RF Field Guide ยท reviewed reference
Antenna patterns and downtilt
An antenna's gain is directional: the pattern determines where useful energy and unwanted energy go.
Question
How do pattern shape and downtilt change a service area and a backhaul link?
Inputs
- Horizontal and vertical pattern data
- Mount height, azimuth, mechanical/electrical tilt, and target geometry
Answer
Working
dBi is the peak gain relative to an isotropic radiator; it does not say the gain in every direction. Use a manufacturer pattern or a clearly labeled normalized/reconstructed model. Mechanical tilt rotates the whole pattern, while electrical tilt can change the vertical pattern behavior depending on the antenna design.
Visual explanation
- Pattern data
- Azimuth
- Elevation
- Tilt
- Target direction
- Off-axis gain
Interpretation
Choose an antenna and tilt from the geometry, not maximum peak gain alone. Verify side lobes, back lobes, polarization, mounting constraints, and the receive path as well as transmit coverage.