| 1. |
- Alayon Glazunov, Andres
(författare)
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A survey of the application of the spherical vector wave mode expansion approach to antenna-channel interaction modeling
- 2014
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Ingår i: Radio Science. - 0048-6604 .- 1944-799X. ; 49:8, s. 663-679
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Tidskriftsartikel (refereegranskat)abstract
- This paper provides an overview of recent advances in the modeling, analysis, and measurements of interactions between antennas and the propagation channel in multiple antenna systems based on the spherical vector wave mode expansion of the electromagnetic field and the antenna scattering matrix. It demonstrates the importance and usefulness of this approach to gain further insights into a variety of topics such as physics-based propagation channel modeling, mean effective gain, channel correlation, propagation channel measurements, antenna measurements and testing, the number of degrees of freedom of the radio propagation channel, channel throughput, and diversity systems. The paper puts particular emphasis on the unified approach to antenna-channel analysis at the same time as the antenna and the channel influence are separated. Finally, the paper provides the first bibliography on the application of the spherical vector wave mode expansion of the electromagnetic field to antenna-channel interactions.
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| 2. |
- Beghin, Christian, et al.
(författare)
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Modeling of CLUSTER's electric antennas in space : application to plasma diagnostics
- 2005
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Ingår i: Radio Science. - 0048-6604 .- 1944-799X. ; 40:6, s. RS6008-
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Tidskriftsartikel (refereegranskat)abstract
- [1] The main characteristics of the long-boom electric antennas installed on board the Cluster satellites are derived from finite element modeling in a kinetic and isotropic space plasma, in the frequency range of about 1–100 kHz. The model is based on the surface charge distribution method in quasi-static conditions. The impedances of both types of antenna, i.e., the double-wire and the double-probe, are computed versus the frequency normalized with respect to the local plasma frequency and for several different Debye lengths. Most of the code outputs are checked using analytic estimations for better understanding of the involved physical mechanisms. As a by-product, the effective length of the double-probe antenna and the mutual impedance between the two antennas are computed by the code. It is shown that if it had been possible to implement such measurements on board, one would have been able not only to determine accurately the electric characteristics of the antennas but also to estimate the local plasma parameters. Nevertheless, an interesting feature predicted by the model has been checked recently in orbit by running a special mode of operation for testing the mutual impedance measurement. The preliminary results are globally consistent with the predictions, except that they suggest that our Maxwellian model for the electron distribution should be revised in order to explain the unexpected low-frequency response. After analysis of the electron flux measurements obtained simultaneously, it appears that a rough adjustment of the electron distribution with a two-component distribution allows us to account for the observations.
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| 3. |
- Buehler, Stefan, et al.
(författare)
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Expected performance of the superconducting submillimeter-wave limb emission sounder compared with aircraft data
- 2005
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Ingår i: Radio Science. - 0048-6604 .- 1944-799X. ; 40:3
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Tidskriftsartikel (refereegranskat)abstract
- The simulated retrieval performance of a submillimeter wave limb sounder was compared with that of an up-looking instrument with identical observation frequency bands and comparable noise temperature. The frequency bands were 624.32-626.32 and 649.12-650.32 GHz, and the retrieval simulations focused on the key trace gas species O-3, HCl, and ClO. As expected, the limb geometry leads to a better altitude resolution and larger measurement altitude range. The same retrieval setup was applied to measured spectra, taken by the up-looking Airborne Submillimeter Radiometer ( ASUR) instrument on 4 September 2002 at 19.11 degrees E, 71.90 degrees N and on 19 September 2002 at 44.10 degrees E, 4.10 degrees S. The observed structures in the fit residual near the HCl spectral lines at 625.9 GHz lead to the conclusion that the pressure shift parameter of HCl is likely to be higher than the value in the HITRAN spectroscopic database. Depending on the assumed temperature dependence of the shift, the HCl pressure shift value consistent with the ASUR data is 0.090-0.117 MHz/hPa instead of the 0.030 MHz/hPa reported in HITRAN. This result is in good agreement with very recent independent laboratory work which suggests a value of 0.110 MHz/hPa for the shift.
