Elaborating on the design, prototyping, and test of radar

The Test Applications Special Report in our April print issue describes how modern complex radar systems with wide bandwidths present significant test challenges. You'll find the complete report online here. In addition, industry experts have elaborated on various aspects surrounding radar test—including issues relating to software, design, prototyping, spectrum crowding, instrument modularity, pulse measurements, test simulation, multi-element radar, and slow-moving targets—as described in this Web-exclusive companion article. You'll also find links to relevant white papers, articles, application notes, webcasts, and videos.

Design and prototyping

Phyllis Cosentino, product marketing manager for RF & wireless test at National Instruments, described radar design and prototyping as well as test. She noted that NI works with various partners. “For example,” she said, “our NI partner RADX offers optimized solutions for deployment on National Instruments PXI/PXI Express-based modular systems. RADX combines its patented and patent-pending real-time spectrum and high-bandwidth time-domain analysis software with NI modular instrumentation, NI Phase Matrix high-speed RF memories, and next-gen arbitrary waveform generation subsystems to deliver unprecedented performance, functionality, and value for radar test and measurement.”

Cosentino also commented on NI offerings beyond radar test applications. “In addition to radar test,” she said, “National Instruments offers a wide range of tools. NI tools can be used for radar design and prototyping.”

She added, “The issue of crowded spectrum provides a challenge in the design and tests stages—particularly in being able to simulate the appropriate interference.” National Instruments, she said, provides design tools that allow you to prototype a complete radar system using the NI LabVIEW graphical system design environment—including everything from pulse generation to range detection analysis.

“LabVIEW allows you to readily connect your algorithms to radio hardware so not only can you simulate and prototype your system in LabVIEW and NI AWR VSS, but you can also test this configuration with real hardware,” she said.

Another feature National Instrument customers use to deal with spectrum-crowding problems is the record and playback capability. “Customers will take an NI signal analyzer into a field condition (particularly a known-difficult environment), connect it to an antenna, and then physically record all of the spectrum conditions as they occur in real time to disk,” she said. Once recorded to disk, this information can be played back at a wide range of RF frequencies to test their radar products under simulated conditions.

Cosentino concluded, “In addition to the ability to prototype algorithms in LabVIEW, LabVIEW also connects to the NI AWR VSS tool and NI AWR Microwave Office tool. This allows you to measure the effect of circuit design on the performance of the radar. So in addition to testing the algorithm, you can actually test how the behavior of various components within the transmitter/receiver chain will influence the overall receiver result.”

Benefits of modularity

Mark Prichard, business development technologist at Aeroflex Test Solutions, elaborated on modularity. “Because of the modular nature of the Aeroflex solution, hardware and software elements can be easily replaced as new technology becomes available,” he said. “In general physical parameters (bandwidth and agility) of radar signals have a lower rate of change versus the content (modulation). The analysis methods employed by the Aeroflex instrumentation are software-based; as new analysis techniques are developed, these are added to the instruments as software upgrades.”

Prichard also commented on how customers can assure the performance of their radar systems in a spectrum crowded with commercial and other RF/microwave signals. “The broadband nature of Aeroflex instruments coupled with deep memory recording allows for the full time correlation with signal content to be analyzed for spectral areas of interest,” he said. Automatic modulation recognition as well a full-time domain analysis can be used to determine the characteristics of all signals in a spectral area of interest.” He added that the Aeroflex instruments can also be used for long-term monitoring operations of spectral occupancy, which can be used to understand the effects of incursions into a spectral space.

“The Aeroflex solutions are designed for field and laboratory use,” he added. “The design of the instrument, modular in hardware and software, provides operational capability in the research, development as well as validation/verification fields.”

Evolving pulse-measurement requirements

Bob Buxton, manager of product marketing, microwave bench-top products at Anritsu, described the shortcomings of conventional pulse measurements. “Conventional pulse measurements have become obsolete when analyzing these next-generation radar systems.” He listed a variety of reasons:

Existing pulse-test methodologies require trade-offs to be made based on required duty cycle, pulse width, dynamic range, and more.
Whether engineers track high-speed targets or detect slow, low, and small objects, better analysis tools are needed.
In some applications, observing behavior over longer periods of time (without sacrificing resolution) may be important, whether it's looking for thermal and trapping effects in devices or measuring DUTs with lower pulse repetition frequencies.
Ensuring proper measurement setup and timing alignment can be difficult, especially when measurement solutions require the user to toggle between setup and measurement screens.
Calibration under pulsed conditions adds an extra degree of challenge.
Timing and synchronization issues create uncertainty and can include unwanted behaviors.

Buxton said, “The Anritsu VectorStar MS4640B series of VNAs equipped with Option 035 IF Digitizer and Option 042 PulseView addresses these challenges with a number of industry-firsts to deliver confidence on the cutting-edge.”

He added, “The digital IF acquisition system has 200 MHz of bandwidth for enhanced resolutions as fine as 2.5 ns and more accurate time referencing. The architecture also capitalizes on deep memory of up to 0.5 s to observe DUT behavior over longer periods of time without sacrificing resolution. The VNA platform's four independent receiver measurement windows enable reference position control to support various calibration and system timing needs, which may otherwise mask DUT rise/fall behavior.”

As for contending with a crowded spectrum, Buxton said, “The Anritsu MG3710A and MG369x series can generate commercial and/or other radar signals to create simulated real-world 'electronic environments.' Creating these scenarios allows engineers to accurately test their radar designs to ensure they will perform in today's crowded spectrums.”

