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

# Antenna radiation pattern and lobes

Propagation and Antenna · Chapter 2: Antenna Parameters and Arrays

- Asked in: 2077 Chaitra, 2 marks; 2076 Baisakh, 2 marks; 2074 Bhadra, 2 marks; 2070 Magh, 2 marks (asked 4 times)
- Video: [Radiation pattern basics - HPBW, FNBW, Front to Back Ratio - EC 8701 - Antenna and Microwave Engg](https://www.youtube.com/watch?v=9x1k_-y8-Ps) — IV ECE CLASS
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/propagation_and_antenna/radiation-pattern
- Whole chapter: https://www.bctengineer.com/md/semester_6/propagation_and_antenna/chapter-2

## Question

Explain the radiation pattern (radiation pattern lobes) of an antenna.

## Short answer

Radiation pattern graphs far-field strength versus direction. Main lobe contains maximum radiation; minor lobes include side lobes adjacent and back lobe opposite. Nulls are zero-radiation directions. HPBW is angle between -3 dB points; FNBW between first nulls (≈2×HPBW). Side lobe level is side lobe peak relative to main lobe in dB.

## Answer

A **radiation pattern** is a graph (2-D or 3-D) of the radiated field strength or power of an antenna versus direction (θ, φ) in the far field. It is usually normalized to the maximum and drawn in the E-plane and H-plane.

Radiation pattern lobes:
- **Main (major) lobe:** lobe containing the direction of maximum radiation.
- **Minor lobes:** all other lobes; **side lobes** are next to the main lobe and the **back lobe** is opposite it.
- **Nulls:** directions of zero radiation between lobes.
- **HPBW:** angle between −3 dB points of the main lobe; **FNBW:** angle between first nulls.
- **Side lobe level:** side lobe peak relative to main lobe (dB).

```text
          main lobe
           .---.
          /     \  HPBW
   side  |       |  side
   lobe .|       |. lobe
       (  \  o  /  )
        '  '-+-'  '
           back lobe
```

## Check yourself

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

1. What is a radiation pattern?
   A. A graph of input impedance versus frequency
   B. A plot of VSWR
   C. A graph of radiated field or power versus direction in the far field
   D. A map of antenna currents
   Answer: C. It is a 2-D or 3-D plot, usually normalized, drawn in the E- and H-planes. (Key point: Definition)

2. Which defines the main lobe and back lobe?
   A. Main lobe contains the direction of maximum radiation; back lobe is opposite it
   B. Main lobe is the smallest lobe
   C. Back lobe is next to the main lobe
   D. Side lobes contain the maximum
   Answer: A. Minor lobes include side lobes next to the main lobe and the back lobe opposite it. (Key point: Lobes)

3. What do HPBW and FNBW measure?
   A. HPBW is between first nulls; FNBW is between -3 dB points
   B. HPBW is between -3 dB points; FNBW is between first nulls
   C. Both are between -10 dB points
   D. Both are side lobe levels
   Answer: B. HPBW is the angle between half-power (-3 dB) points; FNBW is the angle between the first nulls. (Key point: Beamwidth terms)

## Related in Propagation and Antenna

- [Pattern lobes and 180° out-of-phase array](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Alobes-importance-opposite-phase-array) — Propagation and Antenna, chapter 2
- [Radiation pattern, gain and power flux density](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Apattern-gain-power-flux-density) — Propagation and Antenna, chapter 2
- [Antenna definition and single wire radiation conditions](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Asingle-wire-radiation-conditions) — Propagation and Antenna, chapter 1, asked 4×
- [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
- [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×
- [Types of wired antenna](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Awired-antenna-types) — Propagation and Antenna, chapter 3