摘要:

The major obstacle in utilizing recently allocated frequency bands in the mm‐wave spectrum for earth‐satellite communications is rain attenuation. Since heavy rain is generally quite localized it has been proposed that the required reliability could be achieved through path diversity, which requires two or more earth receiving terminals. This paper describes a year‐long diversity experiment in the Boston area involving two sun trackers separated by 7 mi and operating at 3

ISSN:0048-6604    

DOI:10.1029/RS008i001p00001

年代:1973

数据来源: WILEY

摘要:

Experimental height‐gain data for the magnitude of electromagnetic groundwaves propagating over flat homogeneous paths were obtained by microwave (4.765 GHz) modeling. The experimental results were compared with height‐gain theory, and the limitations of the theory were established in terms of surface impedance, height of the receiving point, and antenna separation distance. Earlier experimental studies of this problem have not been entirely conclusive due to an inadequate knowledge of the surface impedance and the influence of the surface upon the antenna impedance. Here, extensive corrective measures were taken to eliminate or account for these effects.It is concluded that the theory for the total field is remarkably accurate as the height above or distance along the surface is varied, even at distances as close as 2λ0from the source. Furthermore, the question as to the choice between the various forms of numerical distance seems academic. The restriction on height above the surface is eliminated, and the restriction upon the magnitude of the surface impedance is relaxed depending upon the presence of a significant trapped surface wave.Part 2 is a companion paper which relates the homogeneous path height‐gain to mixed‐path experimental measurements versus height and

ISSN:0048-6604    

DOI:10.1029/RS008i001p00007

年代:1973

数据来源: WILEY

摘要:

Analytical as well as experimental height‐gain studies for mixed‐path groundwave propagation are virtually nonexistent. Therefore, it was shown how the theoretical height‐gain for a homogeneous path relates to heterogeneous‐path experimental measurements versus height and distance. The results show that the magnitude of a groundwave field which crosses an abrupt boundary rapidly acquires the characteristic properties of the second medium, and the field over a heterogeneous surface attenuates at essentially the same rate as the field on the surface. The groundwave which has crossed an abrupt boundary can be predicted for small heights above the surface by simply multiplying the well‐established mixed‐path theory for antennas located on the surface by appropriate homogeneous‐path height‐gain factors corresponding to the local surface impedance, provided the field is predominantly

ISSN:0048-6604    

DOI:10.1029/RS008i001p00017

年代:1973

数据来源: WILEY

摘要:

An experimental program to measurein‐situvalues of the electrical resistivity and surface impedance of sea ice at VLF was carried out at Point Barrow, Alaska. Temperature, salinity, and resistivity were measured as a function of depth in the ice for both first‐year and multiyear sea ice by means of cored samples. All three quantities varied with the age of the ice, and, in addition, the resistivity varied with age from 102ohm m to 104ohm m at the surface and in general down to a few ohm m at the sea‐water interface.The wavetilt of a VLF plane wave propagating over sea ice is theoretically linearly dependent on the thickness. Measurements of the quadrature phase wavetilt at 18.6 kHz give values that are of the right order of magnitude but erratic in local behavior. Short‐spacing Wenner array resistivity measurements and telluric current measurements at VLF demonstrated that the erratic behavior was due to significant horizontal variations of the sea‐ice resistivity over distances o

ISSN:0048-6604    

DOI:10.1029/RS008i001p00023

年代:1973

数据来源: WILEY

摘要:

Computations are made of the forward‐ and back‐scattering intensities of oblate spheroidal raindrops at 19.3 and 34.8 GHz, assuming plane waves at normal incidence to the drop axis. Two kinds of polarization are considered in the incident field: one is parallel to drop axis; the other is perpendicular. Numerical values of these basic scattering intensities are listed in tables. Forward‐scattering intensities are then used for determining the effective propagation constants of rain‐filled space. From these propagation constants, attenuations and phase rotations for parallel and perpendicular polarizations are computed for several rain rates. One significant conclusion is that the difference between phase rotations in the two polarizations at 19.3 GHz becomes very large as the rain rate increases, whereas that at 34.8 GHz is bounded in a very small range throughout all possible rai

