Prolonged space-wave fadeouts in tropospheric propagation

This paper contains results of a measurement program on 751 Mc/s and 9.2 Gc/s using a long mountain-obstacle diffraction path in Colorado. Data are analyzed and evaluated in terms of long· term and short-term variability, correlation coefficients between carrier envelopes received on spaced antennas, and comparison of a priori predicted and measured cumulative distributions of hourly transmission loss medians. Results show beuer agreement between predictions and measurements on 751 Mc/s than on 9.2 Gc/s. Short-term (within-the-hour) variations in signal level on 751 Mc/s can be characterized as prolonged space-wave· fadeouts, whereas such variations on 9.2 Gc/s verv frequently show characteristics of a Rayleigh-distributed signal.

Section: Introductionmentioning

confidence: 91%

Section: -mentioning

confidence: 99%

Section: -mentioning

confidence: 99%

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Mountain Obstacle Diffraction Measurements at 751 Mc/s and 9.2 Gc/s

Barsis

Hause

1966

“…The likelihood of the strong positive gradients which produce diffraction fading depends, of course, upon the location. 1 These gradients are occasionally encountered on oversea or maritime paths (Cabessa, 1955;Ugai, 1961;Barsis and Johnson, 1962). They are rare on paths over mountainous terrain (Klein and Libois, 1953;Troitskii, 1960).…”

Section: Diffraction Fadingmentioning

confidence: 99%

Determination of Antenna Height for Protection Against Microwave Diffraction Fading

Dougherty

Wilkerson

1967

The wide variations in refractive index gradients that may be encountered ·for nominally line-ofsight microwave maritime paths can cause severe fading. A common type is known as k-type fading which includes phase-interference fading and also diffraction fading as the refractive index gradient varies over a wide range. Lewin (1962) was the first to provide an engineering design procedure that roughly approximated: (a), the required terminal antenna heights to reduce diffraction fading, and (b), the required diversity separations (frequency or space) to provide a dynamic reduction of phase-inter· ference fading. The diversity design procedures, (b) above,.bave since been derived in a more accurate manner although they presuppose that item (a) has been provided for. The present paper meets this requirement. It provides a more accurate design procedure for determining the requirements, (a) above, to reduce diffraction fading. As an aid for the procedure, a new computer-derived curve is presented for the attenuation by a spherical earth at grazing conditions.

“…Focusing of waves in naturally occurring ducts (regions of space with appropriate distribution of refractive index) is of considerable importance in tropospheric communications [Bean, 1954;Barsis and Johnson, 1962;Wilkerson, 1962], ionospheric propagation [Carrara et al, 1970], and sound propagation in sea water [e.g., Gordon, 1965, 1970] and atmosphere. The work on tropospheric propagation is essentially qualitative in nature, and the investigations on ionospheric propagation normally resort to numerical computations.…”

Section: Introductionmentioning

confidence: 99%

Focusing of Waves in Ducts

Sodha¹,

Ghatak²,

Tewari³

et al. 1972

This paper presents an investigation of the propagation of cylindrical waves (the field being independent of x) along the z direction inducts described by where c(y, z) is the wave velocity, C0 and ϵ0 are constants, ϵ2(z) is an arbitrary function of z, and ϵ corresponds to the dielectric constant for electromagnetic waves. It has been shown that the intensity A02 of the wave is in general given by where E0 is a constant, yo is a constant, F is an arbitrary function of [y/yoƒ(z)L], and ƒ(z) is a dimensionless beam‐width parameter given by in the geometrical optics approximation. The nature of the variations of ƒ with z has been discussed for some simple profiles of ϵz(z) in the geometrical optics approximation; diffraction has also been taken into account when the beam (F) is Gaussian.