Primary Radar Engineering Program
PREP2
(Radar/EW Simulation)
RADAR Simulation Software
Introduction
PREP uses CBT to enable students and engineers to vary radar parameters, and to observe the effects on
an active radar screen. PREP uses standard displays and signal processing techniques, which help to familiarize
the user with typical modern pulsed radar systems.
PREP consists of several simulated Line Replaceable Units (LRUs), as follows:
· Antenna
· Transmitter
· Receiver
· Synchronizer/Exciter
· Control & Display Unit
A near real-time Simulator is included, with a user definable target environment, and a Blake Chart,
all of which can be accessed via the Main Form.
The Main Form
Once the program is running, you will be presented with the Main Form shown below:
The Main Form has graphic images representing the Line Replaceable Units (LRUs), plus a menu bar with several drop-down dialogues.
Place the cursor over an LRU and a tool tip will appear with the name of the LRU.
To access the parameters for a particular LRU, either click on the graphic, or select the LRU from the 'Radar Characteristics' menu list.
The three LRUs in the middle of the Main Form are:
· The Transmitter
· The Synchronizer/Exciter
· The Receiver
The Antenna is shown on the left of the Main Form; the Control & Display Unit is shown on the right of the Main Form.
Data Entry
The format of all LRU Forms is the same; the user can enter data into the white text boxes, and select/deselect various option
or features by clicking on the relevant item. Computed or referenced values are shown in grey boxes. All grey boxes are
updated by clicking on 
or the 
button, as appropriate.
The Antenna Characteristics Form
Antenna Width (m) and Height (m) can be varied, and will affect the Antenna Gain (dB) and 3dB Beamwidth (Az).
Antenna Switch Loss (dB) and Plumbing Loss (dB) will affect the Maximum Effective Range of the radar.
Scan Width (Degrees) determines the azimuth extent of both the simulator scan, and the Range Markers.
Scan Speed (Deg/sec), in conjunction with Beamwidth, and PRF, determines the number of Hits per Scan of the radar.
The Antenna Type option buttons allow you to select one of three types of antenna - Parabola, Cassegrain
or Phased Array. Each one has its own Antenna Efficiency (%), and 1st Sidelobe level.
The (azimuth) Scan Type is dependant on the Antenna Type, with Cassegrain and Parabolic antennas only
being capable of Mechanical scanning, whereas a Phased Array scan can be Electronic or Mechanical.
Once the antenna type has been selected, and the parameters entered into the white text boxes, press the 
button to update the grey (computed) fields.
The resulting antenna radiation patterns can be viewed in Azimuth, Elevation, or 3D by clicking on the
‘View’ menu on the Main Form, and selecting the appropriate item from the drop-down list.
Examples of the Azimuth Gain Plot and the 3D Log Gain plots are shown here,
The Transmitter Form
The Transmitter is basically an RF power amplifier, which boosts the power level of the signal
generated in the Synchronizer/Exciter. Peak Power, in conjunction with the Pulse Width (PW)
and Pulse Recurrence Frequency (PRF) affects the Mean Power level. The value entered for
Peak Power is automatically transferred to the Blake Chart, to assist with computation of the
Effective Maximum Range of the radar.
The Synchronizer/Exciter Form
With Pulse Compression Coding selected to 'None' the PRF and PW values entered
here are used to calculate the Duty Cycle, and (in conjunction with Peak Power)
Mean Power. The PW determines the Range Resolution and the RF Bandwidth
requirement of the radar. The Carrier Frequency determines the RF Wavelength.
PW and RF Wavelength are automatically transferred to the Blake Chart to aid computation of the Maximum Effective Range of the radar. Once a suitable set of values have been determined, they can be entered into one of the Range Settings in the CDU Form for use in the Simulator.
Pulse Compression Coding
When Pulse Compression Coding is set to either 'Barker' or 'Linear FM', the Range Resolution (m)
and optimum Receiver RF Bandwidth (MHz) are modified by the value of the selected coding scheme.
The effective Compressed Pulse Width (μs) and the Processing Gain (dB) are also calculated.
For Barker (phase) coding, there are four selectable values (5, 7, 11 and 13) for the number of 'bits' in the pulse.
For Linear FM, the Deviation can be set anywhere between 0.1MHz and 10MHz. However, if the Deviation
is set at a value less than the reciprocal of the uncompressed pulse width, no processing gain or resolution enhancement will be obtained.
