What is the sidelobe level of an antenna and why does it matter for interference rejection?
Sidelobe Performance
Sidelobes create three problems: (1) they receive interference from directions other than the intended signal (degrading SNR), (2) they transmit energy in unintended directions (potentially violating emission regulations), and (3) in radar, they create false targets from clutter and jammers outside the main beam.
| 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
What if my antenna exceeds the sidelobe envelope?
The antenna may cause harmful interference to adjacent satellite systems and will not be approved for operation. Redesign the feed or reflector to reduce sidelobes (increase edge taper, improve feed pattern, reduce strut blockage) until the envelope is met.
How do I achieve -40 dB sidelobes?
Use a Taylor or Dolph-Chebyshev amplitude distribution across the aperture. For arrays, this means applying specific amplitude weights to each element. For reflectors, it requires a feed pattern with very low edge illumination (-25 to -30 dB taper), which reduces gain by 2-3 dB.
Do beam steering affect sidelobes?
Yes. When a phased array scans off boresight, the element pattern modifies the sidelobe structure. Near wide scan angles, grating lobes can appear if the element spacing exceeds λ/2. Additionally, the beamwidth broadens as 1/cosθs, changing the sidelobe positions relative to the main beam.