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Short note: Tropospheric scatter propagation

Short answer

Tropospheric scatter propagates UHF/microwaves beyond line-of-sight by scattering from tropospheric irregularities in a common volume. Range 100–800 km, requires high power, large antennas, and diversity reception due to Rayleigh fading, offering reliable relay without ionospheric dependence.

Write a short note on tropospheric scatter propagation.

Tropospheric scatter (troposcatter) is beyond-the-horizon propagation in which UHF and microwave signals (about 300 MHz to 10 GHz) are scattered by small irregularities (turbulence and refractive index blobs) in the troposphere, so that a small part of the energy reaches a receiver beyond the radio horizon.

          common (scatter) volume
                 .:::::.
               /  :::::  \
   beam      /             \     beam
   Tx dish /                 \  Rx dish
   =======(==== earth bulge ====)=====
          |<-- 100 to 800 km -->|

Working: two high-gain antennas aim their beams just above the horizon so that the beams intersect in a common volume in the troposphere (height a few km). Turbulent eddies there scatter a small fraction of the energy forward to the receiver.

Features

  • Range 100–800 km, beyond LOS, without repeaters or satellites.
  • Very high path loss, so high power (kW) transmitters, large dish antennas (gain 40–50 dB) and sensitive receivers are needed.
  • Signal suffers Rayleigh fading (fast) and slow fading; diversity (space, frequency) is used.
  • Limited bandwidth because of multipath delay spread.
  • Reliable regardless of ionospheric conditions; not affected by solar disturbances.
  • Uses: military and remote links, offshore platforms, links across mountains or sea.

✓ Answer checked by Claude Opus 5.5 (high effort)

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