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

# List and explain antenna parameters

Propagation and Antenna · Chapter 2: Antenna Parameters and Arrays

- Asked in: 2073 Magh, 2+6 marks
- Video: [ANTENNA PARAMETERS PART 1](https://www.youtube.com/watch?v=EW_w82X-tTw) — Prof. Barapate's Tutorials
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/propagation_and_antenna/list-antenna-parameters
- Whole chapter: https://www.bctengineer.com/md/semester_6/propagation_and_antenna/chapter-2

## Question

List the parameters of antenna and explain any three of them.

## Short answer

Antenna parameters include radiation pattern, directivity, gain, efficiency, beamwidth, bandwidth, input impedance, radiation resistance, polarization, effective aperture, side lobe level and EIRP. Directivity is D = 4πU_max/P_rad, gain is G = ηD, and HPBW is the half-power angle, for example 90° for a short dipole.

## Answer

Antenna parameters are the quantities used to describe the performance of an antenna.

#### List of antenna parameters
1. Radiation pattern
2. Directivity
3. Gain
4. Radiation efficiency
5. Beamwidth (HPBW, FNBW)
6. Bandwidth
7. Input impedance
8. Radiation resistance
9. Polarization
10. Effective aperture (effective area)
11. Front-to-back ratio, side lobe level
12. EIRP

#### Explanation of three parameters

**1. Directivity**

```text
D = U_max / U_avg = 4π U_max / P_rad
```

It is the ratio of the maximum radiation intensity to the average intensity. For a short dipole U = U0 sin²θ, P_rad = 8πU0/3, so D = 1.5 (1.76 dBi). For narrow beams D ≈ 41253/(θ1° θ2°). Isotropic D = 1; λ/2 dipole 1.64.

**2. Gain**

```text
G = 4π U_max / P_in = η D
```

Gain includes losses, so G ≤ D. Expressed in dBi; dBi = dBd + 2.15. Also G = 4πAe/λ² for aperture antennas. Example: a 1.2 m dish at 12 GHz with 55 % efficiency has G ≈ 41.0 dBi.

**3. Half power beamwidth (HPBW)**
The angle between the two directions of the main lobe where power is half (−3 dB) of maximum. For a short dipole, sin²θ = 0.5 gives θ = 45° and 135°, so HPBW = 90°; λ/2 dipole ≈ 78°.

```text
        max
       .---.
 0.707/  |  \0.707
     /<HPBW>\
    /         \
```

A narrow beamwidth means high directivity and better rejection of interference from other directions.

## Check yourself

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

1. What is the directivity of a short dipole?
   A. 1.5 (1.76 dBi)
   B. 1.64 (2.15 dBi)
   C. 1 (0 dBi)
   D. 3 (4.8 dBi)
   Answer: A. D = 4πU0/(8πU0/3) = 1.5. (Key point: Directivity)

2. How is gain related to directivity?
   A. G = D/η
   B. G = ηD, so G <= D
   C. G = D + η
   D. G >= D
   Answer: B. Gain includes losses. (Key point: Gain vs directivity)

3. What is the HPBW of a short dipole?
   A. 45°
   B. 78°
   C. 90°
   D. 135°
   Answer: C. sin²θ = 0.5 gives 45° and 135°. (Key point: HPBW)

4. What does a narrow beamwidth imply?
   A. Lower directivity
   B. A larger side lobe angle
   C. Higher radiation resistance
   D. Higher directivity and better rejection of interference from other directions
   Answer: D. A narrower beam concentrates power. (Key point: Narrow beam)

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- [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

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