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Keysight Technologies
Designing, Verifying and Testing Stepped Frequency Radar
Systems for Commercial and A/D Applications




Application Note
Introduction

Stepped Frequency Radar (SFR) is well known for non-destructive testing and ground searching
applications. With SFR, the echoes of stepped frequency pulses are synthesized in the frequency
domain to obtain shorter pulses in the time domain. Using frequency hopping, both high resolution
and a high signal-to-clutter ratio can be achieved. As a high range resolution radar technique, SFR
offers a number of key advantages over other techniques like regular pulse radar. Such advantages
include target classification, resolution of multiple targets, accurate range profile, detection of low
radar cross section (RCS) targets in clutter, and low cost. Because of these advantages, SFR is today
widely used in both the commercial and aerospace/defense (A/D) industries.

This application note introduces a simulation platform--Keysight Technologies, Inc. SystemVue
electronic system level (ESL) design software--which easily links to measurement tools to enable the
design, validation and test of SFR systems under different environments. The simulation platform with
test environment includes return signal RCS and background clutter. A template SFR design is also
provided. SFR design is performed in SystemVue. Then, simulation results are evaluated with Tx
and Rx measurements. Users can customize the template SFR design to their own systems and run
simulations in the platform to evaluate the design's performance. The simulation platform also can
be used as a test platform for SFR component test. As an example, an SFR system with target
returns and ground clutter will be presented that uses the platform for both simulation and test. The
proposed platform works very well for design, as well as for verification and testing of SFR systems.
03 | Keysight | Designing, Verifying and Testing Stepped Frequency Radar Systems for Commercial and A/D Applications - Application Note



Problem Solution
As shown in Figure 1, SFR transmits sequences of N pulses at a Successfully designing, verifying and testing today's SFR systems
fixed pulse-repetition frequency, but not at a fixed radar frequency. under different real-world environments requires a simulation
Each pulse in the sequence of a stepped frequency waveform platform with links to a test environment that includes return
has the same pulse width and time duration, but different carrier RCS and background clutter. One such solution is the SystemVue
frequency. That frequency is given by f i = fo+N*dF, where dF is the ESL design software. As a comprehensive, model-based design
amount of frequency increased, indicating that frequency hopping environment for challenging physical layer (PHY) communications
and time division are used. systems, it integrates modeling, simulation, reference intellectual
property (IP), hardware generation, and measurement links into a
single, versatile development platform across RF and baseband
domains that transitions easily from algorithms into hardware
Freq (HZ)




verification.

fN-i SystemVue's platform-based design approach produces increased,
f
fi early confidence that SFR system designs will not only work in
the real world, but also achieve superior results, given available
fo fo
processing power, analog performance and environmental condi-
time tions. Connecting measurement equipment to SystemVue via its
T measurement links expands the concept to validation and test of
SFR systems as well.
NT
Figure 1. Shown here is a typical SFR waveform. Using SystemVue, a working reference design of the SFR system is
created and used to generate test vectors. The reference design
Using this approach, SFR systems are able to overcome the power
also processes received signals captured from live measurements.
and bandwidth limitations of simple pulsed radar. Transmitting
A signal generator and arbitrary waveform generator (AWG) then
longer pulses extends their range capability, while also retaining
render simulated signals for testing SFR hardware receivers and
the wide bandwidth needed for high resolution. In any radar
transmitters. A signal analyzer and signal analysis software (e.g.,
receiver, the received echo signals include both target returns
Keysight's 89600 Vector Signal Analysis (VSA) software), capture
and background clutter. In SFR radar, this clutter interferes with
and analyze the signals. For further analysis and signal processing,
target detection, making it difficult to find the actual number of
measured signals can be brought back into SystemVue.
targets or even fail to detect small targets. In this case, it is hard
to find a closed-form analytical solution, and as a result, simulation
becomes very important.
04 | Keysight | Designing, Verifying and Testing Stepped Frequency Radar Systems for Commercial and A/D Applications - Application Note



Example: Simulating a SFR System
As an example of how the SystemVue simulation platform can
be used to design, verify and test SFR systems, consider the SFR
system designed in Figures 2 and 3. In the signal generator, a SFR
source is followed by an RF modulator, then two target models and
a clutter model are set. The output of the signal generator simulates
the SFR received signal, including target return and clutter.




Figure 2. A stepped frequency radar simulation design is shown here.




R1 ([email protected] Models)
StepFreQType_Mode=Positive Hop
PRF=10e3Hz
Delta_Freq=4e6Hz
NumOfSteqFreq=128
SampleRate=1e9Hz
Figure 3. Illustrated here is the step frequency signal generation model.
05 | Keysight | Designing, Verifying and Testing Stepped Frequency Radar Systems for Commercial and A/D Applications - Application Note



Example: Simulating a SFR System (continued)
The received signal is measured at the input of the SFR receiver
and displayed in Figure 4. Note that the plot of frequency versus
time in Figure 4C is in keeping with what one would expect for the
SFR signals based on the carrier frequency calculation previously
described. The unwrapped phase is also to be expected. Additionally,
simulation shows that the SFR receiver works fine.




