Erkki Salonen

Bio: Erkki Salonen is an academic researcher from University of Oulu. The author has contributed to research in topics: Antenna (radio) & Dipole antenna. The author has an hindex of 23, co-authored 110 publications receiving 1687 citations. Previous affiliations of Erkki Salonen include Aalto University & Helsinki University of Technology.

Active extragalactic sources - Nearly simultaneous observations from 20 centimeters to 1400 A

Abstract: IRAS, IUE, and ground-based optical, NIR, mm and submm, and radio observations obtained mainly on Apr. 9-23, 1983, are reported for 19 active extragalactic sources and eight control sources. The overall spectra of the compact active sources are shown to be well represented by continuous-curvature functions such as parabolas. The spectra are found to be consistent with models involving continuous particle injection (with synchrotron losses) or first-order Fermi acceleration (with escape and synchrotron losses), but not with models using relativistic Maxwellian electron distributions.

New prediction method of cloud attenuation

Abstract: A new method for cloud attenuation calculation on an earth–satellite link is presented. The method uses temperature and humidity profiles as input parameters. The method has been applied to radiosonde measurements and to the gridded data of the numerical analyses of ECMWF.

Wearable Circularly Polarized Antenna for Personal Satellite Communication and Navigation

Abstract: Integrating antennas into fabrics is a potential way for facilitating many applications, such as health monitoring of patients, fire-fighting, rescue work, and space and military personal communications. This paper studies possibilities to construct a flexible, lightweight and mechanically robust textile antenna for dual-band satellite use: Iridium and GPS. Different textile materials were characterized and the most promising materials were used to design, construct, and test a rectangular patch antenna. The gain and axial ratio for both bands is compliant with specifications and relatively stable under most bending conditions. The developed antenna solution allows integration into clothing.

Improved models for long-term prediction of tropospheric scintillation on slant paths

Abstract: The prediction models for tropospheric scintillation on Earth-satellite paths from Karasawa, Yamada, and Allnutt (1988) and the ITU-R are compared with measurement results from satellite links in Europe, the United States, and Japan at frequencies from 7 to 30 GHz and elevation angles of 3 to 33/spl deg/. The existing prediction models relate the long-term average scintillation intensity to the wet term of refractivity at ground level. The comparison shows that the seasonal variation of scintillation intensity is well predicted by this relation, but for the annual average some additional meteorological information is needed. A much better agreement with measurement results is found when a parameter representing the average water content of heavy clouds is incorporated. This confirms the assumption that scintillation is, at least partly, associated with turbulence inside clouds. The asymmetry between the distributions of signal fade and enhancement can also be explained by turbulence inside clouds. The asymmetry depends on the intensity of the scintillation, which is consistent with the theory assuming a thin layer of cloudy turbulence. A new model based on this theory predicts the distributions of signal fade and enhancement significantly better.

A Frequency Tuning Method for a Planar Inverted-F Antenna

Abstract: A novel method is presented for electrically tuning the frequency of a planar inverted-F antenna (PIFA). A tuning circuit, comprising an RF switch and discrete passive components, has been completely integrated into the antenna element, which is thus free of dc wires. The proposed tuning method has been demonstrated with a dual-band PIFA capable of operating in four frequency bands. The antenna covers the GSM850, GSM900, GSM1800, PCS1900 and UMTS frequency ranges with over 40% total efficiency. The impact of the tuning circuit on the antenna's efficiency and radiation pattern have been experimentally studied through comparison with the performance of a reference antenna not incorporating the tuning circuit. The proposed frequency tuning concept can be extended to more complex PIFA structures as well as other types of antennas to give enhanced electrical performance.

Fiber‐Based Wearable Electronics: A Review of Materials, Fabrication, Devices, and Applications

Abstract: Fiber-based structures are highly desirable for wearable electronics that are expected to be light-weight, long-lasting, flexible, and conformable Many fibrous structures have been manufactured by well-established lost-effective textile processing technologies, normally at ambient conditions The advancement of nanotechnology has made it feasible to build electronic devices directly on the surface or inside of single fibers, which have typical thickness of several to tens microns However, imparting electronic functions to porous, highly deformable and three-dimensional fiber assemblies and maintaining them during wear represent great challenges from both views of fundamental understanding and practical implementation This article attempts to critically review the current state-of-arts with respect to materials, fabrication techniques, and structural design of devices as well as applications of the fiber-based wearable electronic products In addition, this review elaborates the performance requirements of the fiber-based wearable electronic products, especially regarding the correlation among materials, fiber/textile structures and electronic as well as mechanical functionalities of fiber-based electronic devices Finally, discussions will be presented regarding to limitations of current materials, fabrication techniques, devices concerning manufacturability and performance as well as scientific understanding that must be improved prior to their wide adoption

