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Using the Antenna Downtilt Calculator

What this page is for

Estimating where an antenna’s vertical beam meets a receiver-height plane, or what tilt places the beam at a chosen distance. It answers a geometry question for one vertical cut through the pattern; it is not a coverage prediction.

Before you start

  • Have the antenna’s radiation-centre height above its ground and the receiver height above the target ground.
  • Have the half-power (−3 dB) vertical beamwidth from the datasheet for the vertical cut you are aiming along. The calculator does not fill this from the catalogue.
  • Keep the site and target ground elevations on the same vertical datum when you open Ground elevations.

Steps

  1. Choose Metric or Imperial under Units. Switching units converts what you typed; it does not change the stored physical values.
  2. Choose I know the tilt — where does the beam land? to enter a tilt, or I know the distance — what tilt? to work backwards from a target distance.
  3. Enter Antenna height above ground, Receiver height above its ground and Vertical beamwidth, half-power (−3 dB). The antenna height is the radiation centre, not the top of the mast.
  4. In distance mode, enter Target distance and choose whether to place the beam centre or the near half-power edge there. The near edge is where the half-power band begins.
  5. Choose Electrical or Mechanical under Tilt type. Mechanical tilt is shown for the boresight direction; the plan view shows how it differs around the antenna.
  6. Use Beam view for the local footprint or Horizon view to see the full line-of-sight range. Select a ray to inspect its angle, distance and state.

Reading the result

The result states the footprint in the receiver plane and shows the near edge, beam centre and far edge separately. A ray can be finite, approximate, parallel, point above the horizontal, behind the antenna or rejected by the 4/3-earth check. A rejected ray keeps its flat-earth figure only as a reference; it is not a usable curved-earth landing.

Limits

  • The half-power edges are pattern points, not the edge of coverage. Reception depends on the link budget, terrain, obstructions and the receiver.
  • The calculator uses flat-earth geometry and uses a 4/3-earth model only to identify where that reading stops applying and roughly how much it understates the crossing.
  • Mechanical tilt is interpreted in the boresight cut. The calculator does not model terrain, reflections, antenna gain or a measured received-signal threshold.

Next

For a link-budget range estimate, open the Coverage Calculator. If you need an antenna choice or a measured-pattern interpretation, send the inputs and datasheet reference through Request engineering review (free).