ISSN:0048-6604    

DOI:10.1029/RS008i001p00031

年代:1973

数据来源: WILEY

摘要:

A new technique has been developed for measuring irregularity structure and velocity in the ionosphericEandFregions. The Arecibo incoherent‐scatter radar was modified to measure electron‐density profiles simultaneously with two beams: one fixed beam pointed at the zenith, and a second beam could be varied over 360° in azimuth and from 2 to 20° in zenith angle. Fluctuations in ionization density were observed to drift from one beam to the other so that information was obtained about both the horizontal velocity and the structure of these disturbances. Velocities of 100 to 200 m sec−1and horizontal scale sizes of 50 to 100 km were deduced for theEregion and roughly 400 m sec−1and 500 km for theFregion. A plot of velocity versus altitude shows a spiral structure with a vertical wavelength of 20 to 30 km in t

ISSN:0048-6604    

DOI:10.1029/RS008i001p00039

年代:1973

数据来源: WILEY

摘要:

FollowingCicerone and Bowhill[1970a, b, 1971] a Monte Carlo method is adopted as a basis for the derivation of the photoelectron‐heat input into the ionospheric plasma. Considering that the size of the source elements must be small compared with the range over which photoelectrons dissipate their energy, a great number of Monte Carlo runs are required normally for the computation of the heating rates. This approach is modified in an attempt to minimize the computation time. The heat‐input distributions are computed for arbitrarily small source elements that are spaced apart at distances corresponding to the photoelectron dissipation range. By means of a nonlinear interpolation procedure their individual heating‐rate distributions are utilized to produce synthetic ones that fill the gaps between the Monte Carlo generated distributions. By varying these gaps and the corresponding number of Monte Carlo runs the accuracy of the results is tested to verify the validity of this procedure. It is concluded that this model can reduce the computation time by as much as an order of magnitude, thus improving the feasibility of including Monte Carlo calculations in self‐consistent ionosphere

ISSN:0048-6604    

DOI:10.1029/RS008i001p00047

年代:1973

数据来源: WILEY

摘要:

A convenient ω‐θè plot for the group index of refraction is introduced for studying the radiated field from transient current sources of arbitary orientations in anisotropic cold plasmas. The plot is valid not only for the far zone, but also for the near zone with large time. Typical numerical examples are given to provide the quantitative insight of the transient response in anisotropic cold pla

ISSN:0048-6604    

DOI:10.1029/RS008i001p00051

年代:1973

数据来源: WILEY

摘要:

The radiation of an arbitrary source in a stratified system including anisotropic slabs is considered. Starting from an abstract‐operator formulation given byBresler and Marcuvitz[1956, 1957], the transverse field is evaluated by using a Fourier‐integral representation. The Green's function is expressed through the evaluation of the source‐free solutions. The scattered field and the plane‐wave response are examined. An example is given concerning the field radiated in the presence of an anisotropic ferrite slab. The far field is evaluated through a saddle‐point in

ISSN:0048-6604    

DOI:10.1029/RS008i001p00063

年代:1973

数据来源: WILEY

摘要:

The problem of diffraction of anE‐polarized plane wave by a perfectly conducting wedge, having the illuminated side loaded with a thin dielectric slab of which the relative permittivity is not much larger than unity, is treated. The solution is given in an integral form, consisting of geometrical optics and associated diffraction terms, by applying an approximate boundary condition at the dielectric surface. The diffraction integrals involved are evaluated asymptotically in terms of Fresnel's integrals. Using the reciprocity principle, the results are extended to the cylindrical‐wave excitation. The validity of the results is verified by comparison with experiment for the case of a dipole‐fed dielectric‐loade

ISSN:0048-6604    

DOI:10.1029/RS008i001p00071

年代:1973

数据来源: WILEY