---
title: "Marconi antenna characteristics"
subject: "Propagation and Antenna"
chapter: 3
key: "semester_6/propagation_and_antenna:marconi-antenna"
source: https://www.bctengineer.com/q/semester_6/propagation_and_antenna/marconi-antenna
site: BCT Engineering
---

# Marconi antenna characteristics

Propagation and Antenna · Chapter 3: Antenna Classification

- Asked in: 2077 Chaitra, 4 marks; 2075 Bhadra, 4 marks; 2075 Baisakh, 6 marks; 2073 Magh, 4 marks; 2072 Asoj, 3 marks (asked 5 times)
- Video: [Marconi Antenna](https://www.youtube.com/watch?v=SQ2_j2ZBwa8) — Stan Gibilisco
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/propagation_and_antenna/marconi-antenna
- Whole chapter: https://www.bctengineer.com/md/semester_6/propagation_and_antenna/chapter-3

## Question

Explain the major characteristics of Marconi antenna with necessary figures.

## Short answer

Marconi antenna is a λ/4 vertical monopole grounded at base; ground plane creates image forming equivalent λ/2 dipole in upper half-space. Characteristics: omnidirectional horizontal pattern, maximum radiation along ground, vertical polarization, 36.5Ω radiation resistance, 5.15 dBi directivity, requires good ground system (radials/counterpoise), often top-loaded at MF to reduce height.

## Answer

A **Marconi antenna** is a vertical **quarter-wave (λ/4) monopole** whose lower end is connected to ground through the transmitter. The conducting earth produces an **image** of the antenna, so a λ/4 monopole behaves like a λ/2 dipole (Hertz antenna) in the upper half-space.

```text
      ^  I = 0 (top)
      |  current
 λ/4  |  distribution        Pattern (vertical plane)
      |  max at base               _ _
      |                         .'  |  '.
  ~ TX|________ ground       __/____|____\__ ground
 ////////////////////////     max along ground,
   image (λ/4) below          null overhead
```

#### Major characteristics

1. **Length**: λ/4 physical height; the image supplies the other λ/4.
2. **Current distribution**: maximum at the base (feed), zero at the top; voltage maximum at the top.
3. **Radiation pattern**: same as the upper half of a half-wave dipole; **omnidirectional** in the horizontal plane, maximum along the ground, null overhead.
4. **Polarization**: vertical, ideal for **ground-wave** propagation at LF/MF.
5. **Input (radiation) resistance**: ≈ 36.5 Ω, half of a dipole's 73 Ω, because it radiates into a half space only.
6. **Directivity**: 3.28 (5.15 dBi), double that of a half-wave dipole, since power goes into half space.
7. **Ground system**: needs good earth; buried radial wires, or a **counterpoise** (wire mesh above ground) where soil is poor. Ground loss reduces efficiency.
8. **Height reduction**: at MF, λ/4 is tall (e.g. 75 m at 1 MHz), so **top loading** (capacitance hat, T or inverted-L) or base loading coil is used.

#### Marconi vs Hertz

| Point | Marconi | Hertz |
|---|---|---|
| Length | λ/4 | λ/2 |
| Ground | Grounded, needs good earth | Ungrounded |
| R_rad | 36.5 Ω | 73 Ω |
| Use | MF/LF broadcast | HF and above |

**Applications**: AM (MF) broadcasting towers, car whip antennas, mobile and handheld radios.

## Check yourself

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

1. Why does a lambda/4 Marconi monopole behave like a lambda/2 dipole in the upper half-space?
   A. The conducting earth produces an image supplying the other lambda/4
   B. The monopole is secretly lambda/2 long
   C. The earth absorbs half the current
   D. It is fed with double power
   Answer: A. The ground image acts as the missing lower half of a dipole. (Key point: Image principle)

2. The current in a Marconi antenna is
   A. zero at the base and maximum at the top
   B. maximum at the base and zero at the top
   C. uniform along its length
   D. maximum at the centre only
   Answer: B. Current is maximum at the feed and zero at the open top, where voltage is maximum. (Key point: Current distribution)

3. The radiation resistance of a Marconi antenna is about
   A. 73 ohm
   B. 146 ohm
   C. 36.5 ohm
   D. 377 ohm
   Answer: C. It radiates into half space only, so it is half the 73 ohm of a half-wave dipole. (Key point: Radiation resistance)

4. Directivity of a Marconi monopole is 3.28, which is
   A. half that of a dipole
   B. equal to a dipole
   C. unrelated to the ground
   D. double that of a half-wave dipole because power goes into half space
   Answer: D. Same power concentrated into half space doubles directivity from 1.64 to 3.28. (Key point: Directivity)

## Related in Propagation and Antenna

- [Marconi antenna working and design](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Amarconi-working-design) — Propagation and Antenna, chapter 3
- [Single wire radiation and omnidirectional antenna characteristics](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Asingle-wire-radiation-omnidirectional) — Propagation and Antenna, chapter 1
- [Rhombic antenna construction and working](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Arhombic-antenna) — Propagation and Antenna, chapter 3, asked 5×
- [V antenna construction and working](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Av-antenna) — Propagation and Antenna, chapter 3, asked 4×
- [UHF band and log-periodic antenna](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Auhf-band-log-periodic) — Propagation and Antenna, chapter 3
- [RF spectrum; VHF and UHF characteristics](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Arf-spectrum-vhf-uhf) — Propagation and Antenna, chapter 4

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