In radar operation, it is often necessary to adjust the operation mode based on the target return. This example shows how to model a radar that changes its pulse repetition frequency (PRF) based on the radar detection.
This example includes one Simulink® model:
PRF Agility Based on Radar Detection: slexPRFSchedulingExample.slx
This model simulates a monostatic radar that searches for targets with an unambiguous range of 5 km. If the radar detects a target within 2 km, then it will switch to a higher PRF to only look for targets with 2 km range and enhance its capability to detect high speed targets.
The system is very similar to what is used in the Simulating Test Signals for a Radar Receiver in Simulink example with the following notable difference:
The waveform block is no longer a source block. Instead, it takes an input,
idx, to select which PRF to use. The available PRF values are specified in the PRF parameter of the waveform dialog.
Each time a waveform is transmitted, its corresponding PRF also sets the time when the next pulse should be transmitted.
There is now a controller to determine which PRF to use for the next transmission. At the end of the signal processing chain, the target range is estimated. The controller will use this information to decide which PRF to choose for next transmission.
Once the model is compiled, notice that the signal passing through the system can vary in length because of a possible change of the waveform PRF.
The model takes advantage of the new controllable sample time so the system runs at the appropriate time determined by the varying PRF values.
Several dialog parameters of the model are calculated by the helper function helperslexPRFSchedulingSim. To open the function from the model, click on
Modify Simulation Parameters block. This function is executed once when the model is loaded. It exports to the workspace a structure whose fields are referenced by the dialogs. To modify any parameters, either change the values in the structure at the command prompt or edit the helper function and rerun it to update the parameter structure.
The figure below shows the detected ranges of the targets. Target ranges are computed from the round-trip time delay of the reflected signals from the targets. At the simulation start, the radar detects two targets, one is slightly over 2 km away and the other one is at approximately 3.5 km away.
After some time, the first target moves into the 2 km zone and triggers a change of PRF. Then the received signal only covers the range up to 2 km. The display is zero padded to ensure that the plot limits do not change. Notice that the target at 3.5 km gets folded to the 1.5 km range due to range ambiguity.
This example shows how to build a radar system in Simulink® that dynamically changes its PRF based on the target detection range. A staggered PRF system can be modeled similarly.