By: Rohde & Schwarz India Team
Today, system and RF engineers face ever-increasing challenges and complexities when testing state-of-the-art multiport EW receivers. Generating real-life test signals in the lab is still the top goal when evaluating EW receivers.
Optimizing EW simulation realism in lab testing ensures that an EW receiver is ready for flight testing which can cost millions of dollars per hour and must be scheduled months in advance. Lab testing, therefore, reduces cost and schedule risk by ensuring that the EW receiver passes flight testing the first time.
Lab testing must be done with a progression in test complexity in order to determine whether test failures come from the receiver under test or the test stimulus. As test complexity increases, so does the test realism but so do the difficulties in troubleshooting failures and verifying scenarios. For example, the simplest type of test simulates only one mode of one emitter at a time and sequences through all modes of all emitters stored in the look-up table on the EW receiver. