---
title: "Importance of arrays; end fire vs broadside"
subject: "Propagation and Antenna"
chapter: 2
key: "semester_6/propagation_and_antenna:array-importance-endfire-broadside"
source: https://www.bctengineer.com/q/semester_6/propagation_and_antenna/array-importance-endfire-broadside
site: BCT Engineering
---

# Importance of arrays; end fire vs broadside

Propagation and Antenna · Chapter 2: Antenna Parameters and Arrays

- Asked in: 2077 Chaitra, 2+6 marks; 2076 Baisakh, 2+6 marks (asked 2 times)
- Video: [Antenna Array (Basics, Linear Antenna Array, Planner Antenna Array, Electric Field & Array Factor)](https://www.youtube.com/watch?v=OgNnrNMaLC0) — Engineering Funda
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/propagation_and_antenna/array-importance-endfire-broadside
- Whole chapter: https://www.bctengineer.com/md/semester_6/propagation_and_antenna/chapter-2

## Question

What is the importance of antenna array? Describe the principle of End fire and Broadside array, and differentiate between them.

## Short answer

Antenna arrays provide high directivity, beam steering, and power sharing. A broadside array has all elements in phase (δ=0) radiating perpendicular to the axis. An end-fire array has progressive phase δ = -βd, radiating along the axis. End-fire gives higher directivity (~4Nd/λ) than broadside (~2Nd/λ).

## Answer

An **antenna array** is a group of similar antennas arranged in a regular geometry and fed with controlled amplitudes and phases so that their fields add in the desired directions.

#### Importance of antenna array
- Gives **high directivity and gain** that one small element cannot give.
- **Narrow, steerable beam**: the beam direction can be changed electronically by changing the phase (phased arrays, radar).
- The pattern can be **shaped**: low side lobes, nulls towards interference.
- Higher **total power handling**, since the power is shared by many elements.
- Better reliability: failure of one element does not stop operation.

For a uniform linear array of N elements, spacing d, progressive phase δ:

```text
ψ = βd cosθ + δ
AF = sin(Nψ/2) / [N sin(ψ/2)]
Maximum when ψ = 0
```

#### Broadside array
- All elements are fed **in phase** (δ = 0).
- ψ = 0 at θ = 90°, so maximum radiation is **perpendicular to the array axis**.
- The pattern is a disk-like beam around the axis (narrow in the plane containing the axis).

#### End-fire array
- Progressive phase **δ = −βd**, i.e. each element lags the previous one by the phase delay over spacing d.
- ψ = βd(cosθ − 1) = 0 at θ = 0°, so maximum radiation is **along the array axis**.

```text
 Broadside                End-fire
      ^ ^ ^ ^                 
      | | | |             o o o o o  ====>
   o--o--o--o--o          max along axis
   max perpendicular
```

#### Difference

| Point | Broadside | End-fire |
|---|---|---|
| Phase shift δ | 0 (in phase) | −βd (progressive) |
| Max direction | ⊥ to array axis (θ = 90°) | Along axis (θ = 0°) |
| Pattern | Fan/disk shaped | Cigar/pencil along axis |
| BWFN | ≈ 2λ/(Nd) | ≈ 2√(2λ/(Nd)) |
| Directivity | ≈ 2Nd/λ | ≈ 4Nd/λ |
| Example N = 10, d = λ/4 | BWFN ≈ 46°, D ≈ 5 | BWFN ≈ 103°, D ≈ 10 |
| Typical use | Broadcast, base stations | Yagi-Uda, log-periodic, point-to-point |

The end-fire spacing is kept below λ/2: with d = λ/2 and δ = −βd, a second equal main lobe appears at θ = 180°, and the directivity drops to about that of a broadside array.

## Check yourself

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

1. Which is a key reason for using an antenna array?
   A. It lets a single element radiate with no phase control
   B. It gives a high-gain, narrow beam that can be shaped and electronically steered by changing phase
   C. It removes the need for any feed system
   D. It makes the pattern omnidirectional
   Answer: B. Controlled amplitudes and phases give directivity, steering, side-lobe control and nulls. (Key point: Importance of arrays)

2. What feeding condition gives a broadside array and where is its maximum?
   A. All elements in phase (δ = 0); maximum perpendicular to the array axis
   B. Progressive phase δ = -βd; maximum along the axis
   C. All elements 180° out of phase; maximum perpendicular to the axis
   D. Progressive phase δ = +90°; maximum at 45°
   Answer: A. With δ = 0, ψ = βd cosθ is zero at θ = 90°. (Key point: Broadside condition)

3. What progressive phase makes a uniform linear array end-fire?
   A. δ = 0
   B. δ = +βd/2
   C. δ = -βd, so ψ = βd(cosθ - 1) = 0 at θ = 0°
   D. δ = π for all elements
   Answer: C. The phase lag cancels the path delay along the axis, so the maximum is along the axis. (Key point: End-fire condition)

4. Which statement correctly compares the two for the same N and d?
   A. Broadside has higher directivity and a narrower beam
   B. Both have identical directivity
   C. End-fire is used for base station broadcast, broadside for Yagi antennas
   D. End-fire has about twice the directivity (about 4Nd/λ vs 2Nd/λ) but a wider beam than broadside
   Answer: D. For N = 10, d = λ/2 the answer gives D about 20 for end-fire and about 10 for broadside. (Key point: Broadside vs end-fire)

## Related in Propagation and Antenna

- [Linear array; broadside vs end fire](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Alinear-array-broadside-endfire) — Propagation and Antenna, chapter 2
- [Two-element array: broadside and end fire](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Atwo-element-array-broadside-endfire) — Propagation and Antenna, chapter 2
- [Two-element array and end fire pattern](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Atwo-isotropic-endfire-pattern) — Propagation and Antenna, chapter 2
- [Features of end-fire array](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Aendfire-array-features) — Propagation and Antenna, chapter 2
- [Short note: Broadside vs endfire array](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Abroadside-endfire-short-note) — Propagation and Antenna, chapter 2
- [Antenna arrays and two-element expression](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Adefine-array-two-isotropic) — Propagation and Antenna, chapter 2

## Related in other subjects

- [Array overflow/underflow; add two arrays](https://www.bctengineer.com/question.md?key=semester_1%2Fcomputer_programming%3Aarray-overflow-underflow-add) — Computer Programming, chapter 7