Discussions on signal interference were once mainly limited to electronic warfare forums. But with the rise of autonomous driving technology, interference has become a common topic. Now, it is useful to understand some basic concepts about the test configuration necessary to evaluate the resistance to scrambling techniques and the principles of signal propagation. Many complex advances in signal interference are due to the work of radar. Therefore, it is useful to review some basic principles of radar.
The concept of radar is of course that the target reflects part of the energy of the transmitted signal. Receive and process the returned energy to detect the target and extract its position and relative velocity. If the original antenna beam is narrow enough, the direction of arrival of the return signal can also show the angular position of the target. If there is relative motion between the target and the radar, the carrier frequency offset of the reflected wave (ie, the Doppler effect) is a measure of the target’s relative radial velocity and can be used to distinguish between moving targets and stationary objects.
Typical radar transmitters emit signals in pulses. And pulses usually have a low duty cycle, where the duty cycle is the ratio of the duration of the pulse within the pulse period. In addition, the resolution of radar (and lidar) is limited by the pulse width. For example, a 1 microsecond pulse extends more than 150 m in space. Therefore, a radar emitting a 1 microsecond pulse cannot distinguish a distance less than 150 m.
However, frequency modulation is a method used to increase the range resolution of radar signals to less than 1 / (pulse width). Peeping is a signal whose frequency increases or decreases over time. There are many types of whistle-linear, nonlinear, exponential, etc. Some systems also emit compressed pulses to reduce transmitter power and the possibility of interception. Overall, the subject quickly became complicated. Therefore, the FM radar includes a stage that modulates the transmitted pulse, transmits the pulse, receives the echo, and then correlates the received signal with the transmitted pulse.
After the radar has sent a second pulse, there may be ambiguity when the energy returns from a distant target. This second time is called echo. In order to clearly measure distant objects, the radar must wait for its pulse to return. However, the fastest target that the radar can clearly measure is determined by the frequency of the transmitted pulse, which is the repetition frequency of the pulse. In order to measure the speed of fast objects, the PRF must be very high, which will cause a compromise between radar distance and speed detection.
One thing to note is that radar gps jammer usually have range advantages over target radars. This is because the signals from the jammer to the radar all indicate that the path loss is 1 / R2, and the radar backhaul is 1 / R4 loss when it bounces back from the target.
With these points in mind, consider the different types of radar jamming methods defined in electronic warfare. The barrage jammer attempts to submerge the interference signal in the receiving frequency band in the radar receiver. The noise jammer uses phase or AM noise to modulate the jamming signal. Misleading jammers use repeaters or memory to generate copies of radar echoes and make appropriate changes in time or frequency. Repeated interference will modify and retransmit the received radar signal, so the generated echo will relay inaccurate locations. Similarly, a transponder jammer is a transponder that can replicate a stored copy of a signal after receiving a radar signal trigger.
A related mode is to establish interference, where the receiver measures the frequency of the threat radar and adjusts the oscillator to retransmit it. Scan the jammer as above, scan the oscillator in the frequency band used by the radar receiver. Finally, some electronic warfare terminology applies to military exercises. A long-range jammer is usually an aircraft. When it blocks the aircraft’s radar and attacks the aircraft, it will stay away from the hostile weapon, while the repeated jammer performs the same operation when it is close enough to shoot in a hostile manner
Anti-jamming techniques generally attempt to counteract these efforts by taking measures that include changing the radar pulse synchronization mode. However, the synchronization properties can also change according to the radar mode (search, acquisition, monitoring). In addition, adjusting the timing of the pulse allows the radar to clearly assess the range and speed of the target. In terms of radar development and anti-jamming, the focus is on simulating radar configuration or anti-jamming with test instruments before committing to hardware or software design.
A common method is to synthesize complex pulse modulation and pulsation waveforms on tools such as Matlab, and then pass the information to an arbitrary waveform generator to create a waveform. There are also dedicated software packages for creating waveforms, such as Signal Studio by Keysight Technologies.
In test setups, waveform generators are often used to add real effects to the signal flow, such as jitter and wobble, changes in pulse repetition rate, and center frequency. The pulse creation software can also add effects from antenna patterns and specific radiation quality.
In addition, modern test instruments often contain multiple functions that help create radar signals based on benchtop instruments. For example, you can find high-end signal analyzers that integrate swept spectrum analysis, FFT analysis, RF and baseband vector signal analyzers, and noise factor analyzers.