. On the same plate, there are metal ridges in between the nails providing a path to the waves so that fields are confined to the air gap between the ridges and the metal plate on top. This propagation path can alternatively be provided by a microstrip line lying on the bed of nails, or by a groove in between the nails. An interesting application using similar technology can be found in [4] where a multi-layered phased array antenna developed in Japan was presented.

http://ap-s.ei.tuat.ac.jp/isapx/2012/pdf/2A3-4.pdf

Gap waveguide components for millimetre-wave systems: Couplers, filters, antennas, MMIC packaging

We propose a novel excitation technique of an untilted slot in the narrow wall of a rectangular waveguide. The excitation is realized by inserting into the slot a dielectric plate on which there are etched conducting strips. The strip excitation can control the coupling more easily and accurately than a conventional excitation using tilted wires. We analyze the coupling to the slot by using the dyadic Green's function for the waveguide with the dielectric plate, derived by Seki's (1984) virtual cavity method. A double resonance due to the strip and the slot results in large coupling as well as small variation of the phase of the transmitted wave, both over a wide frequency band. Some results are verified by measurements. The coupling can be tuned by varying the distance between the slot and the strip.

Excitation of an untilted narrow-wall slot in a rectangular waveguide by using etched strips on a dielectric plate

Reflector antennas with self supported waveguide feeds of swan-neck type are often used in radio link systems. If there are requirements for very low sidelobes, it is common to attach an absorbing cylinder to the rim of the reflector. Both the cylinder and the feed are expensive to manufacture. The paper describes a so called hat antenna which is cheap to manufacture, compact, light-weight and in addition has very low sidelobe performance. An experimental model with 43 cm reflector diameter has been built and measured at 15 and 30 GHz.

High performance reflector hat antenna with very low sidelobes for radio-link applications

The paper gives an overview of how measurements in reverberation chambers can be used to characterize the performance of small antennas and wireless terminals for mobile communications in environments with Rayleigh fading. The measurement capabilities include radiation efficiency, radiated power, diversity gain, MIMO system capacity and receiver sensitivity. In the latter case the reverberation chamber enable fast measurements of bit error rate (BER) and frame error rate (FER), and thereby total isotropic sensitivity (TIS). In addition, the terminals can be tested under realistic and continuous fading very similar to what is present in urban and indoor environments, referred to as average fading sensitivity (AFS). The chamber is the only known measurement instrument for directly measuring diversity gain and channel capacity; the alternative being to drive measurement instruments around in an actual urban environment. The measurements can fast and easily be performed for different talk positions relative to a head phantom.

Per-Simon Kildal

Papers

Increasing parallel plate stop-band in gap waveguides using inverted pyramid-shaped nails for slot array application above 60GHz

Gap waveguide components for millimetre-wave systems: Couplers, filters, antennas, MMIC packaging

Excitation of an untilted narrow-wall slot in a rectangular waveguide by using etched strips on a dielectric plate

High performance reflector hat antenna with very low sidelobes for radio-link applications

Overview of 6 Years R&D on Characterizing Wireless Devices in Rayleigh Fading Using Reverberation Chambers