---
title: "Short note: Tropospheric scatter propagation"
subject: "Propagation and Antenna"
chapter: 4
key: "semester_6/propagation_and_antenna:tropospheric-scatter-short-note"
source: https://www.bctengineer.com/q/semester_6/propagation_and_antenna/tropospheric-scatter-short-note
site: BCT Engineering
---

# Short note: Tropospheric scatter propagation

Propagation and Antenna · Chapter 4: Propagation and Radio Frequency Spectrum

- Asked in: 2073 Bhadra, 3 marks
- Video: [Tropospheric Scatter Propagation Simplified |Antenna & Wave Propagation Mod-6|Wireless Communication](https://www.youtube.com/watch?v=k4_wjZm2d88) — THE BACKBENCH ENGINEERING COMMUNITY
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/propagation_and_antenna/tropospheric-scatter-short-note
- Whole chapter: https://www.bctengineer.com/md/semester_6/propagation_and_antenna/chapter-4

## Question

Write a short note on 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.

## Answer

**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.

```text
          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.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. How does tropospheric scatter reach beyond the horizon?
   A. Reflection from the E layer
   B. Scattering by turbulent refractive-index irregularities in a common volume
   C. Diffraction around the earth
   D. Trapping in a duct
   Answer: B. Two beams intersect in a common troposphere volume where turbulence scatters a small part of energy forward. (Key point: Mechanism)

2. Why do troposcatter links need high power and large dishes?
   A. Path loss is very high because only a small fraction is scattered
   B. The ionosphere absorbs the signal
   C. They use HF frequencies
   D. The range is only a few km
   Answer: A. Only a small part of the energy is scattered, so kW transmitters and 40-50 dB gain antennas are used. (Key point: System requirements)

3. Which fading and remedy are associated with troposcatter?
   A. Rayleigh fading; diversity reception
   B. No fading; none needed
   C. Faraday fading; polarisation change
   D. Skip fading; frequency change
   Answer: A. Multipath in the scatter volume causes Rayleigh and slow fading, reduced by space or frequency diversity. (Key point: Fading)

## Related in Propagation and Antenna

- [Tropospheric range: 100 ft and 50 ft antennas](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Atropospheric-range-numerical) — Propagation and Antenna, chapter 4