Test & measurement
A finger on the pulse!
Phase coherent multichannel pulse analysis on radar systems
The R&S RTO and R&S RTP oscilloscopes combine phase coherent multichannel RF signal analysis with extensive functions for signal integrity and digital interface testing. This makes them an excellent choice for radar module analysis, as Ezer Bennour and Dr. Andreas Ritter explain...
jammers on defence platforms. Modern jammers not only attempt to disturb and overload enemy radar systems but they also create false targets. The jammer core is a DRFM, which stores a digital image of the enemy radar signal and retransmits it using modified parameter values. For DRFM characterisation, the receiver input signal and the transmitter
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output signal of the DRFM module are analysed simultaneously. An important parameter is the time delay between the incoming radar signal and when a copy of this signal is available at the transmitter output. Oscilloscopes can directly acquire even higher frequency radar signals. For
example, the R&S RTP with 16 GHz bandwidth covers nearly the entire Ku band and fully covers the X band, which is important for defense applications. As a result, the R&S RTP can be directly connected to the DRFM frontend, with no need for signal downconversion.
scilloscopes have multiple measurement channels and can correlate their signals. This makes them suitable for multichannel analysis on digital radio frequency memories (DRFM) deployed in
Even the standard functions of the R&S RTP provide extensive analyses
in the time and frequency domain. Fig. 1 illustrates the simultaneous acquisition of the input and output signal of a simulated DRFM including frequency hopping analysis. The spectrogram shows that while the original and the replicated signal in the DRFM match well, there are slight distortions in the manipulated chirp. The 6 µs time difference (clearly visible in the left part of the screenshot) is intentional, since a range gate pull-off scenario is being simulated, with the jammer retransmitting the replicated signal with a delay to create a false range target. In cases where the pulse repetition interval (PRI) is only slightly extended
after each pulse, it is worthwhile to check whether all transmitted pulses comply with the required parameters. The R&S RTP has an acquisition mode suitable for this purpose. In normal mode, the instrument cannot detect any pulses while the acquired data is being analysed by the processor. By contrast, in fast segmentation (or segmented capture) mode, the oscilloscope memory is first filled with the acquired data, then analysis starts. This reduces oscilloscope blind time to below 350 ns compared to normal acquisition mode. Once all the acquired data is saved to the oscilloscope memory, the
time domain trace of the data can be displayed. Fig. 2 shows the envelopes of the original and the replicated pulse, which are calculated using math functions, and the time delay between the two pulses, which is determined using the delay measurement function.
Fig. 1: Simulated DRFM scenario. The replicated pulse (DRFM pulse, orange) is delayed by 6 µs relative to the original pulse (yellow), and its amplitude is nearly twice as high. The spectrogram shows that the frequency and chirp match well, while the replicated (DRFM) signal exhibits distortions (white arrows).
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AnAlySiS OF A RADAR wARning REcEivER The oscilloscope trigger unit allows triggering on a signal different from the signal to be examined. For example, a serial bus used to control a T/R module can be decoded and used as a trigger source. Another useful trigger application is to isolate a specific radar signal in a scenario with multiple radar transmitters. Figs. 3 and 4 show a scenario of this type generated with the R&S Pulse Sequencer software. An airborne radar is tracking a target and moving laterally past the target. Additional radar signals come from an imaginary patrol boat and a stationary air surveillance radar. This signal mix is output by a dual-channel R&S SMW200A signal generator, simulating the outputs of two receive channels of a multichannel radar warning receiver (RWR). The objective in this example is to isolate and analyse the airborne radar signal. The oscilloscope trigger unit allows the pulse characteristics of the signals to
August 2021 Instrumentation Monthly
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