المبادى الأساسية للرادار ::: Basic Radar Principles
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رد: المبادى الأساسية للرادار ::: Basic Radar Principles
الي يفول الاخ ليس تشويش وانما نقص مستوى الرد او ما يسمى بالحالات الخاطئة fausse alarme وهي يا تعود لسوء الاحوال الجوية و عدم معرفة تضاريس المنطقة كل هذه العوامل كانت في الرادار في الحرب العالمية الثانية لاكنها تحسنت باضافة برمجيات وادخال لوغاريتمات التعقب وادخال علوم الاحتمالات من اجل الغاء الحالات الخاطئة
والراداد اللي طارحه الاخ هو الرادار الاساسي يمكن كل واحد منا بيعمله باستعمال microwave micronde او السخان اللي في البيت بالاضافة الى تلفزيون و دش الفضائية انا شخصيا عملت في الاعمال التطبيقية في الجامعة تحت اشراف الاستاذ طبعا في دائرة الطيران
اصبروا علي لابحث لكم عن دروس لي في الموضوع
الي يفول الاخ ليس تشويش وانما نقص مستوى الرد او ما يسمى بالحالات الخاطئة fausse alarme وهي يا تعود لسوء الاحوال الجوية و عدم معرفة تضاريس المنطقة كل هذه العوامل كانت في الرادار في الحرب العالمية الثانية لاكنها تحسنت باضافة برمجيات وادخال لوغاريتمات التعقب وادخال علوم الاحتمالات من اجل الغاء الحالات الخاطئة
والراداد اللي طارحه الاخ هو الرادار الاساسي يمكن كل واحد منا بيعمله باستعمال microwave micronde او السخان اللي في البيت بالاضافة الى تلفزيون و دش الفضائية انا شخصيا عملت في الاعمال التطبيقية في الجامعة تحت اشراف الاستاذ طبعا في دائرة الطيران
اصبروا علي لابحث لكم عن دروس لي في الموضوع
- إنضم
- 21 ديسمبر 2009
- المشاركات
- 368
- التفاعل
رد: المبادى الأساسية للرادار ::: Basic Radar Principles
10.4.1. Multiple MTI Chaff Mitigation Technique1
In this section, an algorithmic (schema) approach for detecting and tracking
targets in highly cluttered environments is presented. The approach is to accurately
track the centroid of the chaff cloud using a combination of medium
band (MB) and wide-band (WB) range resolution radar waveforms.
At moderate Pulse Repetition Frequencies (PRFs), differential target velocities
(about the centroid of the chaff cloud) are detected and tracked via Doppler
banks of transversal filters that are tuned to detect the target velocity differ-ences. Through sensitivity analysis models, the theoretical lower bound on
detectable differential target velocity as a function of the chaff cloud composition
(e.g., clutter cross section, clutter spectral width, number of dipoles, and
clutter velocity standard deviation) and radar related parameters (e.g., waveform
frequency, bandwidth, integration times, PRFs, and signal-to-clutter
ratio) are analyzed.
Overview
A five-step approach for detecting and tracking targets in highly cluttered
environments has been developed. The five steps are:
1. Utilize a 1 to 5 percent MB bandwidth, high PRF radar waveform, to measure
the chaff cloud range extent, centroid, and velocity growth rate.
2. Establish track on the centroid of the chaff cloud with the MB waveform.
3. Based on course track information obtained in steps 1) and 2), implement
WB track (10% or greater bandwidth waveform) on the cloud centroid.
4. Design a doppler bank of Moving Target Indicator (MTI) transversal filters
to provide adequate gain at specific velocity increments about the WB centroid
track.
5. Process the Multiple MTI (M2) doppler filters in parallel to detect differences
in target Doppler (with respect to the cloud centroid track velocity).
Targets are detected when integration at the correct Doppler difference
occurs.
Operational concerns that have been identified for implementation of this
approach include: (1) the ability of a radar to adequately track the centroid of
the chaff cloud (i.e., track precision); (2) the ability of a radar to detect small
differences in target Doppler relative to the chaff cloud centroid (i.e., Doppler
precision); and (3) the ability of a filter (in this case, a bank of MTI’s) to
achieve the necessary processing gain to detect the target
Theoretical tracking accuracy of a chaff cloud
The single pulse thermal-noise error in a velocity tracking measurement
for optimum processing can be described by
(10.28)
where is the pulsewidth and is that for the target in track. To detect targets
in clutter, substitute the difference-channel chaff-to-signal ratio for .
