Antenna downtilt calculator
Downtilt is the angle a sector antenna is aimed below horizontal so its main beam lands on the intended coverage ring instead of the horizon. The angle follows from the height difference and the distance, θ = atan(Δh/d), plus a small earth-curvature term. This calculator also shows where the −3 dB beam edges reach the ground.
Height of the antenna centre above local ground.
From the antenna datasheet: 6–8° for a typical high-gain macro panel.
Top: the angle at the antenna, drawn on a magnified scale — the dashed horizontal, the tick scale in degrees, and the green sector spanning the −3 dB beam with its centre ray. Bottom: where those two edges land on the ground, on a plain linear distance scale from the antenna; the shaded stretch is what the −3 dB beam covers.
Footprint edges use a flat-earth ray, with curvature applied to the aim angle only. Real coverage follows terrain, clutter and the antenna’s actual vertical pattern, including its sidelobes.
How it works
- 01
Aim the beam centre
The geometric aim is θ = atan(Δh / d), where Δh is the antenna centre minus the target height. The earth-curvature term d / (2·k·R) rides on top of it: 0.007° at 2 km, 0.10° at 30 km, so it only shows up on long rural cells and microwave hops. The angles are small: a 30 m mast serving a ring 2 km out needs just 0.82°.
- 02
Know your beamwidth
A panel antenna radiates a vertical fan, not a ray. The −3 dB (half-power) beamwidth spans that fan: a 7° panel puts its edges at θ ± 3.5°, a 14° panel at θ ± 7°. Gain and beamwidth trade off against each other. An 18 dBi macro panel is typically 6–8° in the vertical plane.
- 03
Find the footprint on the ground
Each edge ray lands where d = Δh / tan(angle). The lower edge sets the inner limit of the −3 dB footprint, the upper edge the outer limit. If the upper edge points at or above horizontal, which happens whenever θ < BW/2, it never lands and half the beam spills past the cell.
- 04
Tilt for containment, not just for aim
Operators usually tilt further than the geometric aim, putting the upper −3 dB edge near the cell boundary so energy stays inside the cell. Typical macro-cell values are 2–10°. Overshoot beyond the boundary is interference to the next cell, and in dense networks it costs more capacity than it adds coverage.
Formulas
- θ — downtilt below horizontal, degrees
- Δh — antenna centre height minus target height, m
- d — ground distance to the target, m
- k — effective-earth-radius factor, 4/3 in a standard atmosphere
- R — Earth radius, 6 371 000 m, so 2·k·R = 16 989 333 m
- BW — vertical −3 dB beamwidth, degrees
- θ + BW/2 — lower edge, gives the inner footprint limit
- θ − BW/2 — upper edge, gives the outer limit. ≤ 0 means it never lands
Worked example
- Δh = 30 − 1.5 = 28.5 m
- 2·k·R = 2 · (4/3) · 6 371 000 = 16 989 333 m
- θ = atan(28.5/2000 + 2000/16 989 333) = 0.82°
- lower edge: 0.82 + 3.5 = 4.32° → 28.5 / tan(4.32°) = 377 m
- upper edge: 0.82 − 3.5 = −2.68° → above horizontal, never lands
- → under 1° of tilt most of a 7° beam flies over the target, so tilt more or accept the overshoot
FAQ
- What is the difference between mechanical and electrical downtilt?
- Mechanical downtilt physically tips the antenna, so the beam drops in the pointing direction but rises again toward the sides, warping the horizontal pattern. Electrical downtilt shifts the phase across the radiating elements, tilting the whole pattern uniformly in every azimuth. Most macro panels combine a few degrees of each.
- Why downtilt an antenna at all?
- To keep energy inside the intended cell. An untilted panel sends its main beam at the horizon, where it serves nobody and interferes with distant cells reusing the same channel. Tilting also fills in coverage close to the mast, under the main beam.
- How much downtilt is typical?
- Between 2° and 10° for macro cells, and more for rooftop and small-cell sites. The pure geometric aim is usually far smaller: a 30 m mast over 2 km gives atan(28.5 / 2000) = 0.82°. In practice the tilt is therefore set by beamwidth and containment, not by pointing at a single target.
- What happens with too much downtilt?
- The footprint pulls in toward the mast and the cell edge starves. Users at the boundary end up served by sidelobes typically 15–20 dB below the main beam, so throughput collapses and handovers get erratic. The usable radius then shrinks faster than the geometry suggests, because the vertical pattern rolls off steeply past the −3 dB edge.
Tilt set? Now see the footprint it actually produces. Waveshed drapes your antenna pattern over real elevation data and draws the coverage, free in your browser.
Simulate the sector →Related guides
- Antenna patterns & the sensor panel — build the vertical pattern the tilt is applied to and read it as a polar plot
- Heights: AGL vs AMSL — Δh is only right when both heights use the same reference
Sources & further reading
- Beam tilt — Wikipedia ↗ — mechanical vs electrical tilt and how cellular networks use them
- ITU-R Recommendation P.530 — Propagation data for terrestrial line-of-sight systems ↗ — source of the effective-earth-radius factor k in the curvature term
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