Demand for test solutions in the communications and wireless sector continues to soar. Not only has there been an explosion in the adoption rate of new wireless technologies, but couple that with tough standards, multiple radios per product, and millions of devices to test, and it quickly becomes evident that testing capability is critical to the success of any wireless device today.
Not to fret, though. Test and measurement companies are on top of the situation. A steady stream of new equipment and software continues to flow into the hands of engineers to help test almost any wireless product.
WI-FI TESTING David Hall, National Instruments’ RF & communications product manager, thinks that the two most influential factors impacting new test equipment are systems-on-a-chip (SoCs) and the need for shorter test times.The latest wireless SoCs put a complete transceiver and all ancillary circuits on a chip. In fact, it’s common to see multiple radios per chip. Just look at the combo chips that put Wi-Fi, Bluetooth, GPS, and an FM radio, or some combination thereof, on a single chip for advanced cell phones. How does one test that chip after it’s manufactured and in the handset?
Second, with fewer circuits in a product, the cost of that product is being influenced more and more by the amount of time needed to test it. Test time has grown to be a greater percentage of the cost than the bill of materials (BOM) in some products. Hall says NI is helping to solve these problems with its software-defined approach.
NI’s Wi-Fi wireless local-area networking (WLAN) test solution can generate and analyze RF signal measurements four times faster than other modular instrumentation solutions and up to 10 times faster than traditional box instruments. It combines the NI WLAN Measurement Suite software for the LabVIEW and LabWindows/CVI development environment with the NI 6.6-GHz PXI Express RF hardware to deliver increased speed and flexibility for testing IEEE 802.11a/b/g standards.
Because this solution is software-defined, engineers can easily configure the same measurement hardware to test more than six other RF communications standards, including Bluetooth, GPS, RFID, and WiMAX. It comprises the NI PXIe-5663 6.6-GHz RF vector signal analyzer, the PXIe-5673 6.6-GHz vector signal generator, the PXIe-1075 18-slot chassis, and the PXIe-8106 dual core controller (Fig. 1).
The software component consists of the NI WLAN Generation Toolkit and the WLAN Analysis Toolkit. Both come with several example programs to help you get started quickly with automated test applications. Physical-layer (PHY) measurements like power, error vector magnitude (EVM), and spectrum mask margin can be made up to 10 times faster than available alternative measurement solutions. For example, an EVM measurement can be done in as little as 8 ms.
LTE TESTING Perhaps the hottest area in wireless test is equipment and software for testing Long-Term Evolution (LTE) 4G cellular products. Basestation and handset manufacturers are now making the products for LTE, which may show up as early as next year. LTE is a complex wireless technology that requires leading-edge test equipment to ensure compliance with the new 3GPP standard as well as country regulatory requirements.Anritsu showed off a promising LTE tester at April’s International CTIA Wireless conference in Las Vegas. It won second place in the 4G Service Creation & Development category of the show’s E-Tech Awards. The MD8430A Signalling Tester, an LTE basestation simulator, is designed for users who need to test wireless LTE chips and mobile end products like handsets (Fig. 2).
Thanks to the MD8430A’s four RF units, it can be used for 2x2 multiple-input multiple-output (MIMO) testing, including system handover tests in a simulated network environment. The simulator can conduct end-to-end testing at downlink speeds up to 100 Mbits/s and uplink speeds to 50 Mbits/s.
All critical 3GPP air interface LTE protocol tests are supported, including baseband coding/decoding; processing tests; protocol sequence tests such as position registration, origination, termination, handover, terminal, and network disconnect tests; and applications tests. L1 and L2 cache analysis functions are also provided. Moreover, the unit supports handover tests with UTRAN/GERAN systems.
The MD8430A can be integrated with Anritsu’s MD8480C WCDMA Signal l ing Tes ter to simulate both WCDMA and HSPA (up to release 7) and GSM/ GPRS/EGPRS basestations. It’s also usable with the company’s Protocol Test System and Rapid Test Designer.
MIMO TESTING While LTE testing is complex, it intensifies further when MIMO antenna technology is added to the mix. MIMO testing often requires multiple pieces of equipment. One of the best ways to test the MIMO capability of a device is to use a channel emulator, which is a box of hardware and software that acts like the wireless path through the ether itself.Channel emulators can be programmed to simulate the noise, spatial differences, attenuation, multipath, and other characteristics that vary during a connection. One of the companies specializing in MIMO channel emulation, Azimuth Systems, is known for its Wi-Fi and WiMAX emulators. Yet its ACE MX MIMO system uses all of LTE’s features with orthogonal frequency-division multiplexing (OFDM) and MIMO for testing LTE products (Fig. 3).
