This tool will calculate the maximum coverage that the antenna will cover from a specified distance and antenna's half-power beamwidth.

Calculations:

Applications:

During RF immunity testing, the product is subjected to a specific RF field strength (say 10 volts per meter) for a fixed dwell time and over a series of predetermined spot frequencies. If the half-power beamwidth of the antenna is not large enough to cover the equipment under test, then one of the following should be performed:

• Conduct multiple tests at locations along the EUT.
• Use a greater separation distance (if allowed).
• Perform the test with an antenna that has a larger half-power beamwidth.

Definitions:

Half-Power Beamwidth is the angular distance on ether side of the peak field, or main lobe, of the antenna that represents half of the peak field intinsity. Half the power is equivalent to -3dB, so the half-power beamwidth is also sometimes referred to as the 3dB beamwidth.

Separation Distance is the distance from the antenna to the product under test.

Further Reading:

• The "Selecting antenna/power amplifier combinations for the coming new RF immunity standards" article explains different power amplifier / antenna matching combinations for some new RF immunity standards.
• Here is a field intensity calculation calculation tool to help determining the actual field intensity or power density at a given distance