Capture Fast and Agile Frequency Hopping Pulses

Overview

Electronic warfare (EW) often resembles a high-stakes game of cat and mouse. Adversaries seize opportunities and vulnerabilities in the electromagnetic environment using jamming and deceiving techniques while defense units aim to locate, intercept, and neutralize these threats. Researchers and defense agencies must stay ahead of these threats using cutting-edge science and pioneering technology. Continuous innovation in EW is critical for national safety and security.

Keysight collaborated with a European defense agency specializing in solutions to solve defense and security challenges, both safeguarding its homeland and supporting its allies. The agency aims to help the national defense department in implementing robust security recommendations. By partnering with industry and academia locally and internationally, the agency fortifies this approach to tackling physical and electronic threats, whether originating internally or externally.

Challenges

One of the defense agency’s labs focuses on communications, radar, threat analysis, and EW. The lab is always on the lookout for new and emerging EW threats. A typical challenge involves adversaries attempting to jam and disrupt signal transmissions, jeopardizing national security and safety.

Undoubtedly, the number of threats and their sophistication will grow as technology improves and becomes more widely available. At the same time, frequency-hopping techniques and emitter technologies are evolving in complexity. When characterizing new and emerging emitters, analysts face the challenge of acquiring fast and agile frequency-hopping pulses that may have narrow bandwidths on an individual basis. They also seek insights into the speed and patterns of pulse hopping.

With increasing communication systems’ bandwidth and frequencies, there is a pressing need for an ultrawide bandwidth acquisition system that covers the portion of the entire electromagnetic spectrum of interest. The system must have sufficient dynamic range to capture even small signals. Given the complex nature of the pulses and the large volume of acquired measurement data, analysts need specialized software to efficiently classify signals and perform pulse analyses.

Solutions

Keysight addressed the customer’s challenges by deploying cutting-edge hardware and software. Specifically, the real-time spectrum analysis (RTSA) MXR oscilloscope paired with the PathWave Vector Signal Analysis (VSA) software, as depicted in Figure 1.

The MXR oscilloscope can sample up to 16 GSa/s across its four channels, with 6 GHz bandwidth. For more demanding radar and EW pulse signal analyses, Keysight offers the UXR oscilloscope, which provides an impressive sampling rate of up to 256 GSa/s across 4 channels and a bandwidth of 110 GHz. Both the MXR and UXR oscilloscopes have a 10-bit analog-to-digital converter (ADC), up to 9 effective number of bits (ENOB), and digital down conversion (DDC) to enable fast measurement and wide dynamic range. These tools are necessary to achieve accurate characterization of sophisticated emitters. They also enable the simultaneous viewing of multiple radio signals with the coherent multi-channel capability and integrated real-time spectrum analysis (RTSA) option.

A high sample rate also means high memory usage to store a high volume of data. Unlike the MXR, the higher-performance UXR offers variable-length segmented capture (VLSC) and real-time DDC features to enable efficient memory use. Both fixed-length and variable-length segmented capture aim to greatly reduce the amount of data collected, by effectively removing long stretches of uninteresting "off" times in the pulses. Whereas fixed-length segmented capture orchestrates fixed-sized data segments, VLSC dynamically stretches the segment length to include the whole burst of power above a specified power threshold. An analyst may choose to specify the number of segments acquired or total acquisition time of all the segments.

DDC, on the other hand, reduces the data by only looking at the spectrum of interest, as opposed to the vast frequency range enabled by a 256 GSa/s sample rate. We start by sampling the analog signal with a full sample rate of 256 GSa/s. Using a DSP process strictly in the digital domain, the incoming high-frequency signal is mixed with a locally generated sine wave, shifting the spectrum from its original position to baseband. Unwanted higher frequency components may now be filtered out using a low-pass filter, ensuring that the signal of interest is isolated. The magic happens at the next step, when the signal is decimated to a lower sampling rate, thereby saving computational resources and memory. Without DDC, a much larger data set would need to be processed in VSA. In the end the DDC from the scope and VLSC enabled by the VSA are a powerful combination for reducing the data to only what's important.

With the VSA software, the analysts can quickly and efficiently analyze the large data sets of pulse signals that span potentially many gigahertz in frequency. Using the 89601BHQC PathWave VSA Radar Pulse Analysis, they can automatically identify, label, and catalog pulses in tables describing various figures of merit, like power droop metrics or modulation types. Analysts can then extract parameters such as time, amplitude, frequency, phase, and modulation information and visualize them using tools like trace types, statistics, and modulation measurements in the frequency and time domains. Figure 2 shows three ways to visualize frequency hopping pulses using the VSA: frequency versus time plot, a spectrogram, and a table.

The advanced pulse train search feature of the VSA enables analysts identify emitter signature patterns using metrics such as pulse repetition interval, pulse width, hopping frequency, and more. An example of pulse train scoring in action is shown in Figure 3, where pulse patterns are depicted in a power versus time plot and a pulse metrics table. The VSA software enables emitter classification by automatically detecting pulse sequences as identified by metrics of interest. The table may be sorted by output power, frequency, and modulation type. Using the configuration table, analysts can define the different emitters from their pulse characteristics and organize and group them by color.