Continue to page 2
Key features include MIMO channel emulation to test multiantenna functions like spatial streaming, TX and TX diversity, collaborative uplink, and multicast/broadcast under diverse RF conditions. The emulator possesses superior RF performance such as noise floor, EVM, and signal-to-noise ratio (SNR) to provide error-free conformance and performance testing from 450 MHz to 5.9 GHz.
The ACE MX’s dynamically programmable parameters include propagation delay, output power, Doppler shift with wide ranges, and many pre-programmed standard channel models (3GPP, 3GPP2, ITU, SCME). Its rapidly configurable combinations of test configurations range from 1x1 single-input single-output (SISO) to 8x4 MIMO, all of which can be unidirectional or bidirectional.
Completely self-contained, the ACE MX also features bidirectional channel emulators including circulators, attenuators, adaptive white Gaussian noise (AWGN), and selfcalibration. Finally, it uses a simple graphic interface and automation application programming interface (API) with five simple steps from power up to operation. Users can perform channel model control, scanning, fast forward, rewind, and looping.
The ACE MX provides all of the backward-compatible channel emulation features that are required for the related 2G and 3G cellular products. Handoffs or “hand downs” will be common when LTE is used. That’s because products will need to shift gears to previous technologies like WCDMA or GSM if the channel isn’t sufficient to handle LTE or if LTE just isn’t available.
MICROWAVE TESTING As wireless components and equipment continue to move up in the spectrum, testing becomes even more challenging. But again, test companies are keeping pace. Agilent has just added some products that make aerospace, defense, and other wireless microwave equipment testing faster and easier.For example, the PNA-X is Agilent’s non-linear vector network analyzer (NVNA). The original unit, introduced back in 2007, had an upper frequency limit of 26.5 GHz. Its latest versions offer frequency coverage limits to 13.5, 43.5, and 50 GHz. All of the PNA-X models are designed to test both passive components (transistors, cables, printed-circuit boards, filters, duplexers, and backplanes), active devices and circuits (amplifiers, mixers), ICs, modules, and other subassemblies (Fig. 4).
The PNA-X’s configurable two- or four-port analyzer offers a single-connection, multiple-measurement approach for continuous- wave (CW) and pulsed S-parameters, compression, intermodulation (IMD), and noise figure measurement. It also has two built-in signal sources with high output power (+16 dBm), low harmonics (–60 dBc), and a wide power sweep range (40 dB).
Other measurements include vector noise figure, gain compression true and differential, and nonlinear vector network analysis. The internal signal routing switches simplify the change for one test setup to another with little or no additional equipment. Internal pulse modulators and generators are included to simplify and speed up measurements.
The 13.5-GHz model is designed to meet the needs of a wide range of wireless communications products where reduced test time, number of test stations, and test cost are critical. Multiple stations are often needed to complete the testing on a product, such as a low-noise amplifier (LNA) where gain, match, distortion, and noise figure must be measured. The PNA-X can perform all of these tests with a single connection and reduce the number of test stations by as much as 75% or cost by 30%.
The 43.5- and 50-GHz models target radar, satellite, and electronic warfare (EW) applications that usually require complex test systems with multiple racks of many instruments. Because so many test functions are already built into the PNA-X, it’s possible to reduce equipment count by 50% and increase throughput by 400%. Using the NVNA, you can make S- and X-parameter measurements and then use them with Agilent’s Advanced Design System to simulate actual linear and nonlinear component behavior.
Designed to improve some aspects of microwave testing, Agilent’s PSG E8257D signal generator option 521 has a frequency range of 250 MHz to 20 GHz (Fig. 5). The big news, however, is that this generator breaks the 1-W (+30 dBm) output power barrier. This feature alone helps eliminate extra amplifiers, couplers, and detectors.
Most generators in this frequency range deliver less than +25 dBm, yet some applications require more power for proper testing, like traveling wave tube (TWT) testing and automatic-test-equipment (ATE)/ antenna test configurations. In many test setups with multiple cables, filters, switches, couplers, and so on, these interconnecting devices introduce significant attenuation that often must be compensated for with an external amplifier.
Also, the PSG E8257D’s adjustable RF output power hardware clamp can protect sensitive devices under test from excessive power exposure. It can be varied over the +15- to +33-dBm range.
Microwave testing often needs even higher power. The Giga-tronics GT-1000A linear amplifier provides up to 40 dBm (10 W) of output power from 2 to 20 GHz (Fig. 6). Some of the many applications include wireless communications, electromagnetic compatibility/electromagnetic interference (EMC/EMI), defense EW, radio-frequency IC (RFIC) and monolithic microwave IC (MMIC) testing, basestations, radar, and satellites.
The GT-1000A also makes a good ATE building block. The output power is typically 5 to 7 W in the 8- to 20-GHz range. Maximum load voltage standing-wave ratio (VSWR) is 3:1, and the harmonic distortion is less than 30 dBc typical.
