Technical Innovations in the Keysight UXA Signal Analyzer

October 6, 2014

  1. Introduction
  2. Achieving Breakthrough Performance with Proprietary Converter Technologies
    1. Maintaining Excellent Dynamic Range with the Wide-Bandwidth ADC
    2. Improving Performance with the High-Speed, High-Resolution DAC
  3. Creating an Unprecedented Combination of Real-Time Bandwidth and POI
  4. Utilizing Real-Time Triggering, Gap-Free Recording, and Vector Signal Analysis
  5. Improving Productivity and Maintaining Compatibility with the Large Touchscreen
  6. Conclusion
  7. Related Information

Whether the application is in aerospace/defense (A/D) or commercial communications, engineers working on the leading edge need measurement instruments that provide headroom for next-generation requirements. That’s why we created the Keysight UXA signal analyzer. As the new flagship of our X-Series signal analyzers, the UXA leverages proprietary technologies to achieve new benchmarks in signal-analyzer performance.

The UXA enables analysis of today’s wideband systems by providing 510 MHz of instantaneous bandwidth, and up to 900 MHz bandwidth using the IF output. The standard instrument provides industry-leading performance in three key areas:

  • Lowest phase noise: Up to 20 dB better than the excellent Keysight PXA X-Series signal analyzer at 10 Hz offset, no phase noise pedestal
  • Best wideband spurious-free dynamic range (SFDR): greater than 75 dB over 510 MHz
  • Best wideband IF flatness: less than 0.7 dB over 510 MHz

For those who need even more performance, optional capabilities provide industry-leading performance with 510 MHz real-time bandwidth and 100% probability of intercept (POI) for signals with durations as short as 3.84 µs (detects elusive signals as short as 4.0 ns). The optional external atomic frequency reference provides exceptional long-term stability.

To enhance usability, the UXA provides a streamlined, touch-driven interface through a 14.1-inch display. By providing wider, deeper views of elusive and wideband signals—known and unknown—the UXA enables users to see more and take their designs farther.

Achieving Breakthrough Performance with Proprietary Converter Technologies

Progress in RF and microwave technologies is a complementary, back-and-forth process: new technologies lead to better tools, these lead to technology improvements, and the cycle repeats. In both A/D and wireless applications, bandwidths have been getting wider, and performance measures such as agility, sensitivity, and throughput have been constantly improving. To sustain the cycle of improvement, test equipment must keep up.

The latest iteration of the cycle has driven the development of the UXA signal analyzer, and key to several of its industry-leading performance figures are a new analog-to-digital converter (ADC) and a new digital-to-analog converter (DAC). Both are proprietary, Keysight-designed devices, optimized for RF and microwave applications such as radar, EW, and wireless.

Maintaining excellent dynamic range with the wide-bandwidth ADC

The ADC is an essential performance component within the UXA (Figure 1). It enables the 510 MHz IF bandwidth and delivers very low distortion.

Figure 1:

Figure 1: The wide bandwidth and very low distortion of the UXA is made possible by a proprietary Keysight ADC ASIC.

The ADC has been specifically designed for RF and microwave signal analysis, with a combination of sufficient bandwidth and low distortion that is ideal for optimizing today’s ultra-wideband systems. Using this technology, the UXA can maintain very high SFDR over its maximum 510 MHz instantaneous bandwidth, as shown in Figure 2

Figure 2:

Figure 2: The Keysight ADC in the UXA maintains high dynamic range over its full 510 MHz bandwidth. In this measurement, the largest spurious product is more than 88 dB below the level of the main signal.

In test equipment, performance headroom is essential to the design of operational systems. The dynamic range of the UXA is useful for design tasks such as evaluating the sensitivity of wideband EW equipment and tuning the operation of digital pre-distortion compensation in the latest multi-band or wideband wireless systems.

Of course, the ADC does not operate in isolation. To make the most of its performance, the UXA employs a new wideband RF front-end assembly with flatness of 0.7 dB over the full 510 MHz IF bandwidth. This exceptional flatness reduces the amount of amplitude correction necessary in the analyzer and minimizes any effect on the analyzer’s displayed noise floor.

Improving performance with the high-speed, high-resolution DAC

The importance of a wideband DAC in the performance of a signal analyzer is not as obvious as that of the ADC described above. However, the Keysight-proprietary DAC is no less essential to the fundamental performance improvements in the UXA.

As with the ADC, the RF-optimized DAC is designed to provide the performance headroom needed in test-equipment applications. The DAC offers an industry-leading combination of bandwidth and low spurious distortion. In the UXA, the DAC is the central component of a direct digital synthesizer (DDS), which complements the traditional PLL-based local oscillator (LO) used in spectrum and signal analyzers. The LO is used to perform frequency-conversion operations that bring the input signal to the proper IF frequency.

Because the LO is used in all frequency-conversion operations, its purity and frequency stability are reflected in the signal analyzer’s spurious and phase noise performance figures. In the UXA, the low spurious of the DDS-based LO translates into exceptional spurious performance in the analyzer, even with the UXA’s wide IF bandwidth.

