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Angular Resolution

Figure 1: The distance SA depends on the slant-range

Figure 1: The distance SA depends on the slant-range

Figure 1: The distance SA depends on the slant-range

What is the radar angular resolution?

Angular Resolution

Angular resolution is the minimum angular separation at which two equal targets can be separated when at the same range. The angular resolution characteristics of a radar are determined by the antenna beam width represented by the -3 dB angle Θ which is defined by the half-power (-3 dB) points. The half-power points of the antenna radiation pattern (i.e. the -3 dB beam width) are normally specified as the limits of the antenna beam width for the purpose of defining angular resolution; two identical targets at the same distance are, therefore, resolved in angle if they are separated by more than the antenna -3 dB beam width.

An important remark has to be made immediately: the smaller the beam width Θ, the higher the directivity of the radar antenna. The angular resolution as a distance between two targets calculate the following formula:

SA ≥ 2R · sin Θ with Θ = antenna beam width (Theta)
SA = angular resolution
       as a distance between two targets
R = slant range aim - antenna [m]


The angular resolution of targets on an analogue PPI display, in practical terms, is dependent on the operator being able to distinguish the two targets involved. Systems having Target-Recognition feature can improve their angular resolution. Cause such systems are able to compare indivual Target-Pulse-Amplitudes.

Example given:

The beam width of a radar antenna may be easily estimated even to persons that don't have an affinity for radar technology. For a rough calculation, you can use the ratio of the wavelength to the antenna size.

The air traffic radar ASR-910, operates in a frequency range of 2700 to 2900 MHz, which corresponds to a wavelength of about 11 cm. (In most cases this also corresponds to approximately 4/3 of the width of the waveguides to the antenna radiators.)
The parabolic reflector is about 4 m wide, roughly estimated.

sin Θ ≈ λ mit λ = 4/3 of the approximate width of the waveguide feeder
d = approximate width of the parabolic reflector


The ratio of both quantities is then about 0.03. According to equation (2) gives sin-1(0,03) a beam width of 1.72 degrees. That's a very good approximation compared to the manufacturer information of 1.55 degrees. This estimated value as the basis for calculating the azimuth resolution gives a necessary target distance of 900 m at a distance of 30 km (with an error of estimation of about 10 percent here).