The Receiver Form
The Receiver Noise Factor (dB), IF Bandwidth (MHz) and Rx Temperature all combine to determine the Rx Noise Level (dBm).
The Rx Gain (dB) and Rx Threshold (V), in conjunction with the Rx Noise Level (dBm), determine the Threshold/Noise Ratio (dB) for the radar. This is, for practical purposes, the same as the minimum signal/noise ratio for the radar.
The Probability of False Alarm (Pfa) shown here is based on the T/N Ratio.
Various Signal Processing options such as IAGC, CFAR, FTC, and STC can be enabled in the Simulator by checking the appropriate box.
The Gain Type for the radar can be set to Linear or Logarithmic. In either case, the Receiver amplifiers saturate at a signal level of 10V.
The Control and Display Unit Form
This Form allows the user to enter four sets of values of PRF (kHz), PW (μs) and
Maximum Range (km) for use in the Simulator.
Pulse Compression can also be selected on Ranges 3 and 4.
The Simulator Display Type can be selected to either Sector Scan or B Type.
An A-Scope display is permanently available on the Simulator.
Range Markers and a Freeze Button can be enabled on the Simulator by checking
the appropriate boxes on this Form.
Once all of the characteristics have been entered, select 
to transfer them
to the PREP Simulator database.
The Radar Simulator Form
The Simulator has four Range buttons, which correspond with the four Range Settings
in the Control & Display Unit Form. The selected Maximum Range (RMax km)
is shown on the Simulator screen, along with the current value of Gain and T/Hold (Threshold).
The Gain 
and Threshold 
can be varied by clicking on the + or - sign of the appropriate
control, or by opening the Receiver Form and using the slider controls.
The buttons corresponding to the Signal Processing options enabled in the Receiver Form
are displayed in the Processing frame.
FTC, IAGC and CFAR are mutually exclusive; however STC can be used in combination
with any of the other processing options, or on its own.
If the Freeze and Range Markers options are checked in the Receiver Form, then the
Freeze and MKRS buttons will be visible on the Simulator Form. Clicking on the MKRS
button will toggle the Range Markers (light green) on and off.
To run the Simulator, click on the 
button, which will become yellow, and display
The radar antenna scan will begin, and the antenna Azimuth (bearing) will be updated and
displayed (Az) on the Simulator screen.
The A-Scope 
shows the signal amplitude vs range, as well as showing the
current Rx Threshold setting (in red).
The Sector Scan or B Type displays, show any signals above the Rx Threshold, as range vs bearing.
B Type Display
The display can be frozen at any time during the scan by clicking on the Freeze button, the Freeze function can be reset by clicking the button again.
To stop the Simulator before the end of a scan, click on the 
button, which will revert to 
.
To clear the screen at any time, click on the button.
The Blake Chart Form
The Blake Chart shown below is accessed via the 'Radar Characteristics' drop down menu.
The Blake Chart is used by radar designers to predict the Maximum Radar Range, that is,
the maximum range at which the specified target can be detected. This electronic version closely
follows the original format devised by Blake.
Maximum Radar Range Plot
Target Data
The 'Target Data' menu option opens the Form shown below, which contains the parameters
for Targets 1 & 2, Noise Sources 1 & 2, a Target 1 Repeater, and a Chaff Cloud. The parameters
for all of these can be varied by typing in the new value, and clicking on 
The Noise Sources, Target 1 Repeater, and the Chaff Cloud are turned on by clicking on the appropriate checkbox.
The Noise Sources can also be mounted on the targets by checking the ‘Mount on Tgt’ checkbox. This will
grey out the Bearing and Range text boxes, and set their values to the same as those of the relevant target.
The Repeater source is always mounted on Tgt 1 and can be set to 1, 2 or 3 Repeats. The Gain of
the Repeater is variable between -60 to +60dB, and the Delay between each repeat is variable between 0.1us and 30us.
The Chaff Cloud can be positioned anywhere in the 120 degree field of view. The Weight of Chaff in grams is entered,
along with the dimensions of the desired cloud.
Once all of the desired Target/Noise/Repeater/Chaff values have been entered, selecting 
will calculate
the Volume of the Chaff Cloud, the RCS per cubic metre, and transfer these values to the PREP Simulator database
A selection of simulation exercises are supplied with PREP.
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