Agilent's high-performance PXA signal analyzer adds real-time spectrum analysis capabilities

In the fields of aerospace, defense, and wireless communications, emerging challenges make system characterization and troubleshooting more difficult. Take radar and electronic warfare (EW) systems, for example, which are becoming more dynamic, faster, and cover larger spaces on the battlefield. This expansion of multi-standard, high-speed communication systems increases the probability of interoperability issues.

As signals become more complex and sensitive, gapless measurement technologies—real-time spectrum analysis and time capture—are gaining acceptance for mainstream applications. The Agilent PXA signal analyzer goes a step further by integrating these new capabilities into traditional signal analyzers, eliminating the need for users to purchase dedicated or single-purpose instruments. (Figure 1)

Figure 1. The Real-Time PXA is a cost-effective solution that allows you to identify spurious signals using traditional swept analysis and switch to real-time mode to observe pulsed spurious signals.

Agilent's real-time spectrum analysis (RTSA) is available as an upgrade option for new and existing PXAs, making the PXA the industry's first traditional signal analyzer that supports adding real-time analysis capabilities after purchase. This allows users to use real-time capabilities at one-tenth the price of a new real-time spectrum analyzer.

The RTSA enables users to see, capture and understand elusive signals on the lab bench or in the field. For deeper analysis, users can pair the real-time PXA with Agilent 89600 VSA software to fully characterize complex modulated signals.

Real-time analytics definition

Although different users understand "real-time analysis" differently, it contains a consistent core concept: for spectrum or signal analyzers with digital intermediate frequency (IF) sections, real-time operation processes all signal samples for a measurement result or trigger operation. (Figure 2) In most cases, the measurement result is a scalar quantity (such as power or amplitude) as opposed to a traditional spectrum measurement result.

Figure 2: Real-time operation occurs when the computation is fast enough to analyze the sampled data without gaps. In this case, the CALC operation includes the Fast Fourier Transform (FFT) calculation or power spectrum calculation, as well as the average calculation, display update, etc.

In addition to gap-free analysis, real-time RF analyzers have four key attributes: high-speed measurement, stable measurement speed, advanced composite display, and frequency mask trigger (FMT).

Typically, the spectrum stream during real-time processing is used for two purposes: the spectrum can be combined with a composite spectrum display or compared with a limit mask to perform a frequency mask test (FMT). The real-time PXA with option RTSA supports both functions.

Performing Real-Time Spectrum Analysis with the PXA

Like a dedicated real-time spectrum analyzer, the real-time PXA uses ASICs and FPGAs to convert sampled signal data into signal spectra at rates approaching 300,000 spectra/second. Spectral data is aggregated to build detailed displays such as density or histograms. Alternatively, the spectrum stream is sequentially tested against constraints and logic criteria to generate frequency mask triggers for specific spectra and specific behavior.

To enhance the performance of real-time spectrum analysis, the Agilent design team focused on four key aspects: bandwidth, dynamic range, probability of intercept (POI) and integrated analysis capabilities.

bandwidth

As the bandwidth and frequency bandwidth of the signals being analyzed become higher and higher, it is necessary for users to use higher bandwidth. The PXA with RTSA provides up to 160 MHz analysis bandwidth for real-time measurements, which is sufficient to cope with today's wideband signals and signal environments. Gapless bandwidth is not only suitable for real-time spectrum analysis, but also for FMT, gapless time capture, and real-time amplitude calculation of IF triggering.

Another key point: Unlike some similar products, the real-time PXA consistently collects gap-free data across bandwidths up to 160 MHz. Users can be confident that real-time mode will always capture detail on intermittent or rapidly changing signals.

Dynamic Range

The real-time PXA provides up to -75 dB of spurious-free dynamic range over a 160 MHz bandwidth, allowing the user to detect small, fast, infrequent signals in the presence of large signals. Dynamic range is enhanced by the PXA's low noise floor, and can be further enhanced when dealing with very small signals by adding the "Low Noise Path" option, which improves sensitivity while handling high-level signals. In all cases, the PXA's low noise floor enhances the ability to distinguish small signals from noise.

