What is a corrugated horn antenna and why does it use a corrugated waveguide feed?
Corrugated Horn Design Principles
A smooth-walled horn antenna supports the TE11 mode, which has an inherently asymmetric radiation pattern: the E-plane pattern is narrower than the H-plane pattern, and the cross-polarization is relatively high (-15 to -20 dB). This asymmetry reduces the aperture efficiency when used as a parabolic reflector feed because the unsymmetric illumination wastes part of the reflector area.
| Parameter | Standard Rect. | Ridged | Circular |
|---|---|---|---|
| Single-Mode BW | 40% (1.25-1.9 fc) | 50-150% | 26% (1.31:1 ratio) |
| Attenuation | Low | Moderate (3-5x) | Low to very low |
| Power Handling | High (kW-class) | Moderate | High |
| Polarization | Single | Single | Dual (TE11) |
| Cost | Low (commodity) | Medium | High (specialty) |
Frequently Asked Questions
What bandwidth does a corrugated horn provide?
Standard corrugated horns with uniform corrugation depth provide about 1.4:1 bandwidth (matching the circular waveguide single-mode range). Wideband designs using variable-depth corrugations and profiled flares achieve 1.6:1 to 2:1 bandwidth. Ultra-wideband designs exist but sacrifice pattern symmetry at the band edges.
How many corrugations per wavelength?
Typically 3-5 corrugations per wavelength. The corrugation period must be much smaller than the wavelength to act as an effective surface impedance rather than a diffraction grating. At X-band (10 GHz), corrugation spacing is approximately 3-5 mm. At W-band (94 GHz), it is 0.3-0.5 mm, requiring precision machining or electroforming.
Is a corrugated horn always better?
For reflector antenna feeds: almost always yes, due to superior pattern symmetry and low cross-polarization. For direct radiators where pattern symmetry is less critical: smooth-walled horns are simpler, cheaper, and lighter. For very wide bandwidth requirements (multi-octave): a ridged horn may be preferred despite its inferior pattern symmetry.