Читать книгу Inverse Synthetic Aperture Radar Imaging With MATLAB Algorithms - Caner Ozdemir - Страница 63

While working with radars, another important parameter that should be carefully considered is the detection range of radar, that is, the farthest distance of the target that can be detected over the noise floor of the radar. This distance can be easily calculated starting from the radar range equation. Let us rewrite Eq. 2.31 in terms of antenna effective aperture, A_eff = 4π ⋅ G₂/λ², as

(2.32)

The minimum power at the receiver output can only be detected if the received signal is greater than the noise floor, as demonstrated in Figure 2.8. If the power level at the receiver output is lower than the noise floor, this signal cannot be distinguished from the noise mostly produced by the environment and the electronic equipment and therefore can either be considered as noise or clutter.

Figure 2.8 Minimum receiver power corresponding to maximum range of radar.

Considering that the input power to the radar remains unchanged, the output power at the receiver in Eq. 2.32 is selected as the minimum detectable signal, P_min, for the maximum range distance of R_max as

(2.33)

Therefore, it is easy to find the maximum range of radar by rearranging the above equation to leave R_max alone as

(2.34)

The above equation gives the maximum range of an object that can be detectable by the radar. The meaning of “maximum range” is clarified with the following example: For a radar antenna with 26 dB gain at 10 GHz, the corresponding antenna effective area becomes 28 472 m². If the input power of this monostatic radar is 75 W with a receiver sensitivity of −55 dBmW (3.16 nW) and used to detect a target with an RCS of 0.5 m² at 10 GHz, then the maximum range can be readily calculated by plugging the appropriate numbers into above equation to give

(2.35)

If this target is located at the range closer than 170.78 km (~171 km), then it will be detected by this radar. However, any object that has a maximum RCS of 0.5 m² and located beyond 171 km will not be perceived as a target since the received signal level will be lower than the sensitivity level (or the noise floor) of the radar as illustrated in Figure 2.8.