More precisely,
(10.29)
σf
σf
1
1.81τ 2 × SNR
= --------------------------------------
τ SNR
SNR
σf
1
1.81τ 2 × Cchaff ⁄ SMultiple MTI (M2) Doppler Filter Design
The M2 Doppler filter design is derived from the theoretical N-tap delay line
MTI canceller. The general formula for the improvement factor was derived in
Chapter 7 (Section 7.7.2). A bank of MTI Doppler filters that cover the frequency
range from 0 to the PRF will achieve performance beyond that of a
conventional MTI. The weights are given by:
(10.30)
where the index is between 0 to N-1 and corresponds to the MTI Doppler
filter bank. In this design, a 5-tap delay line MTI filter is considered. The transfer
function for the overall Doppler bank is
(10.31)
σf Cchaff ⁄ S τ
Figure 10.8. Single pulse thermal noise error versus Cchaff ⁄ S and τ .
N
Wi, k e
j2π(i 1)
k ⁄ N
------------------------
=
k N
Hk(f) e(j2π)(i 1)(fT k ⁄ N)
i = 1
N
= Σ
10.4.1. Multiple MTI Chaff Mitigation Technique1
In this section, an algorithmic (schema) approach for detecting and tracking
targets in highly cluttered environments is presented. The approach is to accurately
track the centroid of the chaff cloud using a combination of medium
band (MB) and wide-band (WB) range resolution radar waveforms.
At moderate Pulse Repetition Frequencies (PRFs), differential target velocities
(about the centroid of the chaff cloud) are detected and tracked via Doppler
banks of transversal filters that are tuned to detect the target velocity differ-ences. Through sensitivity analysis models, the theoretical lower bound on
detectable differential target velocity as a function of the chaff cloud composition
(e.g., clutter cross section, clutter spectral width, number of dipoles, and
clutter velocity standard deviation) and radar related parameters (e.g., waveform
frequency, bandwidth, integration times, PRFs, and signal-to-clutter
ratio) are analyzed.
Overview
A five-step approach for detecting and tracking targets in highly cluttered
environments has been developed. The five steps are:
1. Utilize a 1 to 5 percent MB bandwidth, high PRF radar waveform, to measure
the chaff cloud range extent, centroid, and velocity growth rate.
2. Establish track on the centroid of the chaff cloud with the MB waveform.
3. Based on course track information obtained in steps 1) and 2), implement
WB track (10% or greater bandwidth waveform) on the cloud centroid.
4. Design a doppler bank of Moving Target Indicator (MTI) transversal filters
to provide adequate gain at specific velocity increments about the WB centroid
track.
5. Process the Multiple MTI (M2) doppler filters in parallel to detect differences
in target Doppler (with respect to the cloud centroid track velocity).
Targets are detected when integration at the correct Doppler difference
occurs.
Operational concerns that have been identified for implementation of this
approach include: (1) the ability of a radar to adequately track the centroid of
the chaff cloud (i.e., track precision); (2) the ability of a radar to detect small
differences in target Doppler relative to the chaff cloud centroid (i.e., Doppler
precision); and (3) the ability of a filter (in this case, a bank of MTI’s) to
achieve the necessary processing gain to detect the target
Theoretical tracking accuracy of a chaff cloud
The single pulse thermal-noise error in a velocity tracking measurement
for optimum processing can be described by
(10.28)
where is the pulsewidth and is that for the target in track. To detect targets
in clutter, substitute the difference-channel chaff-to-signal ratio for .
More precisely,
(10.29)
σf
σf
1
1.81τ 2 × SNR
= --------------------------------------
τ SNR
SNR
σf
1
1.81τ 2 × Cchaff ⁄ SMultiple MTI (M2) Doppler Filter Design
The M2 Doppler filter design is derived from the theoretical N-tap delay line
MTI canceller. The general formula for the improvement factor was derived in
Chapter 7 (Section 7.7.2). A bank of MTI Doppler filters that cover the frequency
range from 0 to the PRF will achieve performance beyond that of a
conventional MTI. The weights are given by:
(10.30)
where the index is between 0 to N-1 and corresponds to the MTI Doppler
filter bank. In this design, a 5-tap delay line MTI filter is considered. The transfer
function for the overall Doppler bank is
(10.31)
σf Cchaff ⁄ S τ
Figure 10.8. Single pulse thermal noise error versus Cchaff ⁄ S and τ .
N
Wi, k e
j2π(i 1)
k ⁄ N
------------------------
=
k N
Hk(f) e(j2π)(i 1)(fT k ⁄ N)
i = 1
N
= Σ
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