Probability of interception

POI is a key benchmark for real-time spectrum analysis. The real-time PXA can detect signals as low as 5.0 ns and as low as 3.57 µs with 100% probability of intercept (full amplitude accuracy). Gapless analysis is only part of POI. Other factors that affect instrument analysis performance include analyzer and processor dynamic range (including sensitivity), sampling bandwidth, processing continuity, and FFT overlap processing (for window function shape compensation).

Integrated analytical capabilities

In some cases, simply finding an infrequent signal is enough: just knowing that a signal exists, or finding the general shape of the spectrum, for example, is enough to answer questions, identify a problem, or suggest a solution. In other cases, finding an infrequent signal is only the first step in solving a problem in a system or signal environment.

Using VSA software in conjunction with the real-time PXA, signals acquired in real-time mode can be fully analyzed and demodulated. In addition, real-time FMT can focus the full measurement capabilities of the VSA, including demodulation and time capture (Figure 3), on hard-to-find signals. This is particularly useful when measuring modulation transients, frequency hopping, frequency settling, and unintentional transients in signal sources such as voltage-controlled oscillators (VCOs).

Figure 3. FMT can be used to capture transient events in real time. Vector signal analysis provides multiple views, showing details such as a time-gated spectrum (top) and simultaneous display of the power envelope (blue) and time waveform (green).

Get the most out of signals acquired in real-time mode

There are two additional features you need to pay attention to: histogram/density display and frequency mask triggering.

Histogram or density display

Real-time spectrum analyzers can generate thousands of spectra per second to capture the dynamics of frequency-agile or fleeting signals. Such high-speed signals are beyond the resolution of the human eye, making it necessary to display a large number of measurement data in a single display trace. A real-time PXA can generate nearly 300,000 spectra per second. However, most people can only see 30 spectra. To best observe real-time measurement results, approximately 10,000 results should be displayed for each display update. [page]

A real-time analyzer builds an informative display by compiling statistics and showing how often a particular measurement occurs (e.g., a particular amplitude at a particular frequency). The measurement result histogram is an enhanced spectral measurement feature that shows the frequency of measurement occurrence. Some might view this as a crude expression of probability.

The display is color or intensity coded. As old data disappears, persistence functions can be added to focus on recent events. Trace data (most recent display update or average) is overlaid to produce a trace that looks similar to a traditional spectrum measurement.

This approach helps engineers see and focus on infrequent or transient events and distinguish them from other events. By changing the persistence and weighting values ​​or schemes, specific events can be highlighted. Real-time PXA provides full trace cursor capabilities for the persistence display, supporting the user to interpret and analyze the measurement results.

FMT Technology and Applications

When looking at a specific signal, FMT can compare a high-speed data stream to a user-defined spectrum mask. A trigger is generated when the mask range is exceeded or the signal enters the mask area. Conditional triggering can be performed on a signal when it enters or re-enters the mask area. This feature is particularly useful for conditional triggering on situations such as when a signal leaves the mask or re-enters the mask.

In real-time PXA, the template consists of upper and lower limits and can be entered numerically or graphically. The analyzer automatically generates a template using the measurement signal environment, allowing the user to modify it as needed, saving measurement time. To simplify this process, the template is displayed simultaneously with the real-time measurement trace.

FMT can be used to generate relatively frequent continuous triggers. In contrast, one of the most powerful uses of FMT is to measure behavioral events that occur very sporadically, with intervals of minutes or even hours. With VSA software, pre-trigger and post-trigger delay functions can capture the start and end of an event, or any signal between two time points.

Improve the utilization of common tools

The current economic climate has put more pressure on most companies to maximize the effectiveness of existing equipment such as traditional signal analyzers. On the other hand, strict spending controls have made it more difficult to justify replacing single-purpose tools (such as dedicated real-time analyzers).

This is one of the main reasons why Agilent has worked hard to develop the RTSA upgrade option, which can be added to new or existing PXA signal analyzers. It is also the reason why the PXA is designed from the beginning to support the addition of functions such as RTSA. As a result, Agilent provides users with a comprehensive instrument that combines traditional functions and real-time analysis functions, providing consistent performance regardless of which mode is used.