---
title: "Surface wave propagation pros and cons"
subject: "Propagation and Antenna"
chapter: 4
key: "semester_6/propagation_and_antenna:surface-wave-propagation"
source: https://www.bctengineer.com/q/semester_6/propagation_and_antenna/surface-wave-propagation
site: BCT Engineering
---

# Surface wave propagation pros and cons

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

- Asked in: 2081 Chaitra, 5+4 marks
- Video: [Ground Wave Propagation (Definition, Basics, Frequency Range, Advantages & Disadvantages) Explained](https://www.youtube.com/watch?v=V4zuFsME6pg) — Engineering Funda
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/propagation_and_antenna/surface-wave-propagation
- Whole chapter: https://www.bctengineer.com/md/semester_6/propagation_and_antenna/chapter-4

## Question

Explain the surface wave propagation. Write its major advantages and disadvantages.

## Short answer

Surface wave propagates with vertical polarization, guided by lossy ground, following earth's curvature. Used at VLF to MF. Advantages: stable day-and-night signal, no line-of-sight limitation, penetrates seawater. Disadvantages: restricted to low frequencies (low bandwidth), requires tall vertical antennas and extensive ground systems, high transmitter power, high atmospheric noise.

## Answer

**Surface wave propagation** is the mode in which a vertically polarised wave travels along the surface of the earth, following its curvature. The earth acts as a lossy guiding boundary: the wave induces charges and currents in the ground, which keep it attached to the surface. It is the main mode for VLF, LF and MF (up to about 2–3 MHz).

```text
     wave front tilts forward (wave tilt)
       |  /  /  /  /
       | /  /  /  /    → direction of travel
  Tx  /|/  /  /  /
 ====|==================================
  ~~~~ induced earth currents (loss) ~~~~
```

#### Explanation
- **Vertical polarisation** is necessary; a horizontally polarised wave is short-circuited by the conducting ground and dies out quickly.
- **Wave tilt:** energy is lost into the ground, so the wave front tilts forward. The E-field gains a horizontal component that drives power down into the earth. Tilt is larger for poor ground.
- **Attenuation:** field strength is approximately
```text
E = A · E₀ / d
```
  where E₀/d is the unattenuated (inverse-distance) field and A (< 1) is the ground attenuation factor, found from Sommerfeld/Norton curves using the "numerical distance". A falls faster with:
  - higher frequency (loss increases rapidly with f),
  - lower ground conductivity σ and permittivity εr,
  - longer distance.
- **Diffraction:** the wave bends around the earth's curvature by diffraction, more easily at long wavelengths, which is why low frequencies travel far.
- **Ground type:** sea water (σ ≈ 4 S/m) gives the longest range; moist soil is medium; dry and rocky land is poor.
- Range: VLF/LF up to 1000+ km; MF ≈ 100–300 km; HF only tens of km.

#### Advantages
1. Stable, reliable signal with no fading (no ionospheric dependence).
2. Works day and night, in all seasons.
3. Not limited by line of sight; follows earth's curvature.
4. VLF waves penetrate sea water, useful for submarine communication.
5. Simple receiving arrangements; good for local and regional broadcast (AM).

#### Disadvantages
1. Usable only at low frequencies (below ≈ 3 MHz), so bandwidth is very small.
2. Requires very tall vertical antennas (λ/4 is 75 m at 1 MHz) and extensive ground systems.
3. High transmitter power needed because of ground losses.
4. Range falls sharply with frequency and over poor soil.
5. Atmospheric noise is high at LF/MF.

## Check yourself

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

1. Why must a surface wave be vertically polarised?
   A. Vertical waves are not diffracted
   B. A horizontally polarised wave is short-circuited by the conducting ground and dies out
   C. Horizontal waves are absorbed by the ionosphere
   D. Vertical waves have higher frequency
   Answer: B. The ground shorts the horizontal E-field, while the vertical field keeps the wave attached. (Key point: Polarisation)

2. Wave tilt in surface wave propagation is:
   A. The forward lean of the wave front as energy is lost into the ground
   B. Rotation of polarisation by the ionosphere
   C. Reflection at the D layer
   D. Bending upward away from earth
   Answer: A. The horizontal E-component drives power into the earth; tilt is larger for poor ground. (Key point: Wave tilt)

3. Surface-wave attenuation increases with:
   A. Lower frequency
   B. Higher ground conductivity
   C. Higher frequency, lower ground conductivity, longer distance
   D. Shorter distance
   Answer: C. Loss grows rapidly with f and is least over sea water. (Key point: Attenuation factors)

4. A major disadvantage of surface wave propagation is:
   A. It fades heavily with the ionosphere
   B. It needs low frequencies, so tall antennas, high power and small bandwidth
   C. It works only at night
   D. It cannot follow earth's curvature
   Answer: B. It is stable and day/night independent, but limited to below about 3 MHz with big antennas and ground losses. (Key point: Disadvantage)

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