Figure 4. Shown here is the spectrum (A), magnitude of the waveform that reflects the random characters of the
target return, as well as the clutter property (B), frequency hopping in the received signal (C), and the unwrapped
phase (D) of a received SF radar signal measured at the receiver input.


The SFR waveforms resulting from the design in Figure 2 are
shown in Figure 5. Note that in the red waveform (the transmission
signal), the frequency content for each pulse is different. This is
because the frequency content increases with the timing. The
blue-colored waveform, the received RF signal, has a delay com-
pared to the transmitted signal and is being affected by clutter
and noise. The green-colored waveform is the demodulated signal.




Figure 5. Shown here are transmitted (red), received (blue) and demodulated (green) SFR waveforms.
06 | Keysight | Designing, Verifying and Testing Stepped Frequency Radar Systems for Commercial and A/D Applications - Application Note



Example: Simulating a SFR System (continued)
Using this high-resolution SFR design, two targets close to one
another can be easily detected (Figure 6). To detect the same
two targets using a pulse radar, the pulse width would have to be
increased at least 8 times, significantly increasing system cost.




Figure 6. The high-resolution SFR design was used to detect these two targets near one another




Figure 7. Shown here is a SFR receiver test signal generation for hardware
test.


Example: Testing a SFR System
Testing the SFR hardware receiver requires a SFR signal generator.
The received signal includes target returns with environments such
as ground clutter and noise.

Figure 7 shows the creation of a SFR test signal with two targets
near each other and clutter using SystemVue. The signal is down-
loaded into a vector signal generator (e.g., Keysight's ESG/MXG/
PSG Arb), via a vector signal generator link model, for upconversion
to RF frequencies. The generated test signal is verified using a
signal analyzer.
07 | Keysight | Designing, Verifying and Testing Stepped Frequency Radar Systems for Commercial and A/D Applications - Application Note



Example: Simulating a SFR System (continued)
In Figure 8, the received SFR signal is measured at the input of
the SFR receiver using a signal analyzer. Plot A shows the spec-
trum, while Plot B shows the waveform that reflects the random
characters of the target returns and clutter property. To observe
the frequency hopping in the received signal, look at the plot
frequency versus time (Plot C). In plot D, the unwrapped phase is
displayed.




Figure 8. Here, a generated SFR receiver test signal was measured by using Keysight's VSA software.

For SFR transmitter test, a SFR receiver (created in SystemVue) is
needed. Using a VSA link, the received waveform from the signal
analyzer is acquired and sent into the SystemVue SFR receiver for
demodulation, detection and recovery of the original target signals.
Figure 9 shows an actual software receiver that was created and
can be used to test real received SFR signals.




DUT




Figure 9. This test setup can be used for hardware test of the SFR transmitter and receiver.
08 | Keysight | Designing, Verifying and Testing Stepped Frequency Radar Systems for Commercial and A/D Applications - Application Note



Summary of Results
The low-cost, high range resolution SFR technique offers a
number of key advantages for non-destructive testing and
ground-searching applications in the commercial and A/D
industries. However, quickly and accurately developing SFR
systems requires a simulation-based solution.

The simulation platform presented here enables design, as well
as verification and test of SFR systems under different real-world
environments. SystemVue can provide both the software receiver
to test a customer's transmitter and the software transmitter to
test receiver components. Moreover, it provides the control and
automation that's critical for systems test. This capability, coupled
with the platform solution's flexibility and performance is key to
allowing today's engineers to develop effective SFR systems with
excellent real-world performance.


Related Information
SystemVue Radar application notes
http://literature.cdn.keysight.com/litweb/pdf/5990-5392EN.pdf
http://literature.cdn.keysight.com/litweb/pdf/5990-5393EN.pdf
http://literature.cdn.keysight.com/litweb/pdf/5990-6919EN.pdf
http://literature.cdn.keysight.com/litweb/pdf/5990-8349EN.pdf
http://literature.cdn.keysight.com/litweb/pdf/5990-7533EN.pdf
http://literature.cdn.keysight.com/litweb/pdf/5990-8556EN.pdf


SystemVue Radar product information
W1905 Web page: http://www.keysight.com/find/eesof-systemvue-radar-library
W1905 datasheet: http://literature.cdn.keysight.com/litweb/pdf/5990-6347EN.pdf
YouTube video: http://www.youtube.com/watch?v=97Px9ByNyMI
Webcast: "Uncovering the Hidden Impairments in Testing Advanced RADAR Systems"
09 | Keysight | Designing, Verifying and Testing Stepped Frequency Radar Systems for Commercial and A/D Applications - Application Note




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