Horn Antenna
Understanding Horn Antennas
Horn antennas have been used since the earliest days of microwave engineering. Their appeal is simplicity, predictable gain, low VSWR, and broadband operation. A well-designed horn antenna provides gain that can be accurately calculated from its physical dimensions, making horns invaluable as gain reference standards.
Types of Horn Antennas
- Pyramidal horn: Flared in both E-plane and H-plane. The most common type. Used as gain standards because gain can be calculated from dimensions to within 0.1 dB.
- Sectoral horn (E-plane): Flared only in the E-plane. Produces a fan beam narrow in elevation and wide in azimuth.
- Sectoral horn (H-plane): Flared only in the H-plane. Produces a fan beam narrow in azimuth and wide in elevation.
- Conical horn: A circular waveguide flared into a cone. Produces a symmetric beam. Common as feeds for parabolic reflectors.
- Corrugated horn: Has circumferential grooves on the interior walls. Produces very low sidelobes, excellent pattern symmetry, and low cross-polarization. The preferred feed for high-performance reflector antennas.
- Scalar horn: A corrugated horn optimized for a specific flare angle that produces a frequency-independent beamwidth.
Gain Estimation
For a pyramidal horn with aperture dimensions A (H-plane) and B (E-plane), the approximate gain is: G = 10 log10(4 pi A B / lambda^2) - losses. Typical gains range from 10 dBi for small horns to 25+ dBi for large horns. Gain increases with aperture area and frequency.
G (dBi) = 10 × log10(4π × A_eff / λ²)
where A_eff = ε_ap × A_physical
ε_ap = aperture efficiency (typically 0.5 - 0.7)
For a standard gain horn:
G = 10log10(7.5 × a × b / λ²) dBi
(assumes 51% aperture efficiency)
Half-power beamwidth (approx):
θ = 70 × λ / D (degrees)
Horn Antenna Types Comparison
| Type | Gain Range | Sidelobes | Cross-Pol | Primary Use |
|---|---|---|---|---|
| Pyramidal | 10 - 25 dBi | -13 dB typ | -20 to -25 dB | Gain standards, general |
| Conical | 10 - 22 dBi | -15 dB typ | -20 to -30 dB | Reflector feeds |
| Corrugated | 12 - 25 dBi | -25 to -35 dB | -30 to -40 dB | High-perf feeds, radio astronomy |
| Lens-corrected | 20 - 35 dBi | -20 to -30 dB | -25 to -35 dB | Point-to-point links |
Frequently Asked Questions
What is a horn antenna used for?
Horn antennas are used as feeds for parabolic reflector antennas, as calibration standards for antenna gain measurements, and as standalone antennas for point-to-point microwave links. Their predictable performance, wide bandwidth, and simple construction make them one of the most versatile antenna types in microwave engineering.
How much gain does a horn antenna have?
Gain depends on operating frequency and aperture size. Small horns provide 10-15 dBi; standard gain horns for measurement provide 15-25 dBi; large lens-corrected horns can exceed 30 dBi. Gain increases with frequency at a fixed aperture size.
What is the bandwidth of a horn antenna?
Horn antennas are inherently broadband. A well-designed pyramidal horn operates across the entire single-mode bandwidth of its feeding waveguide, typically 40% fractional bandwidth. Ridged horns can achieve multi-octave bandwidth (e.g., 2-18 GHz from a single antenna).