Erkki Salonen

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

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.

Wearable Circularly Polarized Antenna for Personal Satellite Communication and Navigation

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.

A Frequency Tuning Method for a Planar Inverted-F Antenna

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 antennas 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.

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

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.

Multifrequency observations of blazars. III - The spectral shape of the radio to X-ray continuum

Multifrequency, quasi-simultaneous spectra for a sample of 11 blazars are presented. The spectral shape of the violently variable millimeter to ultraviolet flux is consistent with emission from a very compact single component which becomes self-absorbed at wavelengths longer than about 3 mm. The centimeter emission can be attributed to a separate, more slowly varying component. Three out of four optically violent variable quasars also exhibit evidence of a UV excess component. Values for the size of the flaring regions of 0.001-0.1 pc and magnetic fields of order 1 G are deduced. It is found that photon energy densities may dominate over magnetic field energy densities, in which case inverse Compton scattering may be the dominant energy loss mechanism in flaring components.

Predictions of radiowave attenuations due to a melting layer of precipitation

A melting layer model related to the physical constants and meteorological parameters is employed in this investigation. The specific phase shift, together with the specific attenuation, is computed at 1-100 GHz by using the Mie theory. The additional zenith attenuation, which is the difference between zenith attenuation due to the melting layer and attenuation due to the same thickness of the resulting rain, is comprehensively studied. The ratio of the difference to rain zenith attenuation may be over 1 at 1-5 GHz although the difference is much less than 1 dB. The difference can be over 1 dB at frequencies above 20 GHz. A minimum of the ratio is below 0.05 at frequencies about 40-60 GHz but the ratio can become a value of about 0.1 at 100 GHz. The additional attenuation should be taken into account in satellite-Earth communications and radar remote sensing. The power law parameters of the average specific attenuation of the melting layer and rain specific attenuation are tabulated for three raindrop size distributions at rain rates of below 25 mm/h. The power law method could be utilized in the additional attenuation calculation. It is a good approximation of the Mie theory results at 1-50 GHz and a useful estimate at 50-100 GHz. >

Prediction model for the diurnal behavior of the tropospheric scintillation variance

Tropospheric scintillation is caused by variations of the refractive index due to turbulence. The only meteorological input parameter for two common current scintillation models by Karasawa et al. (1988) and by the ITU-R is the monthly average of the wet part of the refractivity N/sub wet/ at ground level, which is not directly associated with turbulence. The diurnal correlation between N/sub wet/ and scintillation variance is very weak. Because clouds and cloud formation are closely associated with the turbulence, quantitative cloud parameters were looked for. Cloud type information based on edited synoptic cloud reports are available from the common database of CDIAC and NCAR. Both diurnal and seasonal variations between scintillation variance and average amount of Cumulus type clouds are well correlated. Using this cloud information together with N/sub wet/, a new method for tropospheric scintillation variance predicting also the diurnal variations is introduced. This model is derived and tested using scintillation measurements at four sites in different climates in Finland, United Kingdom, Japan, and Texas.

CAPACITIVE RECOGNITION OF THE USER'S HAND GRIP POSITION IN MOBILE HANDSETS

A capacitive method for measuring hand grip position on a mobile phone equipped with a dual-band planar inverted-F antenna (PIFA) and a monopole antenna was studied using difierent electrode arrangements. A capacitive sensor with a dual-electrode conflguration and an antenna-integrated capacitive sensor for hand grip recognition were developed. The sensitivities of the sensors were measured along the front, side and back of the phone. The dual-electrode sensor conflguration exhibited its best sensitivity of 29fF at the bottom end of the phone. The PIFA antenna-integrated sensor proved to have sensitivity of 420fF and the monopole antenna-integrated sensor had sensitivity of 115fF, making them both reasonable solutions for hand grip sensors in mobile applications.

Low Mutual Coupling Between Monopole Antennas by Using Two

A simple structure for achieving low mutual coupling between two monopole antennas at 2.45 GHz center frequency is studied. The structure has two half-wavelength slots cut into the ground plane between the monopoles. The lowest mutual coupling is between -54 and -35 dB, depending on the studied structure. In comparison, mutual coupling using the reference ground planes is between -15 and 7 dB. The improvement in measured total efficiencies with the slotted ground plane against the reference ground planes is between 2.8 and 24.3%.

\lambda/2

This letter presents a planar wideband polarization diversity antenna for mobile terminals. The antenna consists of two orthogonally oriented quasi-complementary antennas (QCA) formed by the combination of an electric dipole and a magnetic slot and located at the separate ends of a mobile ground plane. The studies with a single quasi-complementary antenna element show that the electric dipole and the magnetic slot are partly compensating each other providing large bandwidth and offering good radiation properties. The measured -6-dB impedance bandwidth of the individual QCA is from 1.8 to 4.6 GHz, corresponding to an 87.5% relative bandwidth. The measured S21 is less than - 18 dB within the - 6-dB impedance bandwidth. The average measured total efficiency at the aforementioned bandwidth is - 0.95 dB. The measured radiation patterns are presented at 2 and 4 GHz with orthogonal polarizations. Finally, the measured envelope correlation and effective diversity gain (EDG) as a function of frequency are presented, with a maximum correlation less than 0.01 and EDG better than 8.0 dB.