Wide-Bandwidth Requirements Push Test Capabilities to New Limits

Nov. 2, 2015
With wider bandwidths becoming more common in many applications, test equipment suppliers are providing advanced solutions to enable wideband signal generation and analysis.
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1. This test setup provides the capability to generate and analyze wideband millimeter-wave signals. (Courtesy of Rohde click image to enlarge)

Many of today’s applications, such as new wireless-networking standards, rely on wide-bandwidth signals. IEEE 802.11ac, for example, has greater bandwidth and can achieve much faster data rates than the previous IEEE 802.11n standard. In addition, applications like radar and electronic-warfare (EW) utilize wideband signals at microwave frequencies. Wideband radar signals provide several benefits, such as increased resistance to detection and jamming. In the future, 5G applications also promise to require wideband modulated signals—potentially at millimeter-wave frequencies.

To meet these demands, many of the latest test instruments have been developed to satisfy wide-bandwidth requirements for a number of applications. For example, today’s high-performance oscilloscopes have the capability to measure wideband signals at millimeter-wave frequencies. In addition, some manufacturers provide detailed descriptions of complete test setups that can be configured to perform wideband signal analysis.

IEEE 802.11 and 5G

The IEEE 802.11 wireless local-area-networking (WLAN) standard has been continuously updated to enable higher throughput. While IEEE 802.11n used a maximum channel bandwidth of 40 MHz, for example, the IEEE 802.11ac standard requires a mandatory 80-MHz channel bandwidth along with an optional channel bandwidth of 160 MHz. Thus, while the maximum theoretical data-rate for IEEE 802.11n is 600 Mb/s, IEEE 802.11ac can theoretically achieve a maximum data-rate of 6.93 Gb/s when using a 160-MHz bandwidth.

In addition to IEEE 802.11ac, the IEEE 802.11ad standard was created to enable WLAN operation in the 60-GHz band. The standard defines four channels that each has a bandwidth of 2.16 GHz. A modulation bandwidth of 1.76 GHz is used in single-carrier mode. IEEE 802.11ad can achieve peak data rates of approximately 7 Gb/s.

5G applications may also utilize millimeter-wave frequencies, as a significant amount of potential bandwidth is available in these frequency bands. Thus, future 5G applications will more than likely require wide-bandwidth signals. With the implementation of IEEE 802.11ad, as well as future 5G applications, it is essential that test equipment suppliers provide the capability to perform wideband measurements at millimeter-wave frequencies.

Generating and analyzing wider-bandwidth signals for IEEE 802.11ac applications can be challenging. Both 80- and 160-MHz bandwidth capabilities are needed to test components, transmitters, and receivers. A vector signal generator (VSG), such as the N5182B MXG from Keysight Technologies, can provide RF signals with a 160-MHz bandwidth. Another technique to create wideband digitally modulated signals is by using a wideband arbitrary waveform generator (AWG), such as Keysight’s 81180B, M8190A, or M9330A. The AWG can create the analog in-phase/quadrature (I/Q) signals, which are then applied to the external I/Q inputs of a VSG.

Signals with bandwidths as high as 160 MHz can be analyzed by using the 89600 vector-signal-analyzer (VSA) software combined with a signal analyzer, such as the N9030A PXA or the M9391A/M9393A VSAs. A digitizer or oscilloscope, such as the M9703A wideband digitizer or the Infiniium/InfiniiVision oscilloscope, can also be used in place of a signal analyzer. The M9703A, for example, can capture IEEE 802.11ac baseband I/Q signals as a result of its 800-MHz analysis bandwidth at full sampling rate.

2. These oscilloscopes offer test capability to 70 GHz along with a sampling rate of 200 GS/s. (Courtesy of Tektronix)

Test equipment suppliers are also providing solutions to analyze wideband signals at millimeter-wave frequencies. Such solutions are intended for applications like IEEE 802.11ad as well as upcoming 5G requirements. For example, Rohde & Schwarz offers a variety of test instruments to satisfy these demands. In fact, some of the company’s latest products can be incorporated into a complete setup that can be used for these applications (Fig. 1).

“Wide bandwidth is often discussed in conjunction with 5G. One also has to consider the frequency ranges of communication standards,” says Andreas Roessler, North American technology manager at Rohde & Schwarz. He adds: “Among the challenges associated with 5G are the increased capacity and significantly higher data rates in comparison with today’s networks. In addition, the industry has to move up in frequency to utilize the available bandwidth to 2 GHz and higher in the millimeter-wave space. Current discussions focus on 28, 39, 60, and 70 GHz.”

To further explain the test capability offered by Rohde & Schwarz, Roessler notes: “The analysis bandwidth of the FSW signal and spectrum-analyzer family has been extended to 2 GHz. In addition, the frequency range of the FSW has been extended to 85 GHz. For signal generation, the SMW vector signal generator now has a frequency range to 40 GHz, which can be further extended with the help of external mixers. Because of its integrated 2-GHz I/Q modulator, the SMW can provide modulated signals with bandwidths as high as 2 GHz when used with an external arbitrary waveform generator.”

Roessler continues, “In addition to extending the frequency range, Rohde & Schwarz has added a new measurement option that supports IEEE 802.11ad signal analysis. The IEEE 802.11ad standard is often mentioned when discussing 5G because it is the only wireless standard that already utilizes wider bandwidths to 2.16 GHz while operating in the 60-GHz frequency band.”

Wideband Pulsed-Radar Signals

Wide-bandwidth signals are also used in applications like modern radar systems. Such applications often use pulsed signals with wide bandwidths, which is important because ultra-wideband radars provide fine range resolution as well as increased resistance to detection and jamming. In addition, frequency-hopping transmitters operate over wide ranges. As a result, they require wideband signal capture for full characterization and to avoid missing hops. For their part, signal-intelligence (SIGINT) applications require the acquisition of wide contiguous bands to identify targets.

Test-equipment manufacturers are providing various means to analyze these wideband pulsed signals, such as high-performance oscilloscopes. Today’s oscilloscopes can analyze wideband signals at frequencies into the millimeter-wave band, which makes them ideal for applications like radar. For example, the DPO70000SX oscilloscopes from Tektronix provide users with measurement capability to 70 GHz (Fig. 2).

“A major problem with the test and analysis of ultra-wide-bandwidth signals is the need to configure and manage complex multi-instrument setups,” says Jim McGillivary, general manager of RF and component solutions at Tektronix. “In the real world, the fewer moving parts you have, the better off you will be. That’s a major benefit of a wide-capture solution based on a single high-performance oscilloscope, such as the 70-GHz DPO70000SX. With the integration of the SignalVu software, this solution provides the advantages of the scope’s signal fidelity and triggering capabilities coupled with RF analysis.”

Other solutions are available to analyze wideband signals for applications like radar and EW. Keysight’s Z9070B wideband signal analysis solution is one example, as it provides the capability to analyze signals with bandwidths to 1 GHz. Various Keysight test instruments are incorporated into the configuration to enable this capability.

As bandwidth requirements continue to increase, test equipment suppliers must provide the necessary test capability. Digital communications, radar, and EW are all applications that use wideband signals. With the emergence of IEEE 802.11ad along with potential 5G applications in the future, wideband signal analysis at millimeter-wave frequencies is also a requirement that needs to be fullfilled.

As a result, suppliers must offer enhanced performance capability to meet current and future requirements. High-performance oscilloscopes are already providing complete solutions to meet advanced demands. We can also expect to see suppliers offer signal analyzers with greater analysis bandwidth capability. In addition, test instruments will provide the means to generate wideband signals as requirements increase.  

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