Variability of active galactic nuclei

Abstract: ▪ Abstract A large collective effort to study the variability of active galactic nuclei (AGN) over the past decade has led to a number of fundamental results on radio-quiet AGN and blazars. In radio-quiet AGN, the ultraviolet (UV) bump in low-luminosity objects is thermal emission from a dense medium, very probably an accretion disk, irradiated by the variable X-ray source. The validity of this model for high-luminosity radio-quiet AGN is unclear because the relevant UV and X-ray observations are lacking. The broad-line gas kinematics appears to be dominated by virialized motions in the gravity field of a black hole, whose mass can be derived from the observed motions. The “accretion disk plus wind” model explains most of the variability (and other) data and appears to be the most appropriate model at present. Future investigations are outlined. In blazars, rapid variability at the highest energies (gamma-rays) implies that the whole continuum is relativistically boosted along the line of sight. The gener...

Satellite communications at KU, KA, and V bands: Propagation impairments and mitigation techniques

Abstract: This article surveys the alternative fade mitigation techniques for satellite communication systems operating at Ku, Ka and V frequency bands. The specific phenomena influencing the propagation of radiowaves on Earth-space links are also overviewed. Emphasis is placed on modeling, experimental work carried out in the past, and practical implementations related to each mitigation technique.

Log-parabolic spectra and particle acceleration in the BL Lac object Mkn 421: Spectral analysis of the complete BeppoSAX wide band X-ray data set

Abstract: We report the results of a new analysis of 13 wide band BeppoSAX observations of the BL Lac object Mkn 421. The data from LECS, MECS and PDS, covering an energy interval from 0.1 to over 100 keV, have been used to study the spectral variability of this source. We show that the energy distributions in different luminosity states can be fitted very well by a log-parabolic law F(E) = K (E/E1) −(a+b Log(E/E1)) , which provides good estimates of the energy and flux of the synchrotron peak in the SED. In the first four short observations of 1997 Mkn 421 was characterized by a very stable spectral shape, with average values a = 2.25 and b = 0.45, independently of the source brightness and of the fact that the source luminosity was increasing or decreasing. In the observations of 1998 smaller values for both parameters, a � 2.07 and b � 0.34, were found and the peak energy in the SED was in the range 0.5-0.8 keV. The observations of May 1999 and April-May 2000 covered runs of a duration of several days and provided a very high number of events for all the instruments. The resulting spectral fits were then limited by some instrumental systematics. Also in these cases, the log-parabolic model gave a satisfactory description of the overall SED of Mkn 421. In particular, in the observations of spring 2000 the source was brighter than the other observations and showed a large change of the spectral curvature. Spectral parameters estimates gave a � 1. 8a ndb � 0.19 and the energy of the maximum in the SED moved to the range 1-5.5 keV. We give a possible interpretation of the log-parabolic spectral model in terms of particle acceleration mechanisms. An energy distribution of emitting particles with curvature close to the one observed can be explained by a simple model for statistical acceleration with the assumption that the probability for a particle to increase its energy is a decreasing function of the energy itself. A consequence of this mechanism is the existence of a linear relation between the spectral parameters a and b ,w ell confirmed by the estimated values of these two parameters for Mkn 421.

Spherical near-field antenna measurements

Abstract: From the material presented here, it is clear that the theory underlying the SNF approach is complex and involved to implement. However, it is also very elegant and provides one with many measurement options and powerful capabilities. The numerical implementation of the theory can be efficiently deployed through the use of the fast Fourier transform (FFT) enabling transforms of even electrically large antennas to be accomplished in a matter of a few seconds on a modern powerful digital computer. With the advent of commercially available SNF test systems, the user can exploit these techniques, largely unimpeded by the burden of the theory or the implementation thereof. The material presented here highlighted some of the fundamental concepts and limitations the user needs to be aware of in order to use these test systems with confidence.