#### Angular Resolution

Figure 1: The distance S_{A} depends on the slant-range

Figure 1: The distance S_{A} 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:

S_{A} ≥ 2R · sin |
Θ | with | Θ = antenna beam width (Theta) S _{A} = angular resolutionas a distance between two targets R = slant range aim - antenna [m] |
(1) |

2 |

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 |
(2) |

d |

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).