---
title: "Standing vs travelling wave; V antenna"
subject: "Propagation and Antenna"
chapter: 3
key: "semester_6/propagation_and_antenna:standing-travelling-v-antenna"
source: https://www.bctengineer.com/q/semester_6/propagation_and_antenna/standing-travelling-v-antenna
site: BCT Engineering
---

# Standing vs travelling wave; V antenna

Propagation and Antenna · Chapter 3: Antenna Classification

- Asked in: 2073 Magh, 3+5 marks
- Video: [Travelling Wave antenna (Basics, Structure, Operation, Designing, Radiation, Pros & Cons) Explained](https://www.youtube.com/watch?v=xRbf4tNFDnw) — 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/standing-travelling-v-antenna
- Whole chapter: https://www.bctengineer.com/md/semester_6/propagation_and_antenna/chapter-3

## Question

What is the main difference between standing wave antenna and travelling wave antenna? Explain with a neat sketch the construction, working principle and characteristic of V antenna.

## Short answer

Standing wave antennas have open ends, reflections, and narrow bandwidth; travelling wave antennas are terminated, with forward wave only and wide bandwidth. V antenna consists of two long wires forming a V, fed at apex; terminated V is unidirectional and used for HF communication.

## Answer

#### Standing wave vs travelling wave antenna

A **standing wave (resonant) antenna** has its far end open, so the wave reflects and forms standing waves; a **travelling wave (non-resonant) antenna** is terminated in its characteristic impedance, so the wave travels only forward.

| Point | Standing wave (resonant) | Travelling wave (non-resonant) |
|---|---|---|
| End condition | Open circuit | Matched resistive load |
| Waves on wire | Incident + reflected → standing wave | Only forward travelling wave |
| Current | Sinusoidal, with nulls every λ/2 | Nearly uniform amplitude, progressive phase |
| Pattern | Bidirectional (symmetric lobes) | Unidirectional (towards load end) |
| Bandwidth | Narrow, resonant lengths only | Wide |
| Input impedance | Varies strongly with frequency | Nearly constant and resistive |
| Efficiency | Higher (no load loss) | Lower (power lost in load) |
| Examples | λ/2 dipole, resonant V | Beverage, terminated V, rhombic |

#### V antenna: construction

```text
                 leg 1, length l (2λ-8λ)
           /‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾ (R)
  open-  <   apex angle 2θₘ      ===> beam
  wire     \___________________________ (R)
  feeder         leg 2      (R only in non-resonant V)
```

- Two long horizontal wires forming a V, fed at the apex by a 600 Ω balanced line in antiphase.
- Apex angle = 2θₘ, θₘ = main-lobe angle of a long wire, cosθₘ ≈ 1 − 0.371λ/l (e.g. l = 4λ → θₘ ≈ 25°).

#### Working principle

Each leg is a long wire radiating its main lobe at θₘ to the wire. By placing the legs at ±θₘ to the bisector, one main lobe from each leg points along the bisector, where they add in phase; elsewhere they partly cancel. With open ends the V carries standing waves and is bidirectional; with terminated ends it carries travelling waves and is unidirectional.

#### Characteristics

- HF band, horizontal polarization, gain ≈ 3 dB more than a single long wire (≈ 10–15 dBi for long legs).
- Wide bandwidth; input impedance ≈ 500–800 Ω.
- Simple (three poles), but needs large area and has side lobes.
- Used for HF point-to-point communication.

## Check yourself

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

1. Standing vs travelling wave antenna?
   A. Standing: terminated
   B. Standing: open end, reflection; travelling: terminated with matched load
   C. Both terminated
   D. Both open
   Answer: B. Termination absorbs reflection. (Key point: End condition)

2. Which is true of travelling wave antennas?
   A. Higher efficiency
   B. Narrow band, bidirectional
   C. Wide bandwidth, unidirectional, lower efficiency
   D. Varying impedance
   Answer: C. Power is lost in the load. (Key point: Properties)

3. How does V create a beam?
   A. Reflector behind
   B. Legs parallel
   C. Standing waves only
   D. Legs at plus minus theta_m so one lobe per leg aligns along bisector
   Answer: D. Lobes add in phase along the bisector. (Key point: V working)

4. With l = 4 lambda, theta_m approx?
   A. 25 degrees
   B. 45 degrees
   C. 90 degrees
   D. 5 degrees
   Answer: A. cos theta = 1 - 0.371/4 = 0.907, about 25 degrees. (Key point: Example)

## Close variants set in other exams

- [Standing vs travelling wave; Rhombic antenna](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Astanding-travelling-rhombic) — Propagation and Antenna, chapter 3, asked 2×

## Related in Propagation and Antenna

- [Travelling wave antenna and V antenna](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Atravelling-wave-v-antenna) — Propagation and Antenna, chapter 3, asked 2×
- [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×
- [Single wire radiation and travelling wave long wire](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Asingle-wire-travelling-long-wire) — Propagation and Antenna, chapter 1

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