Interfering with radar signals is very important for electronic war and threat simulation systems

Dojammer 2021-05-11

Activating technologies enable meaningful characterization of radar, electronic warfare, and threat emulation systems

Modern radar / electronic war signals (EW) are more diverse than previous signals. Frequency agility, low likelihood of interception (LPI), larger bandwidth, and staggered pulse repetition intervals (PRIs) pose measurement challenges as pulses now need to be captured over a longer period of time to see a radar mode or electronic attack system (EA) under test to ensure that they work properly. With signals from technology lasting 30 seconds or more combined with greater bandwidth, the challenge of effectively capturing, analyzing, and reporting results is even more critical.

EA, RGPO fault example

A basic technique for jamming signals signal jammer against a radar to prevent it from successfully tracking a target is called Range Gate Pull Off (RGPO). Imagine a situation where an electronic attack system (EA) aboard an aircraft needs to block surface-to-air missile radar to prevent the missile from launching or being guided towards the aircraft. In this example, the distance from the rocket launch point to the aircraft is 10 km. It is believed that it will take about 20 seconds for the missile to reach this distance - an important timeframe for the acquisition of pulses.

Bluetooth Jammer

With the RGPO, the aircraft EA system listens to the missile radar and then takes advantage of the range gates in the radar tracking system by generating false radar return signals. The interfering signals received at the radar receiver are larger than the real radar RF impulse reflections, possibly 10 dB to 20 dB larger, and slowly move away from the location of the real reflections (see Figure 4, page 26). This causes the range finders in the radar receiver to be subtracted from tracking the real reflections and made to track the spurious signals for false echoes. Then the jammer pulses disappear and the radar breaks its trail.

Requirements for the acquisition of RF pulses

To effectively evaluate Jammer RGPO operation, the goal is to capture each radar reflection pulse and jammer pulse over several 10-second RGPO cycles. Using a full scan at 128GSa / s with or without segmented acquisition is not sufficient to acquire pulses over an RGPO cycle. In addition, an upgrade time of 5 µs makes it difficult to use fixed segments due to a lack of pulses during the upgrade dead time.

Segmented acquisition with variable width

A better approach is to use segmented variable width acquisition and real-time digital downconversion, where an IF trigger detects when a signal is present and only stores samples in segments when it is present. This eliminates the dead time between pulses and maximizes memory usage. Now, in-phase and quadrature-phase (I and Q) data at 800 MSa / s for a bandwidth of 640 MHz can be used to capture the modulation on the carrier, expanding the scope's memory.

The overall scenario time, including the potential flight time of the missile, that RF pulses can be captured has increased significantly. The VSA software can capture 83,000 pulses in record mode with the BHQ radar pulse option, which is about 50 seconds of scenario time. This is more than enough to analyze the flight time of 20 second missiles as well as several 10 second cycles of the RGPO engagement including pre-launch interaction. Includes checking the RGPO process by showing PRI in Trace D.

Conclusion

Modern real-time oscilloscopes such as the Keysight UXR enable exceptional performance when directly sampling signals up to 110 GHz. The combination of this raw power with segmented acquisition and digital down-conversion enables better insights into signals of interest and long-term trends.