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

# Any five antenna parameters

Propagation and Antenna · Chapter 2: Antenna Parameters and Arrays

- Asked in: 2071 Bhadra, 5 marks
- Video: [2 Introduction to Antennas Basics & Parameters Explained Module 3 | 7th Sem ECE VTU](https://www.youtube.com/watch?v=2Vd3edHwqVk) — VTU Academy
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/propagation_and_antenna/five-antenna-parameters
- Whole chapter: https://www.bctengineer.com/md/semester_6/propagation_and_antenna/chapter-2

## Question

Explain any five parameters of antenna.

## Short answer

Radiation pattern: graph of radiated field vs direction. Directivity: ratio of max radiation intensity to average (e.g., λ/2 dipole 1.64, 2.15 dBi). Gain: directivity including losses. Radiation efficiency: radiated power over input power. Half-power beamwidth: angle between −3 dB points (λ/2 dipole 78°).

## Answer

Antenna parameters describe how well an antenna radiates or receives. Five important ones:

1. **Radiation pattern:** a graph of the radiated field or power versus direction (θ, φ) in the far field. It shows the main lobe, side lobes, back lobe and nulls. E.g. short dipole: E ∝ sinθ (doughnut).

2. **Directivity (D):** ratio of maximum radiation intensity to average radiation intensity:

```text
D = 4π U_max / P_rad
```

   Short dipole 1.5; λ/2 dipole 1.64 (2.15 dBi).

3. **Gain (G):** directivity including losses: G = ηD = 4πU_max/P_in. Expressed in dBi.

4. **Radiation efficiency (η):**

```text
η = P_rad / P_in = Rr / (Rr + RL)
```

   e.g. Rr = 73 Ω, RL = 2 Ω → 97.3 %.

5. **Half power beamwidth (HPBW):** angle between the −3 dB points of the main lobe; short dipole 90°, λ/2 dipole 78°. Narrow beam → high directivity.

Other parameters: bandwidth, input impedance, polarization, effective aperture.

## Check yourself

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

1. What is the E-field pattern of a short dipole?
   A. E ∝ sinθ (doughnut)
   B. E ∝ cosθ
   C. E ∝ sin²θ
   D. Uniform in all directions
   Answer: A. Power ∝ sin²θ. (Key point: Short dipole pattern)

2. Directivity is
   A. 4πU_max/P_in
   B. 4πU_max/P_rad
   C. P_rad/U_max
   D. U_avg/U_max
   Answer: B. It is a ratio of maximum to average intensity. (Key point: Directivity)

3. Rr = 73 Ω, RL = 2 Ω gives η =
   A. 2.7 %
   B. 50 %
   C. 97.3 %
   D. 73 %
   Answer: C. η = 73/75. (Key point: Efficiency)

4. What are the HPBW values of the short dipole and the λ/2 dipole?
   A. 90° and 78°
   B. 78° and 90°
   C. 45° and 51°
   D. 180° and 90°
   Answer: A. The longer dipole has a slightly narrower beam. (Key point: HPBW)

## Related in Propagation and Antenna

- [List and explain antenna parameters](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Alist-antenna-parameters) — Propagation and Antenna, chapter 2
- [Infinitesimal dipole fields and basic parameters](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Ainfinitesimal-dipole-fields-parameters) — Propagation and Antenna, chapter 1
- [Five-element Yagi design for 100 MHz](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Ayagi-design-100mhz) — Propagation and Antenna, chapter 3, asked 2×

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