A stepped frequency pulse waveform consists of a series of N narrowband pulses. The frequency is increased from step to step by a fixed amount, Δf, in Hz.
Similar to linear FM pulse waveforms, stepped frequency waveforms are a popular pulse compression technique. Using this approach enables you to increase the range resolution of the radar without sacrificing target detection capability.
To create a stepped FM pulse waveform, use
The stepped frequency pulse waveform has the following modifiable properties:
SampleRate — Sampling
rate in Hz
PulseWidth — Pulse duration
PRF — Pulse repetition
frequency in Hz
FrequencyStep — Frequency
step in Hz
NumSteps — Number of frequency
OutputFormat — Output
format in pulses or samples
NumSamples — Number of
samples in the output when the
NumPulses — Number of
pulses in the output when the
This example shows how to create and plot a 5-step Stepped FM pulse waveform. Set the pulse width (duration) to 50 μs, the pulse repetition frequency (PRF) to 10 kHz, and the frequency step to 20 kHz. The sampling rate is 1 MHz. By default the
OutputFormat property is set to
'Pulses' and the number of pulses in the output is set to one.
Note: This example runs only in R2016b or later. If you are using an earlier release, replace each call to the function with the equivalent
step syntax. For example, replace
waveform = phased.SteppedFMWaveform('SampleRate',1e6,... 'PulseWidth',50e-6,'PRF',10e3,... 'FrequencyStep',20e3,'NumSteps',5);
bandwidth function to show that the bandwidth of the stepped FM pulse waveform is the product of the frequency step and the number of steps.
ans = 100000
OutputFormat property is set to 'Pulses' and the
NumPulses property is set to one, executing the System object™ returns one pulse repetition interval (PRI). The pulse duration within that interval is set by the
PulseWidth property. The remainder of the PRI consists of zeros.
The frequency of the initial pulse is zero Hz (DC). With the
NumPulses property set to one, each time you execute the System object™, the frequency of the narrowband pulse increments by the value of the
FrequencyStep property. If you execute the System object more times than the value of the
NumSteps property, the process repeats, starting over with the DC pulse.
Execute the System object to return successively higher frequency pulses. Plot the pulses one by one in the same figure window. Pause the loop to visualize the increment in frequency with each execution of the System object. Execute the System obkect one more time than the number of pulses to demonstrate that the process starts over with the DC pulse.
This figure shows the pulse plot for the last iteration of the loop.
t = unigrid(0,1/waveform.SampleRate,1/waveform.PRF,'[)'); for i = 1:waveform.NumSteps plot(t,real(waveform())) pause(0.5) axis tight end
This plot shows how the pulse returns to its DC value.