The progressive transformation of spectrum analyser technology

In technology, changes that occur over a long period of time are often based on a broad range of innovations. As a result, the actual extent of the transformation is clear only in retrospect. Such is the case with the evolution of spectrum and signal analysers.

The biggest changes are in the block diagram. Through the increasing performance of high-speed digitisers, digital filters and fast Fourier transform (FFT) technology, the intermediate frequency (IF) section has evolved from scalar to vector. Increasingly, this reflects the nature and architecture of the signals and systems many engineers must now measure.

The other important transformations are in the user interface (UI) and the user experience. Today, the touch-enabled UI technology widely used in smartphones, tablets and PCs can be readily adapted to the large displays that are increasingly common in signal analysers. Consequently, analysers now provide new levels of interaction that enable intuitive connections between cause and effect during development, debugging and troubleshooting.

Bending technology to suit the user

Over the past 20 years, changes in technology have driven departures from the familiar ‘swept spectrum analyser’ paradigm. The most significant were vector signal analysers (VSAs) in the early 1990s and, about 10 years later, benchtop real-time spectrum analysers (RTSAs).

These new instruments operated differently from traditional spectrum analysers, made different measurements and produced different displays. For some end users, the differences proved to be a substantial barrier.

Today, the technology in the latest Keysight X-Series signal analysers is designed to bend the trend in ways that make virtually every measurement task simpler and faster. This has been accomplished in two ways. First is the use of a single analyser to cover swept, vector and real-time signal analysis. From day to day, an RF engineer may need one or more of these capabilities.

Second is simplified measurement set-up and analyser operation in whichever mode the engineer chooses to use. With touch, access to rich functionality in measurement, display and analysis no longer requires a deep, complex hardkey/softkey UI.

Enabling accessible performance

Each X-Series signal analyser now has a large display with multitouch functionality similar to that of a tablet (36 cm diagonal in the UXA, 27 cm in the others). Measurement settings and displays are easily controlled using familiar gestures such as single or double tapping to select a parameter or expand a window, dragging and pinching to zoom and scale a display, and using press-and-hold to access context-sensitive selections.

The intuitive power of the swept-analyser paradigm remains. A single touch of an in-display menu panel, measurement bar, annotation hotspot or drop-down window provides direct access to major parameters whether the task is simple spectrum analysis or complex digital demodulation.

A single press on the menu panel provides direct access to capabilities such as Keysight’s Noise Floor Extension (NFE) technology, which yields an improvement of up to 12 dB in spectrum analysis noise floor.

In fact, it takes no more than two touches to complete most operations. This enables rapid navigation of display capabilities and analysis functions without abandoning the natural feel of a swept analyser when making basic spectrum measurements.

Shortening the learning curve

As signals and tests become increasingly complex, engineers often face a steep learning curve. In a signal analyser, there are two ways to mitigate this problem: minimise change from the familiar usage model, and use the same UI, measurement applications and programming commands across multiple measurement platforms.

There are five models in the X-Series: UXA, PXA, MXA, EXA and CXA. The shared internal architecture includes a measurement abstraction layer that, wherever possible, shields the front-panel user or instrument programmer from any internal hardware differences and complexities. With consistent operation and programming across the family, learning one X-Series analyser means knowing them all.

Finding problems, determining cause and effect

When used in VSA and RTSA modes, the large touch screen and multitrace displays make it easier for engineers to create multiple, simultaneous views of complex signals. These views leverage the engineer’s own knowledge and help them identify cause and effect even when signal behaviour is complex and timing relationships are unknown.

Drop-down windows enable quick configuration of an LTEA FDD ETC transmitter measurement, including 256QAM demodulation.

As with the UI, the five X-Series analysers share a variety of applications that are ready-to-use measurements for signal analysis. Examples range from parametric measurements such as phase noise and noise figure to standards-specific analysis of LTE/LTE-Advanced and W-CDMA. Across all five models, the use of consistent measurements, algorithms and controls produces repeatable results that reveal the performance of devices and designs.

The X-Series family is compatible with Keysight’s 89600 VSA software, which provides a comprehensive set of tools for demodulation and vector signal analysis. The software also provides connections to the simulation capabilities of electronic design automation (EDA) software such as Keysight’s ADS and SystemVue platforms.

Delivering better measurements

Recent advances in digital technologies have made their way into the local oscillator (LO) section of the X-Series signal analysers. Keysight designed and developed an RF-optimised digital-to-analog converter (DAC) which is the core of a direct digital synthesiser (DDS) that is used in the LO of the UXA and PXA models.

Because the LO is used in all frequency-conversion operations, its purity and stability are reflected in the spurious and phase noise specifications of both models. For medium and narrow frequency offsets, the DDS-LO is used alone. One key benefit is elimination of the typical pedestal that appears in the phase noise floor of analysers that rely solely on phase-locked loop (PLL) technology. For wider frequency offsets, the DDS-LO is used in conjunction with a YIG-based PLL to yield additional improvements in phase noise performance.

Preparing for future evolution

The digital technologies used in the X-Series signal analysers provide yet another useful benefit: future upgradeability. Initially, an engineer can select the level of performance and optional capabilities needed to match specific requirements such as frequency coverage, analysis bandwidth, phase noise and noise floor. As requirements change, additional or enhanced capabilities are easy to add. This type of future adaptability is an essential attribute of every tool an RF engineer chooses to use.

Top image: Keysight’s X-Series signal analysers.