The phase noise benefits of the DDS-based LO are equally impressive, especially at low and moderate carrier offsets, as shown in Figure 3.

Figure 3:

Figure 3: Compared with its high-performance predecessors, the UXA offers improved phase noise, especially at low and medium offsets. The use of a DDS-based LO is responsible for the majority of this improvement.

In the LO, a remarkable consequence of the switch from a PLL to a DDS architecture is the absence of a pedestal in the analyzer’s phase noise curve when the DDS is used by itself, without a PLL. The shape and corner frequency of a phase noise pedestal is governed by the PLL’s loop-filter characteristics, which are sometimes adjustable by the analyzer user as a way to optimize phase noise performance in the most important offset region for a measurement. In the UXA, the absence of a pedestal means that improved performance is available over a wide range of offsets up to about 1 MHz. For very wide offsets, a PLL is used along with the DDS to get a lower phase noise floor from the YIG-tuned oscillator. The PLL also provides loop filtering and avoidance of DDS spurs when necessary.

As with the ADC, the DAC and DDS-based LO do not operate in isolation, and the phase noise performance of the UXA is also the result of a new frequency-reference assembly. The design of the frequency reference has been optimized to take advantage of the DDS characteristics and improve phase noise performance, particularly for frequency offsets narrower than 100 Hz. As shown in Figure 3, phase noise at a 10 Hz offset may be as much as 20 dB better than that of the Keysight PXA, already an excellent performer in terms of phase noise.

Improvements in long-term stability can be obtained through the use of the optional atomic frequency reference. It provides extremely high stability for standalone applications in which a house standard is not practical.

Creating an Unprecedented Combination of Real-Time Bandwidth and POI

In the UXA, the 510 MHz instantaneous bandwidth is coupled to ultra-fast digital signal processing (DSP) to more than triple the widest real-time bandwidth currently available in a general-purpose signal analyzer. The analyzer’s full bandwidth is available for both real-time display and triggering operations, as shown in Figure 4.

Figure 4:

Figure 3: The 510 MHz instantaneous bandwidth of the UXA extends to real-time signal analysis, setting new benchmarks for real-time bandwidth and POI. The spectral density display is a powerful tool for finding fleeting or otherwise elusive signals and signal behaviors.

The UXA’s combination of DSP speed and bandwidth help it catch extremely brief signal events. It can detect elusive signals as short as 4 ns and provides 100% POI for signals with durations as short as 3.84 µs.

The fast DSP that provides real-time spectrum displays for the UXA also can be used to implement spectral and time-qualified triggers. As a result, the analyzer can distinguish between spectrally similar signals based on their time characteristics, and it can trigger on pulses shorter or longer than others. This capability could be used, for example, to find transient interferers in the middle of today’s dense wireless signal environments or to identify specific emitters in spectra from a battlefield.

The UXA’s density displays also can be extended beyond the 510 MHz maximum real-time bandwidth to provide the same views of signal behavior over much wider frequency spans.

Utilizing Real-Time Triggering, Gap-Free Recording, and Vector Signal Analysis

The full 510 MHz instantaneous bandwidth of the UXA is also available for use with the 89600 VSA software, either inside the analyzer or through a networked PC. Frequency-mask, time-qualified, and other real-time triggers can be configured to initiate individual measurements and gap-free signal captures for post-processing.

Because signals are captured in complete vector form, the post-processing can include changes to center frequency and span, with no need to capture new data. Many signals can be captured at once, typically including multiple frequency channels or bands. Individual signals can then be extracted from the capture for any type of analysis, including demodulation and time alignments or detection of cause and effect.

The VSA’s multi-measurement capability is expanded by the wide acquisition bandwidth of the UXA. Multiple, simultaneous demodulation measurements can be made from a single acquisition, covering different modulation types and bandwidths. Analysis can cover deliberately modulated signals, interferers, and other signal types such as radars, all at the same time.

Improving Productivity and Maintaining Compatibility with the Large Touchscreen

The UXA’s large capacitive display is touch-sensitive, responding to multi-touch inputs and gestures. Frequency spans and reference levels, for example, can be changed with a finger drag or pinch. Setup tabs provide easy access and quick switching between measurements.

The user interface and programming of the UXA are compatible with the rest of the X-Series signal analyzers, while the size and layout of the display bring most setup selections within two finger taps. Real-time measurements are especially intuitive with the touch interface.


The UXA X-Series signal analyzer is the latest iteration in the complementary, back-and-forth cycle of improvement that encompasses new technologies, new tools, and new developments. Built on Keysight-proprietary technology, the UXA delivers unsurpassed purity and clarity in signal analysis. The unprecedented quality of its IF section enables a designer to understand what’s happening inside their system and, ultimately, helps them prove that it’s meeting or exceeding its leading-edge performance goals.

About Keysight Technologies

Keysight is a global electronic measurement technology and market leader helping to transform its customers' measurement experience through innovation in wireless, modular, and software solutions. Keysight provides electronic measurement instruments and systems and related software, software design tools and services used in the design, development, manufacture, installation, deployment and operation of electronic equipment. Information about Keysight is available at

Related Information

Janet Smith, Americas
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