- 2075 Baisakh · 4 marks
Short note: Broadside vs endfire array
Short answer
Both are uniform linear arrays differing only in progressive phase α. Broadside: α=0, beam at θ=90° normal to axis, bidirectional disc pattern, spacing λ/2, directivity ≈2L/λ. End-fire: α=-βd, beam along axis θ=0°, mostly unidirectional pencil beam, spacing λ/4, directivity ≈4L/λ (Hansen-Woodyard ≈7.2L/λ).
Write a short note comparing broadside array and endfire array.
A broadside array and an end fire array are both uniform linear arrays (equal amplitude, equal spacing d). They differ only in the progressive current phase α, which decides where the beam points. The array factor is AF = sin(nψ/2)/[n sin(ψ/2)], ψ = βd cosθ + α, with maximum where ψ = 0.
Broadside (α = 0) End fire (α = -βd)
↑ beam
● ● ● ● ● ← axis ● ● ● ● ● ⇒ beam
↓ beam along the axis
| Feature | Broadside | End fire |
|---|---|---|
| Phase shift α | 0 (all in phase) | −βd |
| Beam direction | θ = 90°, normal to axis | θ = 0°, along axis |
| Pattern | Bidirectional; disc around axis | Mostly unidirectional |
| Usual spacing | λ/2 | λ/4 |
| FNBW | 2λ/(nd) | 2√(2λ/(nd)) |
| Directivity | ≈ 2L/λ | ≈ 4L/λ (Hansen-Woodyard ≈ 7.2L/λ) |
| Examples | Collinear, curtain arrays | Yagi-Uda, helical (axial mode) |
Key points:
- For the same length L = nd, the end fire beam is broader in angle terms but its directivity is about twice that of broadside.
- Broadside arrays are used for HF broadcasting and fixed links; end fire arrays for TV reception and point-to-point VHF/UHF links.
✓ Answer checked by Claude Opus 5.5 (high effort)
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