---
title: "Ground system in vertical monopole"
subject: "Propagation and Antenna"
chapter: 3
key: "semester_6/propagation_and_antenna:monopole-ground-system"
source: https://www.bctengineer.com/q/semester_6/propagation_and_antenna/monopole-ground-system
site: BCT Engineering
---

# Ground system in vertical monopole

Propagation and Antenna · Chapter 3: Antenna Classification

- Asked in: 2069 Bhadra, 8 marks
- Video: [Effect of ground planes: monopole antennas. | 20/62 | UPV](https://www.youtube.com/watch?v=_tdaIgVTbFw) — Universitat Politècnica de València - UPV
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/propagation_and_antenna/monopole-ground-system
- Whole chapter: https://www.bctengineer.com/md/semester_6/propagation_and_antenna/chapter-3

## Question

Explain the fundamentals as well as importance of ground and ground system construction in vertical monopole antenna.

## Short answer

A vertical monopole uses the ground as a mirror and return path. Lossy soil causes low efficiency. A radial ground system of 60–120 buried λ/4 wires reduces ground resistance to 1–2 Ω, raising efficiency to over 80%; a counterpoise is used where soil is poor.

## Answer

A vertical monopole (Marconi antenna) is fed between the base of a vertical wire and the earth. The earth is a working part of the antenna, so its quality and the **ground system** built under the antenna decide the efficiency.

#### Fundamentals
- **Image action:** a conducting ground acts as a mirror and produces an image of the monopole. The λ/4 monopole plus its image behaves like a λ/2 dipole: Rᵣ ≈ 36.5 Ω, directivity ≈ 3.28 (5.16 dBi), maximum radiation along the ground, vertically polarised.
- **Return current:** the antenna current returns to the base through the ground. Displacement current from the wire enters the ground around the antenna (most within λ/2 of the base) and flows radially back to the base.
- **Ground loss:** the soil has resistance, so this return current produces loss R_g. Efficiency:

```text
η = Rᵣ / (Rᵣ + R_g + R_other)
```
  With Rᵣ only ≈ 36 Ω (much less for short LF/MF masts, sometimes < 5 Ω), even a few ohms of ground loss can waste most of the power.
- **Effect of ground constants:** good conductivity σ (sea water, wet soil) gives a near-perfect image and low loss; dry, sandy or rocky soil gives large loss and lifts the radiation away from the ground, reducing the ground wave.

#### Importance of the ground
1. Completes the circuit of the antenna (acts as the second half of the dipole).
2. Decides radiation efficiency and radiation resistance.
3. Shapes the vertical pattern; good ground keeps the beam low along the earth, needed for MF ground-wave service.
4. Gives lightning protection and a stable reference.

#### Ground system construction
```text
   Top view of radial ground system
          \   |   /
        \  \  |  /  /
     ------  (mast) ------   60-120 radials
        /  /  |  \  \        each ≈ λ/4 to λ/2
          /   |   \          buried 15-30 cm
```
1. **Buried radial wires:** 60–120 copper wires (or strips) run out radially from the base, each λ/4 to λ/2 long, buried 15–30 cm deep and joined at the base to a copper ring or plate. 120 radials of λ/4 is the usual broadcast standard; it brings the ground loss down to about 1–2 Ω.
2. **Ground screen / mat:** a copper mesh close around the base where current density is highest.
3. **Counterpoise:** where the soil is rocky, sandy or dry, a network of wires is stretched 2–4 m **above** the ground, insulated from earth, under the antenna. It acts as a capacitor plate and provides a low-loss return path.
4. **Earth electrodes:** copper rods or plates driven into moist soil, with salt/charcoal treatment, to keep earth resistance low.
5. Over sea water or very wet ground, a simple earth is enough because the soil itself is a good conductor.

A good ground system raises efficiency from 20–30% (poor ground) to over 80–90%, and strengthens the ground-wave field.

## Check yourself

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

1. Why is the ground a working part of a vertical monopole?
   A. It forms the image, making a λ/4 monopole act like a λ/2 dipole, and carries the return current
   B. It is only for lightning protection
   C. It supports the mast
   D. It supplies power
   Answer: A. Image action and the return current through the soil make the earth the second half of the antenna. (Key point: Ground as part of the antenna)

2. With Rr of only a few ohms for a short mast, what does a few ohms of ground resistance do?
   A. Nothing significant
   B. Wastes most of the power because η = Rr/(Rr + Rg + Rother)
   C. Increases directivity
   D. Raises radiation resistance
   Answer: B. Efficiency falls sharply when ground resistance is comparable to Rr. (Key point: Effect of ground loss)

3. What is the typical broadcast radial ground system?
   A. A few 1 m rods
   B. 60-120 buried copper radials each λ/4 to λ/2 long, joined at the base, reducing loss to about 1-2 Ω
   C. One horizontal wire at 10 m height
   D. A plastic sheet
   Answer: B. Many buried radials intercept the return current and lower ground loss; 120 radials of λ/4 is the standard. (Key point: Radial ground system)

4. When and how is a counterpoise used?
   A. On rocky, sandy, dry soil; wires 2-4 m above ground, insulated from earth, acting as a capacitor plate and low-loss return path
   B. Over sea water only
   C. Buried 30 cm deep
   D. To raise the antenna height
   Answer: A. Where radials cannot be buried or soil is poor, an elevated insulated wire network provides the return path. (Key point: Counterpoise)

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