Inverse Synthetic Aperture Radar Imaging With MATLAB Algorithms. Caner Ozdemir

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Inverse Synthetic Aperture Radar Imaging With MATLAB Algorithms - Caner Ozdemir


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signal and receiving the backscattered wave from the target (see Figure 2.7). Therefore, the antenna gains, G1 and G2 in Eq. 2.30, become identical, say G(= G1 = G2). Similarly, the target distance from the transmitter and the receiver distance from the target becomes equal, say R (= R1 = R2). Then the radar range equation can be obtained in its simplified form as shown below:

Schematic illustration for obtaining monostatic radar range equation.

Graph depicts receiver power corresponding to maximum range of radar.

      (2.33)equation

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

      (2.34)equation

      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)equation

      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.

      2.5.1 Signal‐to‐Noise Ratio

      Similar to all electronic devices and systems, radars must function in the presence of internal noise and external noise. The main source of internal noise is the agitation of electrons caused by heat. The heat inside the electronic equipment can also be caused by environmental sources such as the sun, the earth, and buildings. This type of noise is also known as thermal noise (Johnson 1928) in the electrical engineering community.

      (2.36)equation

      Here, k = 1.381 × 10−23 W/K° is the well‐known Boltzman constant, and Teff is the effective noise temperature of the radar in degrees Kelvin (K°). Teff is not the actual temperature but is related to the reference temperature via the noise figure, Fn, of the radar as

      (2.37)equation

      where the reference temperature, To, is usually referred to as room temperature (To ≈ 290 K°). Therefore, noise power spectral density of the radar is then being equated to

      (2.38)equation

      To find the value of the noise power, Pn, of the radar, it is necessary to multiply No with the effective noise bandwidth, Bn, of the radar as shown below:

      (2.40)equation

      The above equation is derived for the bistatic radar operation. The equation can be simplified to the following for the monostatic radar setup:

      (2.41)equation

      The selection of the radar signal type is mainly decided by the specific role and the application of the radar. Therefore, different waveforms can be utilized for the various radar applications. The most commonly used radar waveforms are

      1 continuous wave (CW),

      2 frequency‐modulated


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