Per-Simon Kildal

Bio: Per-Simon Kildal is an academic researcher from Chalmers University of Technology. The author has contributed to research in topics: Antenna (radio) & Electromagnetic reverberation chamber. The author has an hindex of 60, co-authored 504 publications receiving 13470 citations. Previous affiliations of Per-Simon Kildal include SP Technical Research Institute of Sweden & Norwegian Institute of Technology.

A new approach to the synthesis of reflector antennas

Abstract: This paper presents a new ray method to synthesize shaped offset multireflector antennas which involves solving linear equations. In the other existing techniques, differential equations have to be solved. The advantage of the technique is that the solution is easier to control, so that, for example, low cross-polarization can be obtained and an exact solution can be found. The method is applied to synthesize a dual-reflector feed for the spherical reflector of the radio telescope in Arecibo.

Comparison of blockage widths of ideally hard cylinders of different cross-sectional shapes

Abstract: We have computed the equivalent blockage width of ideally hard cylinders of different cross sections. We have shown that the oblong cross section is best when the physical width is larger than about 0.2square, whereas for narrower cross-sections the transverse thin rectangular cross-section is best. The latter can be strengthened by a star-shaped cross section, without significant change in the blockage width. The latter was found as a result of numerical optimization. The optimized oblong shape is explained by a smooth transition of the waves past the cylinder, which is facilitated by the GO characteristics of the hard surface [8]. The thin rectangular cross section is explained as a quasi-static solution. The cross-section is so narrow in terms of wavelengths that transverse currents cannot be induced. The star-shaped cross-section works like the transverse rectangular cross-section, because the orthogonal rectangular part making up the two other arms of the star are invisible to the wave because of their small thickness. It must be emphasized that we have treated ideally hard cylinders. This makes the results valid for metal cylinders and TE-case. The performance for TM-case depends on the realization of the PMC surface, but the results can be seen as typical performance at the center frequency. The bandwidth will normally be small, but can be up to 20-30% when the artificial magnetic conductor is realized by dielectric coatings.

About Random LOS in Rician Fading Channels for MIMO OTA Tests

Abstract: It is often claimed that Rician fading must also be included for Over-The-Air (OTA) testing of mobile devices with Multiple-input Multiple-output (MIMO) capabilities. However, the Line-Of-Sight (LOS) component varies with orientation and location of the mobile device. Therefore, we study Rician channels with random LOS to determine its significance

Efficient spectral domain Green's function analysis of novel metamaterial bandgap guiding structures

Abstract: The Green's function analysis of oversized waveguides with one wall realized as a periodic structure is presented in this paper. Two different realizations of the periodic structures were considered: the bed-of-nails surface and the mushroom surface. Since the period of these surfaces is small compared to wavelength it is possible to take advantage of the asymptotic boundary conditions in the derivation of the required Green's functions. By doing so, we avoid the usual Floquet mode approach needed in the analysis of periodic surfaces and significantly reduce the overall numerical complexity. The Green's functions developed in this way allow dispersion and electromagnetic field analysis since their poles correspond to surface wave modes and waveguide modes. These results reveal the dispersion characteristics of the observed structures and the bandwidth usable in the waveguide applications. The computed results are compared with the results obtained with a general electromagnetic solver and the agreement is very good.

High-impedance electromagnetic surfaces with a forbidden frequency band

Abstract: 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.

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

Abstract: 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.

Photonic crystals

Abstract: 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.

Transformation optics and metamaterials

Abstract: 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.

The 2017 terahertz science and technology roadmap

Abstract: 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.