Electronic Military & Defense magazine was developed for engineers, program managers, project managers, and those involved in the design and development of electronic and electro-optic systems for military, defense, and aerospace applications.
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Techniques Effective Capture, Measurement, Analysis, And Emulation Of Radar Jamming Signals Commercial-off-the-shelf (COTS) approaches can provide the foundation needed to keep pace with evolving threats in radar and EW applications. by John Hansen D eceptive jamming typically works as a time-series of events coordinated to confuse radar tracking algorithms: range tracking, angle tracking, Doppler tracking, or all three. In the lab, effective emulation of jamming techniques starts with the capture, measurement, and analysis of real-world signals. A pair of commercial-off-the-shelf (COTS) approaches can provide the foundation for characterization and emulation. One combines a signal analyzer with vector signal analysis software to support the capture, measurement, and analysis of jammer signals. The other uses signal-creation software, an arbitrary waveform generator (AWG), and a vector signal generator for the emulation of radar or jammer signals. These hardware and software elements support precise control of time- and frequency-domain parameters — a high degree of control in both domains helps ensure accurate results during characterization and emulation. Sketching The Overall Problem: Jamming Signals In a deceptive jamming scenario, the time-series of events typically includes four steps: search, identify, track, and jam. As an example, consider a range gate pull-off jammer. After a victim radar has begun to track a target with jamming capability, the jammer records the radar signal into a high speed memory. It then adds a slight delay to the recorded signal and sends it back to the victim radar along with the actual skin return of the target. Next, the jammer increases the power of the delayed signal to ensure that the radar receiver must reduce its gain (i.e., desensitize itself) to avoid overload. At this 30 Electronic Military & Defense ■ www.vertmarkets.com/electronics point, the victim radar can no longer see a skin return from the target aircraft. During each successive pulse (or group of pulses) the jammer adds small amounts of delay to the victim radar signal. This causes the victim radar's range gate to follow the spoof signals. As a final step, the jammer switches off, leaving nothing but noise for the victim radar to track. The radar will then break lock, and the target acquisition process must restart. Understanding The Typical Measurement Problem Such "range deception" jamming signals use a dynamic pulse repetition interval (PRI). This presents several challenges to swept spectrum analyzers, which have been the traditional way to measure and analyze jammer signals. Unfortunately, typical swept analyzers are not equipped to provide accurate, repeatable measurements of current-generation signals that have a dynamic PRI. The problem: As the instrument sweeps across the spectrum, signal information is missed if it occurs away from the local oscillator (LO) frequency (i.e., the center of the sweep) or during the reset interval between sweeps (see Figure 1 on the previous page). In general, this prevents measurements of Doppler or phase information from pulsed signals. Figure 1: During each sweep, information is lost when signal activity is away from the LO frequency and during each sweep reset. Swept techniques such as the line spectrum and zero span work when PRI is stable; however, neither technique can be used to accurately characterize signals that have a dynamic PRI. For example, a line-spectrum measurement uses a narrow resolution bandwidth of approximately 0.3 times the PRF.