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

# Linear array; broadside vs end fire

Propagation and Antenna · Chapter 2: Antenna Parameters and Arrays

- Asked in: 2073 Bhadra, 1+4 marks
- Video: [Types of Antenna Array - Broadside array, End-fire array, collinear array](https://www.youtube.com/watch?v=95MfBLjrHsU) — Padmasri Naban
- 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-array-broadside-endfire
- Whole chapter: https://www.bctengineer.com/md/semester_6/propagation_and_antenna/chapter-2

## Question

What is a linear array? Differentiate between a broadside array and end fire array.

## Short answer

Linear array has elements placed along a straight line with uniform spacing and progressive phase shift. Broadside array: α=0, maximum radiation perpendicular to axis (θ=90°), bidirectional, typical spacing λ/2, directivity ≈2L/λ. End-fire array: α=-βd, maximum along axis (θ=0° or 180°), usually unidirectional, spacing λ/4, directivity ≈4L/λ.

## Answer

A **linear array** is an array whose elements are placed along a straight line (the array axis), usually equally spaced, equal in amplitude and with a uniform progressive phase shift α between neighbours. Its array factor is

```text
AF = sin(nψ/2) / [n sin(ψ/2)],  ψ = βd cosθ + α
```

#### Broadside vs end fire array

| Point | Broadside array | End fire array |
|---|---|---|
| Direction of max | Perpendicular to array axis (θ = 90°) | Along array axis (θ = 0° or 180°) |
| Phase condition | α = 0 (all in phase) | α = −βd (progressive phase) |
| Pattern | Bidirectional fan/disc around axis | Usually unidirectional pencil along axis |
| Null-to-null beamwidth | ≈ 2λ/(nd) | ≈ 2√(2λ/(nd)) |
| Directivity (long array) | ≈ 2L/λ | ≈ 4L/λ |
| Typical spacing | λ/2 | λ/4 |
| Example | Collinear/curtain arrays for HF broadcast | Yagi-Uda, end-fire HF arrays |

```text
 Broadside:             End fire:
      ^  max                 
      |                 
  o o o o o  axis       o o o o o ===> max
      |                  along axis
      v  max
```

Broadside arrays give a beam at right angles to the line of elements, so they suit point-to-point links where the array can be mounted across the direction of transmission. End fire arrays give higher directivity for the same length and are used where the line of elements can point at the target.

## Check yourself

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

1. Which describes a linear array as in the answer?
   A. Elements placed along a straight line, usually equally spaced, with uniform progressive phase shift
   B. Elements placed around a circle with random phases
   C. Elements placed on a plane with unequal amplitudes only
   D. A single element fed through a reflector
   Answer: A. A linear array has its elements on a straight line (the array axis), normally equally spaced and with a progressive phase shift alpha. (Key point: Linear array definition)

2. What phase condition gives a broadside array?
   A. alpha = -beta d
   B. alpha = 0, all elements in phase
   C. alpha = 90° for every neighbour
   D. alpha = pi/n
   Answer: B. With all currents in phase, psi = 0 at theta = 90°, so the maximum is normal to the array axis. (Key point: Broadside phase condition)

3. For an end fire array, the progressive phase shift is
   A. alpha = 0
   B. alpha = +2 beta d
   C. alpha = -beta d
   D. alpha = beta d cos(theta)
   Answer: C. alpha = -beta d makes psi = beta d (cos theta - 1) = 0 along the axis (theta = 0°), so the beam lies along the array line. (Key point: End fire phase condition)

4. For a long array of the same length L, which statement is correct?
   A. Broadside directivity is about twice end fire
   B. Both have the same directivity 2L/lambda
   C. End fire directivity is about 10 times broadside
   D. End fire directivity (~4L/lambda) is about twice broadside (~2L/lambda)
   Answer: D. The table gives D of about 2L/lambda for broadside and about 4L/lambda for end fire. (Key point: Directivity comparison)

## Related in Propagation and Antenna

- [Importance of arrays; end fire vs broadside](https://www.bctengineer.com/question.md?key=semester_6%2Fpropagation_and_antenna%3Aarray-importance-endfire-broadside) — Propagation and Antenna, chapter 2, asked 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

## Related in other subjects

- [Linear queue using array](https://www.bctengineer.com/question.md?key=semester_4%2Fdata_structure_and_algorithm%3Alinear-queue-array-implementation) — Data Structure and Algorithm, chapter 2, asked 2×