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| 4. |
- Davis, J.L, et al.
(författare)
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Geodesy by radio interferometry: Effects of atmospheric modeling errors on estimates of baseline length
- 1985
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Ingår i: Radio Science. - 0048-6604 .- 1944-799X. ; 20:6, s. 1593-1607
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Tidskriftsartikel (refereegranskat)abstract
- Analysis of very long baseline interferometry data indicates that systematic errors in prior estimatesof baseline length, of order 5 cm for ~8000-km baselines, were due primarily to mismodeling of theelectrical path length of the troposphere and mesosphere ("atmospheric delay"). Here we discussobservational evidence for the existence of such errors in the previously used models for the atmosphericdelay and develop a new "mapping" function for the elevation angle dependence of this delay. Thedelay predicted by this new mapping function differs from ray trace results by less than ~5 mm, at allelevations down to 5° elevation, and introduces errors into the estimates of baseline length of •
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| 5. |
- Davis, J.L., et al.
(författare)
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Ground-based measurement of gradients in the “wet” radio refractivity of air
- 1993
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Ingår i: Radio Science. - 0048-6604 .- 1944-799X. ; 28:6, s. 1003-1018
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Tidskriftsartikel (refereegranskat)abstract
- We have used a ground-based microwave radiometer, known as a water vapor radiometer, to investigate the local spatial and temporal variation of the wet propagation delay for a site on the west coast of Sweden. The data were obtained from a wide range of azimuths and from elevation angles greater than 23.6-degrees (air mass 2.5). Visual inspection of the data suggested a simple ‘'cosine azimuth” variation, implying that a first-order gradient model was required. This model was adequate for short time spans up to approximately 15 min, but significant temporal variations in the gradient suggested to us that we include gradient rate terms. The resulting six-parameter model has proven adequate (rms delay residual approximately 1 mm) for up to 30 min of data. Assuming a simple exponential profile for the wet refractivity gradient, the estimated gradient parameters imply average surface wet-refractivity horizontal gradients of order of 0.1-1 N km-1. These gradients are larger, by 1-2 orders of magnitude, than gradients determined by others by averaging over long (approximately 100-km) distances. This result implies that for applications that are sensitive to local gradients, such as wet propagation-delay models for radio-interferometric geodetic studies, the use of meteorological data from widely spread stations may be inadequate. The gradient model presented here is inadequate for times longer than about 30 min. even if no gradients are present, because of the complicated stochastic like temporal behavior of the wet atmosphere. When gradients are present, they can change magnitude by approximately 50% over 10-15 min. Nevertheless, our ability to fit the radiometer data implies that on timescales 23.6-degrees, the local structure of the wet atmosphere can be described with a simple model. (The model is not limited to this range of elevation angles in principle.) The estimated gradient and gradient rate vectors have preferred directions, which indicates a prevailing structure in the three-dimensional temperature and humidity fields, possibly related to systematic behavior in large-scale weather systems and/or the local air-land-sea interaction at this site.
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| 6. |
- Elgered, Gunnar, 1955, et al.
