This example shows how to set up a radar system simulation consisting of the transmitter, channel with target and a receiver. This is a key multi- discipline problem in the Aerospace Defense industry. The RF sections in the transmitter and receiver are modeled using SimRF.
This example requires the following products:
Signal Processing Toolbox
DSP System Toolbox
Communications System Toolbox
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The system consists of:
A radar pulse generator, which outputs a chirp with a power of 1 mW at 2% duty cycle(On time = 2 ms, period = 100ms).
An RF transmitter section consisting of a filter and amplifier. This section is implemented by using blocks from the SimRF circuit envelope library. Since the filter is a linear device and the amplifier being non-linear we split them up and house them in two independent subsystems. In addition the set of simulation frequencies is different in both subsystems as we require more frequencies in the non-linear subsystem to capture the effect of a finite IP3. It is important to note that this approach represents a trade-off between an increase in simulation speed and the loss of inter-stage loading effects available in a cascaded chain.
An ideal antenna element with specified boresight gain, operating at 2.1 GHz.
The Target is a theoretical implementation of a moving target that fully reflects the entire incident signal off of its cross- sectional surface. The surface is perpendicular to the direction of travel of the incident radar pulses.
The RF Receiver is built using the SimRF Circuit Envelope library. A direct conversion structure is implemented in the receiver together with an LNA and matching networks. A touchstone file is used to model the LNA (receiveamp.s2p). The local oscillator includes a phase noise model. Similar to the RF transmitter we have split the model into independent linear and non-linear subsystems such that, the matching networks, LNA and filter are in the linear section, while the mixers and final stage amplifiers are in the non-linear section.
The Receive Module in this example serves two purposes. First, the module contains a matched filter detector for target detection. Also, this module serves as a testbench where a theoretical filter implementation is realized via Simulink blocks, the output of each of these filters is compared, and the difference is plotted.
Set the target cross section, target speed, and relative distance to the target by double-clicking the Target icon and specifying the corresponding parameters. At sufficiently large distances, the return signal can not be detected within the noise. Similarly, the return signal can not be detected in the noise if the target cross section is too small.
To start the example:
Select Simulation > Run
The scope output shows the results from a 0.5s simulation, with the received pulses indicating the presence of the target.
Open the 'Ideal Antenna' block and change the transmit gain to 10 dB in the dialog.
This indicates that the target will no longer receive the signal from the main beam of the transmit antenna.
To run the example under this scenario:
Select Simulation > Run
The effect of the change in antenna gain is observed in the scope. Notice that the pulses are now buried in the noise thus rendering the object electromagnetically invisible.
Open the Receiver Front-End subsystem, and use the manual switch to include the phase noise model for the Local Oscillator.
The effect of the phase noise from the Local oscillator is observed in the varying strength of the detected pulses. This varying pulse strength can have an impact on the probability of detection and could result in the target being detected only at certain times.