---
title: "Antenna polarization"
subject: "Propagation and Antenna"
chapter: 2
key: "semester_6/propagation_and_antenna:polarization"
source: https://www.bctengineer.com/q/semester_6/propagation_and_antenna/polarization
site: BCT Engineering
---

# Antenna polarization

Propagation and Antenna · Chapter 2: Antenna Parameters and Arrays

- Asked in: 2081 Chaitra, 3 marks; 2080 Chaitra, 3 marks; 2079 Chaitra, 3 marks; 2077 Chaitra, 2 marks; 2075 Bhadra, 3 marks; 2074 Bhadra, 2 marks; 2070 Magh, 2 marks; 2069 Bhadra, 2 marks (asked 8 times)
- Video: [Radio Waves and Signal Polarisation HF, VHF and UHF](https://www.youtube.com/watch?v=lQfaH_fl1R4) — DXCommander
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/propagation_and_antenna/polarization
- Whole chapter: https://www.bctengineer.com/md/semester_6/propagation_and_antenna/chapter-2

## Question

Explain the polarization of an antenna.

## Short answer

Polarization is the figure traced by the electric field vector tip in the far field. Linear: E moves along a line (single component or in-phase components). Circular: equal amplitude orthogonal components with 90° phase difference, rotating E. Elliptical: general case with unequal amplitude and/or phase difference. Axial ratio = major/minor axis; polarization loss factor = cos²ψ.

## Answer

**Polarization** of an antenna is the polarization of the wave it radiates in a given direction (usually the direction of maximum gain): the figure traced by the tip of the **electric field vector** with time at a fixed point in the far field.

Types:
- **Linear:** E moves along a straight line. Occurs when there is one component, or two components in phase (or 180° apart). Vertical (e.g. vertical monopole) or horizontal (e.g. horizontal dipole).
- **Circular:** E rotates with constant magnitude. Needs two orthogonal components of **equal amplitude** and **90° phase difference**. Right-hand (RHCP) or left-hand (LHCP), e.g. axial-mode helix.
- **Elliptical:** general case; two orthogonal components with unequal amplitude and/or a phase difference other than 0° or 180°.

```text
  Linear     Circular     Elliptical
    |          .-.          .--.
    |         (   )        (    )
    |          '-'          '--'
```

**Axial ratio** AR = major axis / minor axis: 1 for circular, ∞ for linear.

**Polarization loss factor:** PLF = cos²ψ, where ψ is the angle between the wave and antenna polarizations. A vertical antenna receiving a horizontal wave gets PLF = 0 (no signal).

## Check yourself

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

1. What does the polarization of an antenna describe?
   A. The figure traced by the tip of the E-field vector with time in the far field, in a given direction
   B. The direction of power flow
   C. The magnetic dipole moment
   D. The beamwidth
   Answer: A. Polarization is the shape traced by E at a fixed point, usually in the direction of maximum gain. (Key point: Definition)

2. What is needed for circular polarization?
   A. Two in-phase components
   B. Two orthogonal components of equal amplitude and 90° phase difference
   C. A single component
   D. Two components of unequal amplitude
   Answer: B. Equal amplitude and 90° phase give constant-magnitude rotation of E. (Key point: Condition for circular polarization)

3. What is the axial ratio for circular and linear polarization?
   A. Infinity for circular, 1 for linear
   B. 1 for both
   C. 0 for circular, 1 for linear
   D. 1 for circular, infinity for linear
   Answer: D. AR = major/minor axis: 1 for circular, infinite for linear. (Key point: Axial ratio)

4. A vertical antenna receives a horizontally polarized wave. What is the PLF?
   A. 1
   B. 0.5
   C. 0, since PLF = cos²ψ with ψ = 90°
   D. 2
   Answer: C. PLF = cos²ψ; with ψ = 90° no signal is received. (Key point: Polarization loss factor)

## Related in Propagation and Antenna

- [Short note: Linear polarization](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Alinear-polarization-short-note) — Propagation and Antenna, chapter 2
- [Gain, efficiency and polarization](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Again-efficiency-polarization) — Propagation and Antenna, chapter 2
- [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
- [Types of wired antenna](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Awired-antenna-types) — Propagation and Antenna, chapter 3