The document discusses several factors that affect space wave propagation: 1. Curvature of the earth and its imperfections can create shadow zones and reduce transmission distance. 2. The earth's roughness and imperfections cause the amplitude of the ground reflected wave to be smaller than the direct ray. 3. Hills, buildings, and other obstacles can obstruct the radio path between transmitter and receiver. 4. The field strength varies with height above the earth, exhibiting maxima, minima and nulls depending on frequency, transmitter height, and wave polarization.

1. Considerations in Space Wave
Propagation
• Curvature of the earth
• Earth’s imperfection & roughness
• Hills tall buildings & other obstacles
• Height above the earth
• Transition between ground & space wave
• Polarization of the wave.

2. Curvature of the earth
• The field strength becomes small as direct ray
may not be able to reach the receiving antenna.
• The curvature of the earth creates shadow zones.
Shadow zone also called diffraction zone.
• It reduces the possible distance of transmission
• The field strength available at the receiver
becomes small
• E= (2Eo/d) Sin(2πhthr/λd)

5. Earth’s imperfection & roughness
• Earth is basically imperfect & electrically rough
• For the perfect earth reflection coefficient is
unity. But actual earth makes it different from
unity.
• From imperfect earth reflection phase change
different from 180 degree
• The amplitude of the ground reflected wave is
smaller than the direct ray.
• So, the field at the receiving point due to space
wave is reduced by earth’s imperfection &
roughness.

6. Hills tall buildings & other obstacles

7. Height above the earth
• The field varies with height above the earth
• The field variation is characterised by
presence of maxima, minima & nulls.
• The maxima & minima depends on frequency,
height of transmitting antenna, ground
characteristics & polarization of the wave.
• The variation of the field with height is shown.

8. Height above the earth

9. Transition between ground & space
wave
• When the transmitting antenna close to the
earth, ground wave exists & field strength is
independent of the height of the antenna.
• The antenna height has the effect on field
strength & direct & ground reflected rays
predominate over the ground wave.
• Its effect depends on the frequency, polarization
& constant of the earth.
• At higher heights of antennas, space wave
dominates

10. Polarization of the wave.
• It depends on the angle of incidence for 0 to 90 degree
the magnitude of the reflected wave will be less with
vertical polarization than the horizontal polarization.
• This reduces the amplitude of the ground reflected
wave
• The electromagnetic interference created by ignition
system, domestic & consumer electrical, electronic &
communication equipments & so on is in general
vertically polarized. Horizontal polarization is useful for
discrimination against these disturbances occurring in
TV & FM broadcating.

11. Atmospheric effects in space wave
propagation
• The atmosphere consists of gas molecule & water
vapour. This causes the dielectric constant slightly
greater than unity.
• The density of air & water vapour vary with
height. As a result dielectric constant & refractive
index of air depends on height.
• Dielectric constant decreases with height.
• The variation of refractive index with height gives
rise to different phenomena like refraction,
reflection, scattering, duct propagation & fading.

13. 3. Refraction, which occurs when a wave passes through an
interface and the angle of the wave vector is changed. We will
be most interested in how the atmosphere refracts and bends
radio waves, enabling over-the-horizon communications.
4. Scattering, which occurs when radio signals are reacted of
objects much smaller than a wavelength, and the density of
objects may be fairly high. For example, scattering o of rain
drops, which in an aggregate sense leads to large-scale
frequency-dependent attenuation of radio signals.

14. Plane-Earth Reection
1. Reflection, which occurs when a wave impinges on an object
with large dimensions relative to a wavelength. The surface of
the earth, and large buildings are examples.
2. Disfraction, which occurs when an object with sharp edges or
irregularities obstructs the
radio path between the transmitter and receiver. The edges
influence the propagation of the waves around the obstacle.

15. Other Impairments
Atmospheric absorption – water vapor and oxygen contribute to attenuation
Multipath – obstacles reflect signals so that multiple copies with varying delays are
received
Refraction – bending of radio waves as they propagate through the atmosphere

16. Multipath Propagation

17. The Effects of Multipath
Propagation
Multiple copies of a signal may arrive at different phases
If phases add destructively, the signal level relative to noise declines, making
detection more difficult
Intersymbol interference (ISI)
One or more delayed copies of a pulse may arrive at the same time as the primary
pulse for a subsequent bit

18. Multipath Propagation
Reflection - occurs when signal encounters a surface that is large
relative to the wavelength of the signal
Diffraction - occurs at the edge of an impenetrable body that is
large compared to wavelength of radio wave
Scattering – occurs when incoming signal hits an object whose
size in the order of the wavelength of the signal or less

21. Duct Propagation

23. Radio Horizon

24. Radio Horizon

26. Radio Horizon

27. Troposcatter

28. Fading of EM waves in Troposphere
• Fading is signal loss due to change in electrical
characteristics of troposphere.
• Because of variation in dielectric constant
• Presence of eddies
• Uneven variation of refractive index
• Variation of effective earth radius factor, K