radar:doppler
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| radar:doppler [2018/06/05 19:48] – masrour | radar:doppler [2026/04/28 15:13] (current) – external edit 127.0.0.1 | ||
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| + | ===== Moving Target Detector ===== | ||
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| - | * **MTI Improvement Factor** ($I_C$) : | + | * **MTI Improvement Factor** ($I_C$) : |
| The signal-to-clutter ratio at the output of the MTI system divided by the signal-to-clutter ratio at the input averaged uniformly over all target radial velocities of interest. (discussed earlier) | The signal-to-clutter ratio at the output of the MTI system divided by the signal-to-clutter ratio at the input averaged uniformly over all target radial velocities of interest. (discussed earlier) | ||
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| $SCV = (C/S)_{in}$ | $SCV = (C/S)_{in}$ | ||
| - | * **Clutter Visibility Factor ($V_{OC}$)** : | + | * **Clutter Visibility Factor ($V_{OC}$)** : |
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| The Signal to Clutter ratio after filtering that provides the specified $P_d$ and $P_{fa}$. | The Signal to Clutter ratio after filtering that provides the specified $P_d$ and $P_{fa}$. | ||
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| When the MTI improvement factor is not great enough to reduce the clutter sufficiently..the clutter residue will appear on the display and prevent the detection of aircraft targets whose cross sections are larger than the clutter residue. | When the MTI improvement factor is not great enough to reduce the clutter sufficiently..the clutter residue will appear on the display and prevent the detection of aircraft targets whose cross sections are larger than the clutter residue. | ||
| - | Whereby setting the limit level $ L$, relative to the noise $ N$, equal to the MTI improvement factor $I$ or $L/N = 1$. If the limit level relative to noise is set higher than the improvement factor. clutter residue obscures part of the display and If it is set too low there may be a " black hole " effect on the display. The limiter provides a **c**onstant **f**alse **a**larm **r**ate (**CFAR**) and is essential to usable MTI performance. | + | Whereby setting the limit level $L$, relative to the noise $N$, equal to the MTI improvement factor $I$ or $L/N = 1$. If the limit level relative to noise is set higher than the improvement factor. clutter residue obscures part of the display and If it is set too low there may be a " black hole " effect on the display. The limiter provides a **C**onstant **F**alse **A**larm **R**ate (**CFAR**)[(A **false alarm** is “an erroneous radar target detection decision caused by noise or other interfering signals exceeding the detection threshold”. In general, it is an indication of the presence of a radar target when there is no valid aim. The False Alarm Rate (FAR) is calculated using the following formula: $FAR=\frac{false targets per PRT}{Number of rangecells}$)] |
| Unfortunately, | Unfortunately, | ||
| - | An example of the effect of limiting is shown in the $Fig.48$, which plots the improvement factor for two-pulse and three-pulse cancelers within various levels of limiting. The abscissa applies to a Gaussian clutter spectrum that is generated either by clutter motion with standard deviation $ σ_v$, at a wavelength $λ$ and a prf $f_p $, or by antenna scanning modulation with a Gaussian-shaped beam and $n_B$ pulses between the half-power beamwidth of the one-way antenna pattern. The parameter $C/L$ is the ratio of the RMS clutter power to the receiver-IF limit level. | + | An example of the effect of limiting is shown in the $Fig.47$, which plots the improvement factor for two-pulse and three-pulse cancelers within various levels of limiting. The abscissa applies to a Gaussian clutter spectrum that is generated either by clutter motion with standard deviation $ σ_v$, at a wavelength $λ$ and a prf $f_p $, or by antenna scanning modulation with a Gaussian-shaped beam and $n_B$ pulses between the half-power beamwidth of the one-way antenna pattern. The parameter $C/L$ is the ratio of the RMS clutter power to the receiver-IF limit level. |
| The loss of improvement factor increases with increasing complexity of the canceler. | The loss of improvement factor increases with increasing complexity of the canceler. | ||
| - | Thus the added complexity of higher-order cancelers is seldom | + | Thus the added complexity of higher-order cancelers is not often justified in such situations. The linear analysis of MTI signal processors is therefore not enough |
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| - | The **M**oving **T**arget **D**etector, | + | The **M**oving **T**arget **D**etector, |
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| - | \begin{equation} | + | |
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| - | \end{equation} | + | |
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| - | Where, $W = M^{-1}s^{\ast }$ and $M = I$ , | + | |
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| - | \begin{equation} | + | |
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| - | \end{equation} | + | |
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| - | therefore Duppler Frequency-response Function will be | + | |
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| - | \begin{equation} | + | |
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| - | \end{equation} | + | |
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| + | The output of the receiver is a signal, which contains the required target plus various forms of noise and clutter. In the case of the MTI output, this clutter residue is the result of imperfect cancellation due to various factors such as equipment instability, | ||
| + | The diagram shows the location of the detector in the chain of signal processing. This device forms the information on a point like target as a digital report. The up to this point existing information about the analog value (or digital description of) of the received power in a particular binary cell will be transformed to information about the coordinates of a target. The value of the power is included in this report mostly. | ||
| + | The important procedure is, that up to this point all binary cells (containing the received power) must be processed. After the detector exist only reports about selected binary cells. However, there may exist several reports about a single target, generated by adjacent binary cells. This will processed in the next device. | ||
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| + | Until now its simply discused about MTI performance limitiation ,MTD device operation and using different filters or transformation.deeper discussion on the Doppler frequency and adaptive thresholds on the different filters ,etc. __is presented in__ | ||
| - | More information is presented in **Modern Radar System Analysis** | + | * |
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