Anritsu also offers solutions for radar test outside the MIL/aero area. “For measurement in the automotive radar frequencies of 77 GHz,” Buxton said, “Anritsu has developed unique performance capabilities utilizing the VectorStar ME7838A millimeter-wave (mm-wave) system with the Anritsu-patented model 3743A frequency-extension modules. The modules offer superior dynamic range and noise floor compared to traditional mm-wave modules. They also offer excellent calibration stability, significantly reducing the number of calibrations required during a production run. The compact size of the module, 1/50th the volume of traditional mm-wave modules, allows mounting on smaller probe stations and reduces capital equipment investments.”

Test scenario simulation

Richard Duvall, technical marketing manager at Tektronix, described a test-scenario simulation of a full range of radar signals. Simulation, in a test scenario, of the full range of radar signals requires these steps:

Create single- or multiple-pulse groups to form a coherent or non-coherent pulse train.
Define each pulse group independently or add different pulse groups to simulate simultaneous multiple target returns.
Define inter- and intra-pulse-hopping patterns in both frequency and amplitude.
Define all pulse parameters including start time, rise time, off time, fall time, pulse width, droop, overshoot, and ripple.
Define a staggered PRI with ramp and user-defined profiles and add up to 10 different multipaths.
Provide support for a variety of intramodulation types such as FM Chirp, QPSK, BPSK, FM Step, and Barker/Frank/Polyphase codes, including P1/P2/P3/P4, user-defined Step FM/AM, Step PM/AM, and custom modulation.
Define antenna-beam profile and simulate target returns.

He added, “Monitoring the intended signals emanating from a radar system may be necessary to assure compliance with regulations as well as to confirm interoperability when multiple systems are installed in close proximity to each other.” With multiple pulses included in one waveform, he said, it's not easy to see the differences between the individual pulses. “If there are differences, they are more subtle than can be seen from a voltage waveform,” he explained. “The SignalVu vector-signal-analysis software uses the digitized voltage waveform stored in the oscilloscope to make all of the RF measurements. A pulse table with basic timing and amplitude measurements can identify individual pulses and average power. By using the FFT mode instead of the trend mode, periodic disturbances that are well below the AVG power levels from external systems can be identified.”

Duvall also commented on examining an installed radar system: “One important task is to check for emissions that do not help the radar and very well may cause interference.” It's important to consider spectrum allocations as well as other nearby RF equipment and facilities, he said, adding, “Unintended signals may also provide increased visibility of radar, or an unwanted signature that can be used to identify the radar. There may be signals radiated from a radar system that will create interference to other systems. These may be at frequencies outside the assigned channel of the main radar transmitter signal. Some of these signals may be active all the time, and some may be active only during pulse transmission. This requires stepping across the entire frequency range of the analyzer.”

He elaborated: “Some signals may only be present during the pulse, but be on a different frequency. Some signals may be completely unrelated to the pulse, and may be on any frequency including within the pulse frequency itself. To discover signals such as these, a monitor is needed which is continuous and also one that can show a single signal deviation out of the continuous examination.” The DPX Live RF Spectrum Display can provide the necessary monitoring, he said.

Finding interfering signals

Greg Jue and John Hansen, Agilent application engineers, commented on finding and identifying interfering signals. “Spectrum is becoming increasingly complex,” they said, “with many potential sources of interference. Several challenges include testing receiver robustness in complex emitter environments and finding and identifying interfering signals in a crowded spectrum.”

They added, “For evaluating hardware in the R&D lab environment, Agilent offers multi-emitter solutions that combine design simulation software with a precision arbitrary waveform generator (AWG). Agilent SystemVue electronic system-level (ESL) software can be used to create a variety of emitters: radar, wireless communications, and wireless connectivity. The resulting signal scenarios can be downloaded to and played back with Agilent's 12-GS/s M8190A precision AWG. Understanding a crowded spectrum and finding interfering signals is made easier with Agilent's real-time spectrum analysis (RTSA) capability with frequency-mask triggering (FMT). This is a 'high probability of intercept' analysis mode that finds and displays unknown signals within a 160-MHz bandwidth. This mode can be added to existing X-series signal analyzers. For a deeper understanding of complex signals and environments, the RTSA and FMT can be combined with Agilent 89600 VSA software for short recordings and comprehensive demodulation and vector signal analysis.”

Challenges of AESA radar

Darren McCarthy, a technical marketing manager at Rohde & Schwarz, also elaborated on radar test. “There are two major trends in radar: the use of Active Electronically Scanned Array (AESA) radar, and the application of using radars on slower moving targets (walking),” he said. “Multi-element AESA radars offer a challenge to the test time required to validate the manufacturing performance needs. Typically, these antennas can have up to 5,000 elements, making test throughput a major design criterion. When you consider the practical aspects of testing the T/R modules in an AESA radar, the R&S TS6710 using the high-performance R&S ZVA network analyzer provides the most efficient testing of the necessary parameters over the broad frequencies of operation.”

He added, “For measuring the Doppler of slow moving targets, the performance of the close-in phase noise is an essential consideration in the selection of a signal generator and analyzer. As a major contributor the residual pulse-to-pulse phase performance measurement, the R&S FSW has the industry-leading performance phase noise of any commercially available spectrum/signal analyzer.”