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

# Short note: Linear polarization

Propagation and Antenna · Chapter 2: Antenna Parameters and Arrays

- Asked in: 2072 Magh, 3 marks
- Video: [Linear Polarization Explained | EM Waves & Antenna Basics](https://www.youtube.com/watch?v=KIWkCGLRqHA) — WaveRes
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/propagation_and_antenna/linear-polarization-short-note
- Whole chapter: https://www.bctengineer.com/md/semester_6/propagation_and_antenna/chapter-2

## Question

Write a short note on linear polarization.

## Short answer

Linear polarization occurs when the tip of the electric field vector at a fixed point moves along a straight line. This happens when only one component exists or two orthogonal components are in phase or 180° out of phase. Types are vertical, horizontal and slant; PLF = cos²ψ, giving zero for cross-polarization.

## Answer

An antenna or wave is **linearly polarized** when the tip of its electric field vector, at a fixed point, always moves along a **straight line** as time passes.

Conditions (with components Ex, Ey):
- Only one component exists, or
- Two orthogonal components are **in phase or 180° out of phase** (Δφ = nπ), with any amplitudes.

```text
  Vertical   Horizontal   Slant (45°)
     |                       /
     |        -------       /
     |                     /
```

Types:
- **Vertical polarization:** E perpendicular to the earth, e.g. vertical monopole, AM/mobile.
- **Horizontal polarization:** E parallel to the earth, e.g. horizontal dipole, TV broadcast.
- **Slant (±45°):** used for polarization diversity in cellular base stations.

Axial ratio = ∞. A linearly polarized receiving antenna gets PLF = cos²ψ, where ψ is the angle between wave and antenna polarizations; cross-polarized (ψ = 90°) reception gives zero signal. A linear antenna receives half of the power (3 dB loss) of a circularly polarized wave.

## Check yourself

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

1. What defines a linearly polarized wave?
   A. The tip of the E vector moves along a straight line at a fixed point
   B. The tip traces a circle
   C. The tip traces an ellipse
   D. The E vector rotates with the frequency of the carrier only
   Answer: A. Linear polarization has a straight-line trace of E. (Key point: Definition)

2. When do two orthogonal components Ex and Ey give linear polarization?
   A. Only when they have equal amplitudes and are 90° apart
   B. When they are in phase or 180° out of phase (Δφ = nπ), with any amplitudes
   C. Only when their amplitudes are equal and Δφ = 0
   D. Whenever Δφ is not zero
   Answer: B. Δφ = nπ keeps the resultant along a fixed line. (Key point: Condition for two components)

3. What is the PLF of a linear receiving antenna whose polarization is 90° to the wave (cross-polarized)?
   A. 1
   B. 0.5
   C. Zero, since PLF = cos²ψ
   D. 0.707
   Answer: C. cos²(90°) = 0, so no signal is received. (Key point: Polarization loss)