Analyze performance characteristics of pulsed, frequency modulated, and phase-coded waveforms
The Radar Waveform Analyzer app lets you explore the properties of signals that are commonly used in radar and sonar systems, and to produce plots and images to visualize waveforms.
The app lets you determine the basic characteristics of these waveforms
Linear frequency modulation (LFM)
Frequency modulation constant waveform (FMCW)
You can quickly modify parameters for each waveform, such as pulse repetition frequency (PRF), sample rate, pulse duration, and bandwidth. You can also set the propagation speed to represent electromagnetic waves, or sound waves in air or water.
After you configure parameters, the app displays basic waveform characteristics such as range resolution, Doppler resolution, and maximum range. It also can generate a variety of plots and images to visualize the waveform, including:
Real and imaginary components
Magnitude and phase
Ambiguity function (AF) representations, including contour, surface, delay cut, and Doppler cut
MATLAB® Toolstrip: On the Apps tab, under Signal Processing and Communications, click the app icon.
MATLAB command prompt: Enter
This example shows how to analyze a rectangular waveform.
In the Waveform Settings panel, set the Waveform to
An ideal rectangular waveform jumps instantaneously to a finite value and stays there for some duration.
Assume the radar is designed for a maximum range of 50 km.
For this range, the time for a signal to propagate to that range and return is 333 μs. Therefore, you must allow 333 μs between pulses, equivalent to a maximum pulse repetition frequency (PRF)) of 3000 Hz.
Set the Pulse Width to 50 μs.
With these values, the app displays a 7.5 km range resolution.
The resolution of a rectangular pulse is roughly 1/2 the pulse-width multiplied by the speed of light, which is entered here in the Propagation Speed field as 300e6 m/s. The Doppler resolution is approximately the width of the Fourier transform of the pulse.
The same analysis can be used for sonar if you assume a much smaller speed of propagation, 1500 m/s.
The following figure shows the real and imaginary parts of the waveform. This is the default view on the View drop-down list.
Next, you can view the signal spectrum. To do so, select
the View drop-down menu.
Finally, you can display the joint range-Doppler resolution
Ambigity-Function Surface from the View pull-down
menu in the Visualization Settings panel.
This example shows how to improve range resolution using a linear FM waveform.
In the previous example, the range resolution of the rectangular pulse was poor, at 7.5 km. You can improve the range resolution by choosing a signal with a larger bandwidth. A good choice is a linear FM pulse.
Set the Waveform to
This pulse has a variable frequency which can either increase or decrease as a linear function of time.
Choose the Sweep Direction as
and the Sweep Bandwidth as 1 MHz.
You can see that keeping the same pulse width as before improves the range resolution to 150 m, as shown in the following figure.
Examine the ambiguity function which shows a trade-off.
While the range resolution is better, the Doppler resolution is worse than that of a rectangular waveform.
This example shows how to display the spectrogram of a linear FM waveform with and without frequency reassignment.
Use the same signal parameters as in the previous example.
Spectrogram from the View drop-down
menu in the Visualization Settings panel. Then, click the Reassigned checkbox
to show the frequency reassigned spectrogram (reassignment is turned
on by default). Frequency reassignment is a technique for sharpening
the magnitude spectrogram of a signal using information from its phase
spectrum. For more information on frequency reassignment, see Fulop
and Kelly (2006).
You can vary the Threshold Value setting to show or hide weaker spectrum components.
To view the conventional spectrogram, click the Reassigned checkbox again.
Again, you can vary the Threshold Value setting to show or hide weaker spectrum components.
 Fulop, Sean A., and Kelly Fitz. "Algorithms for computing the time-corrected instantaneous frequency (reassigned) spectrogram, with applications." Journal of the Acoustical Society of America. Vol. 119, January 2006, pp. 360–371.