Continue to page 3
SPECTRUM ANALYSIS Spectrum analysis is still the backbone of most wireless tests. You get that feature in a vector signal analyzer (VSA), but a straight spectrum analyzer often offers features that can do more for your particular application. A particularly intriguing new device is Tektronix’s enhanced RSA6000 real-time spectrum analyzer (Fig. 7).The 14-GHz RSA6000 was first introduced in 2006. Besides a bandwidth of 110 MHz, it featured Tektronix’s Digital Phosphor (DPX) technology. This display technique color-codes the display with intensity grading, selectable color schemes, and statistical traces to communicate more information in less time.
With DPX technology, you can see multiple signals sharing the same frequency at different times, not just the largest, smallest, or average levels as you would see on a conventional spectrum analyzer. You also can see signal details that are completely missed by conventional spectrum analyzers and VSAs. This leads to faster and more thorough troubleshooting and debugging.
Tektronix essentially reinvented the RSA6000 by improving its specifications and adding features. The new model captures 292,969 spectrums per second—up from the original model’s 48,000 spectrums per second—so you can capture very short duration transients missed by other conventional spectrum analyzers. Such a feature is especially helpful when testing software-defined radios and radar.
You can also perform a sweep across the full input range from 9 kHz to 14 GHz. The RSA6000 collects hundreds of thousands of spectrums per second in 110-MHz chunks, which greatly enhances the reliability in capturing time-interleaved and transient signals.
The RSA6000’s DPX Density trigger enables triggering on signals within other signals. With it, low-level random events are isolated faster and easier. Other enhancements include the new time-domain triggering, which adds a runt trigger and the ability to time-qualify any trigger. These trigger features are ideal for radar, EW, and spectrum-management testing.
Wireless design, research, development, and production test engineers in military communications, satellite test, radar, portable mobile radio (PMR) test, and other applications can take advantage of Aeroflex’s 3250 series. The family comprises four models, each measuring a range beginning at 1 kHz, with the 3251 ranging up to 3 GHz, the 3252 to 8 GHz, the 3253 to 13.2 GHz, and the 3254 to 26.5 GHz.
Each model includes a Windows XP operating system, remote-control capabilities via a LAN, general-purpose interface bus (GPIB), and RS-232C, in addition to a 7-in. touchpanel screen, which makes them easy to operate with exceptional connectivity, according to Aeroflex. The display provides an ample viewing area so data can be seen easily, even in split-screen mode or with multiple windows open. Three traces can be displayed per window, and as many as nine markers can be selected with a marker table viewable in an alternate window.
Al so, the ser ies includes digi tal demodulation capabilities for the analysis of 802.11a, b, and g wireless networks, enabling engineers to analyze the transmitter characteristics of wireless devices. Optional measurement personalities include GSM/EDGE, WCDMA, WiMAX, and WLAN, as well as electromagnetic compatibility (EMC) pre-compliance test.
Built-in functions simplify the evaluation of many common measurements, including channel and multi-channel power, pulsed measurement, gated sweep, occupied bandwidth, spectrum emission mask, third-order intercept (TOI) measurement, total harmonic distortion, AM/FM and digital demodulation analysis, X-dB down, and phase-noise measurement.
The 3250 devices offer local-oscillator (LO) of –115 dBc/Hz and a display average noise level (DANL) of –145 dBm/Hz. They also incorporate 30-MHz I/Q demodulation bandwidth and a removable hard disk as standard. The software provides a GUI within the spectrum analyzer menus to display the required suite of user-selectable parameters. These high-performance, portable spectrum analyzers range from 24 to 20 lb.
ATE TESTING One of the most critical components in automated test systems for wireless is the switch needed to select inputs, outputs, and miscellaneous connections for various tests. They must be fast, transparent, and able to work at the highest frequencies. Peregrine Semiconductors’ PE42552 SPDT 50- RF switch fits that set of requirements (Fig. 8).The device is designed with the company’s HaRP-enhanced UltraCMOS siliconon- sapphire process technology. It covers from 9 kHz to 7.5 GHz without gate lag and phase drift, and it has a fast switch settling time. This CMOS switch also features an isolation of 47 dB at 3 GHz and about 30 dB at 7.5 GHz.
Another frequently sought ATE component is the attenuator. Peregrine’s PE43703 is a 7-bit digital step attenuator (DSA) with a three-wire interface bus. The attenuation range is 31.75 GHz in steps of 0.25, 0.5, and 1.0 dB. The DSAs operate from dc to 6 GHz and have an attenuation accuracy of ±0.2 = 2% at 3 GHz with an insertion loss of 1.6 dB. Its third-order intercept point (IP3) is +57 dBm. The DSA is a good companion for the PE42552 switch.