摘要:

A transmission grating can be used as a frequency scanned antenna, provided most of the incident power is transferred to the diffracted mode, i.e., the grating is blazed. A design procedure for blazing a rectangular bar transmission grating is presented. The performance of a number of gratings is presented. Efficiencies in excess of 99% can be obtained at a single frequency. A scan range of 55° between 3‐dB points can be obtain

ISSN:0048-6604    

DOI:10.1029/RS018i004p00513

年代:1983

数据来源: WILEY

摘要:

The TM electromagnetic wave propagation along a strip grating above an impedance plane is studied. The problem is formulated in terms of a modified Riemann‐Hilbert problem. The modal equation of the structure is derived and solved numerically. Surface wave and leaky wave modes are identified. The phase velocity and attenuation constant of the dominant leaky wave modes are presented, and their dependence on frequency and geometrical parameters is discussed. The possibility of applying this structure to the design of a leaky‐wave antenna is sugges

ISSN:0048-6604    

DOI:10.1029/RS018i004p00519

年代:1983

数据来源: WILEY

摘要:

Numerical results previously obtained by Miyagi and Nishida on the propagation characteristics of stationary TM waves in nonlinear self‐focusing media are shown to have simple analytic form

ISSN:0048-6604    

DOI:10.1029/RS018i004p00532

年代:1983

数据来源: WILEY

摘要:

The quadratic approximation for the phase structure function is used to obtain the two‐frequency mutual coherence function Γ(Δρ, Δω) for spherical wave propagation through a finite slab with transmitter and receiver located in free space on opposite sides of the slab. General analytic solutions are derived for two cases. In the first case the random slab is represented by a one‐dimensional power spectrum of electron density fluctuations corresponding to propagation through elongated irregularities as would occur for an equatorial satellite link to a ground station. In the second case the random slab consists of isotropic ionization irregularities. Both cases taken together represent the extremes of the range of results to be expected for propagation through ionospheric fluctuations, solar wind irregularities, or ionization irregularities caused by barium cloud instabilities. For both cases the complex general analytic results are simplified by use of the thin phase screen approximation to obtain useful analytic expressions for Γ as well as the resulting impulse response function. It is shown that the impulse response to a transmitted power delta function reduces to an exponential form in the limit of strong diffraction and to a Gaussian form in the geometrical optics limit. The Gaussian form corresponds to pulse wander while the exponential form corresponds to diffractive spreading produced by multipath effects. The relationship between the generalized power spectrum and the impulse response function is given, and results are presented for the mean time delay and time delay jitter. The accuracy of the thin phase screen calculation of these quantities is investigated

ISSN:0048-6604    

DOI:10.1029/RS018i004p00535

年代:1983

数据来源: WILEY

摘要:

The scintillation index for weak atmospheric turbulence is formulated for a partially coherent source (in space and time). We obtain results for two cases when the detector has a slow and a fast response time. Our solutions correctly reduce to the known scintillation index in the limit of coherent and incoherent sources. Transmitter aperture averaging and frequency averaging effects are shown as special cases of our results. The limitations of the source model used and the solution obtained for a fast detector are discussed.

ISSN:0048-6604    

DOI:10.1029/RS018i004p00551

年代:1983

数据来源: WILEY

摘要:

A vegetation layer is modeled by a collection of randomly oriented circular discs over a half space. The backscattering coefficient from such a half space is computed using the radiative transfer theory. It is shown that significantly different results are obtained from this theory as compared with some earlier investigations using the same modeling approach but with restricted disc orientations. In particular, the backscattered cross‐polarized returns cannot have a fast increasing angular trend which is inconsistent with measurements. By setting the appropriate angle of orientation to zero the theory reduces to previously published results. Comparisons are shown with measurements taken from milo, corn and wheat and good agreements are obtained for both polarized and cross‐polarized retu

ISSN:0048-6604    

DOI:10.1029/RS018i004p00557

年代:1983

数据来源: WILEY

摘要:

Expressions for the shadow functions are derived for a broad class of non‐Gaussian rough surfaces for which decorrelation of the surface heights implies statistical independence. The numerical results obtained for the backscatter shadow functions are compared with the shadow function for Gaussian surfaces and with recently published results for surfaces with an exponential joint height probability density that does not become statistically independent as the surface heights decorrelate. Contrary to earlier published results, it is shown that even for surfaces with large mean square slopes, the shadow function is not very sensitive to the precise form of the surface height density function assumed. This, however, does not mean that the rough surface scattering cross sections are insensitive to the assumed non‐Gaussian surface height probability dens

ISSN:0048-6604    

DOI:10.1029/RS018i004p00566

年代:1983

数据来源: WILEY

摘要:

A version of the hybrid (ray mode) representation of wave fields has been suggested which is convenient with refractive index profiles corresponding to simultaneously existing surface and elevated ducts. The field at the reception point is represented as a sum of normal modes peculiar to an isolated surface duct and an assembly of rays reflected from the elevated layer.

ISSN:0048-6604    

DOI:10.1029/RS018i004p00573

年代:1983

数据来源: WILEY

摘要:

Diversity systems are foreseen for earth to satellite links operating at frequencies above 10 GHz in localities with high rain‐induced attenuation. The paper discusses orbital diversity, which uses two satellites and an earth receiving site, through an analytical model for the rainfall random process. The model uses rain gauge measurements and radar‐derived information on the slant structure; it gives results that are similar to experimental data and physically meaningful. A comparison is also carried out with corresponding site diversity, and the procedure for computing both attenuation statistics is given. It is shown that orbital diversity may replace site diversity as far as rain attenuation is concerned and may give the same performance up to a certain limit of geometry which depends little on attenuation. It is also shown that site diversity gain can be converted to orbital diversity gain and that the geometrical parameters (site separation and angle aperture) which yield this conversion are related by linear relationships, which are independent of freque

ISSN:0048-6604    

DOI:10.1029/RS018i004p00583

年代:1983

数据来源: WILEY

摘要:

A renormalization technique, employed in the spirit of the formal theory of scattering, is applied to the problem of ionospheric scintillations. In the forward scattering limit, using a Markov approximation for ionospheric fluctuations and renormalized moment equations, one derives the wave statistics for a plane wave or beam propagating through the ionosphere. Fluctuations in the latter are described by an arbitrary power spectrum. Peaks superposed on a power law spectrum are found to increase the scintillation indexS4, and a focusing effect is observed in the strong scintillation limit. An experimental power spectrum, obtained from in situ measurements by the Explorer E satellite and corresponding to electron density fluctuations of 20%, is used to calculateS4for nighttime equatorial scintillations. For an ionospheric slab model 200 km thick at an altitude of 300 km, numerical calculations yield anS4of about 1.1, in approximate agreement with measurements of Basu.

ISSN:0048-6604    

DOI:10.1029/RS018i004p00589

年代:1983

数据来源: WILEY