What is the relationship between antenna size and beamwidth at millimeter wave frequencies?
mmWave Antenna Beamwidth
The relationship θ3dB ≈ k × λ/D (where k is a constant depending on the aperture illumination, typically 58-70) is a universal principle of diffraction-limited apertures. It applies equally to optical telescopes, radar antennas, and mmWave communications antennas. At mmWave frequencies, the small wavelength means that physically small apertures achieve the same beamwidth and gain that would require much larger apertures at microwave frequencies.
| Parameter | Low Gain | Medium Gain | High Gain |
|---|---|---|---|
| Gain Range | 2-6 dBi | 6-15 dBi | 15-45 dBi |
| Beamwidth | 60-360° | 15-60° | 1-15° |
| Typical Types | Dipole, monopole, patch | Yagi, helical, horn | Parabolic, array, Cassegrain |
| Bandwidth | Narrow to wide | Moderate | Narrow to moderate |
| Complexity | Low | Medium | High |
Frequently Asked Questions
How does this affect 5G mmWave?
5G mmWave systems at 28 and 39 GHz use antenna arrays with 64-256 elements to achieve both high gain (beam reach) and electronic beam steering (track moving users). The array aperture is 50-100 mm, producing beamwidths of 5-15°. Multiple beams are formed simultaneously to serve multiple users.
What pointing accuracy is needed?
For reliable communication: pointing error should be less than θ3dB/3 ≈ 0.2× beamwidth. For a 3° beam: pointing accuracy must be better than ±1°. For a 1° beam (large dish): pointing accuracy must be better than ±0.3°. This requires precision positioners or electronic steering.
Can I use a wider beam at mmWave?
Yes, by using a smaller antenna. But a wider beam has lower gain, reducing the link range. The design trades off coverage area (beam width) against link distance (gain). Sector antennas with 30-90° beamwidth are used for short-range mmWave coverage with moderate gain.