Test and measurement tackling demand for higher frequencies and wider bandwidthStory
September 04, 2015
Just as software-defined radios (SDRs), signals-intelligence systems, radars, and sonars are challenged by reduced size, weight, and power constraints, so are the test and measurement systems used to ensure their effectiveness.
Modern radio architectures for military applications are driving the demand for higher frequencies, digital modulation, and wider bandwidths. Couple that with the push toward reduced size, weight, and power (SWaP), and you are adding tons of complexity to designs.
Test and measurement solutions have been following the industry on this ride by continuing via open industry-standard modular architecture and expanding software-defined architectures that enable “mission-specific channel, capacity, and range needs,” says Darren McCarthy, Marketing Manager for Rohde & Schwarz in Beaverton, Ore. “We have seen a steady increase in demand for high-performance products to support the different technology insertions. The test methodology incorporated to test individual radio waveforms is different than the efficient test methodology to test new software-defined radios. This creates a demand away from radio-specific testers to more general-purpose test and measurement equipment that is available as commercial off-the-shelf (COTS) to the broader radio industry.”
Common test assets define a universal test platform
As military systems add complexity they must also add flexibility to enable commonality, which reduces training and maintenance costs and speeds up product development. In other words, users want a universal test system.
“Radio frequencies (RF) and microwave instruments need to be flexible – to be upgradeable by simply substituting or adding a new module; to make new measurements just by downloading a new software application. This approach also keeps a lid on the costs of documentation, training, spares, and maintenance. Additionally, industry standardization promotes competition, ultimately improving performance at a reduced cost,” says Satish Dhanasekaran, General Manager, Mobile Broadband Operation, for Keysight Technologies in Santa Rosa, California.
“In both a development and manufacturing environment, for over a decade we have seen a continued effort from our customers to move from a radio-specific test architecture to a ‘universal test platform’ strategy,” McCarthy says. “Rather than developing and using radio-specific test platforms for each radio waveform, customers that need to combine the multiple technologies into a single radio are designing the radios and test platforms for testability with common test assets.”
Test assets range differently in each platform, “A software-defined radio can produce an unlimited number of radio waveforms. Let’s say the three different radio formats are planned to be fielded by a UHF radio for one customer using the same SDR,” he continues. “Each radio format has a different modulation type, bandwidth, and frequency.”
A good approach to the manufacturing process would be to use a Venn diagram, which according to McCarthy, is a good way to help customers understand the parameters needed during the process. Once that test platform is created, you can see the advantages of software-defined architecture that would fit in an atmosphere that changes to keep up with industry standards and new technologies. McCarthy’s company offers the Rohde & Schwarz SMW200, a vector-signal generator, and the R&S FSW, a signal and spectrum analyzer, used for both commercial radio and military tactical development and testing. (Figure 1.)
Figure 1: Pictured is the R&S SMW200 and R&S FSW, a vector signal generator and signal and spectrum analyzer, respectively. Photo courtesy of Rohde & Schwarz.
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Specifically, when a radio can produce unlimited number of waveforms, McCarthy says that “the production environment can be matured to focus on the test processes that actually focus on the variables expected to be found with tests rather than specific tests for each format. The modulation for one waveform might be ‘worst-case’ and be used as a proxy for other waveforms. It’s the same with all other in-band and out-of-band radio tests. This matured method of test is similar to how the commercial technologies (cell phones) have been tested for years. A full conformance test for a cell phone to a wireless standard might take a week, while the confidence testing in a manufacturing environment to assure that phone will pass might only take a few seconds.”
As the military moves away from more traditional standards of two-way radios to a network-based way of communications, the test and measurement industry follows right along. Technologies that are combined into a single radio design and a test platform is constructed with common assets; according to McCarthy, “it is safe to say that nearly 100 percent of top-tier radio manufacturers have moved in this direction or are in the process.”
GaN and PXI
Other technologies that drive RF test and measurement designs are PXI and gallium nitride (GaN), which also help enable cost-effective and efficient upgrades. “To address the simultaneous drivers of increase efficiency and improve spectral utilization, customers are driving designs for more efficient power architectures like envelope tracking with efficient new technology such as GaN,” McCarthy says. GaN helps fill the needs of military customers that are asking for higher frequency and higher power.
For its part, PXI permits flexibility in the manufacturing processes. Keysight Technologies’ M9451A PXIe Measurement Accelerator runs measurement FPGA algorithms, while in AXIe, the M8190A AWG has 5 GHz of bandwidth that provides testing on new radio formats and signal threats, Dhanasekaran says. “RF and microwave instruments need to be flexible – to be upgradeable by simply substituting or adding a new module; to make new measurements just by downloading a new software application. This approach also keeps a lid on the costs of documentation, training, spares, and maintenance. Additionally, industry standardization promotes competition, ultimately improving performance at a reduced cost,” he adds.
“In PXI, the M9381A Vector Signal Generator and M9391A Vector Signal Analyzer, as well as the fully configured EXM wireless device test set, provide as much as 160 MHz of RF modulation bandwidth. The M9290A CXA-m is a full-featured signal analyzer to 26 GHz with pre-amp and tracking generator in just four slots,” Dhanasekaran says. (Figure 2.)
Figure 2: The M9381A Vector Signal Generator provides frequency coverage from 1 MHz to 3 GHz or 6 GHz. Photo courtesy of Keysight.
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Another commercial technology driving designs is Voice over LTE (VoLTE), McCarthy notes. “It wasn’t until just last year, in early 2014, that VoLTE devices and networks enabled voice traffic on the LTE network. Future releases of the LTE standard, Rel 12 and 13, will feature device-to-device communication, higher power devices, and the ability to form ad hoc networks. These functions are essential for tactical or battlefield LTE networks,” says McCarthy.
“We have also seen a push to incorporate commercial technologies from LTE radios to automotive radar, which can be safely addressed by COTS test equipment,” says Keysight’s Dhanasekaran.
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