(författare)
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Ground-based microwave radiometry and long-term observations of atmospheric water vapor
- 1998
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Ingår i: Radio Science. - 0048-6604 .- 1944-799X. ; 33:3, s. 707-717
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Tidskriftsartikel (refereegranskat)abstract
- Microwave radiometer data and radiosonde data from the time period 1981-1995 have been used to study long-term trends in the integrated precipitable water vapor (IPWV). The two instruments have operated 37 km apart on the Swedish west coast. Model parameters are estimated for the entire data sets as well as for subsets of the data. The IPWV model parameters are a mean value, a linear drift with time, and the amplitude and phase of an annual component. The radiosonde data, which are uniformly sampled in time, show an increase in the IPWV of 0.03 mm/yr with a statistical standard deviation of 0.01 mm. The microwave radiometer data, which are not at all uniformly sampled in time, show -0.02+/-0.01 mm/yr. We show that the disagreement is caused by the different sampling of the data for the two instruments. When the two data sets are reduced to include only data that are sampled simultaneously, we find an agreement between all estimated model parameters, given their statistical uncertainties. This suggests that if the microwave radiometer had also been operating continuously over the 15-year period, its data would have implied a linear trend similar to the result obtained from the radiosonde data. The general quality of the data, in terms of the short time scatter, has been improved over the time period. The root mean square (RMS) difference between the IPWV measured by the radiometer and by the radiosondes was 2.1 mm during the first 5 years and was reduced to 1.6 mm during the last 4 years. These values include the real difference in the IPWV between the two sites. The bias, radiometer-radiosonde, was 0.1 mm for the whole data set and varied between -0.2 and 0.9 mm for smaller data sets of a few years.
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| 7. |
- Elgered, Gunnar, 1955, et al.
(författare)
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Measurements of atmospheric water vapor with microwave radiometry
- 1982
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Ingår i: Radio Science. - 0048-6604 .- 1944-799X. ; 17:5, s. 1258-1264
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Tidskriftsartikel (refereegranskat)abstract
- A dual-channel, ground-based microwave radiometer, working at the frequencies 21.0 and 31.4 GHz, an infrared spectral hygrometer, and radiosondes have been used for comparative measurements of the integrated amount of precipitable water vapor in the atmosphere over a period with zenith water vapor contents varying between 6 and 26 mm. The microwave radiometer was found to give comparable or better formal accuracy than the radiosondes, the absolute accuracy of which is believed to be about 1 mm. The rms difference of the integrated amount of water vapor in the zenith direction measured with the microwave radiometer and with radiosondes was 1.2 mm for all data, and 0.8 mm for a selected group of good weather data. These are lower formal errors than previously reported. It is shown that the simplified relation between the radiometer antenna termperatures and the integrated amount of water vapor in this case contributes with a formal error of about 0.3 mm. It is suggested that mean ground weather data can be used to adapt this relation to other sites and seasons.
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| 8. |
- Ellgardt, Anders, 1978-, et al.
(författare)
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A study of edge effects in triangular grid tapered-slot arrays using coupling coefficients
- 2010
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Ingår i: Radio Science. - 0048-6604 .- 1944-799X. ; 45, s. RS2005-
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Tidskriftsartikel (refereegranskat)abstract
- Edge effects for tapered-slot elements in triangular grid array antennas are studied by using finite difference time domain codes. The S parameters for finite-by-infinite arrays are computed and evaluated for two different edge models and, to evaluate the edge effects, the results are compared with the S parameters for the infinite array. As expected, the largest difference between the results occurs for the elements closest to the edges, because of the missing coupling from nearby elements and the perturbed element currents due to the edge geometry. By using the proposed method it is possible to distinguish between these two edge effects. A method to combine the finite-by-infinite array results and the infinite array results is presented and used to characterize the perturbation caused by the truncation of the infinite array.
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| 9. |
- Enstedt, M., et al.
(författare)
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A spectral expansion-based Fourier split-step method for uncertainty quantification of the propagation factor in a stochastic environment
- 2016
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Ingår i: Radio Science. - 0048-6604. ; 51:11, s. 1783-1791
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Tidskriftsartikel (refereegranskat)abstract
- A chaos expanded Fourier split-step method is derived and applied to a narrow-angle parabolic equation. The parabolic equation has earlier been used to study deterministic settings. In this paper we develop a spectral-based Fourier split-step method that will take a limited degree of information about the environment into account. Our main focus is on proposing an efficient method for computational electromagnetics in stochastic settings. In this paper we study electromagnetic wave propagation in the troposphere in the case when the refraction index belongs to a uniform distribution.
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| 10. |
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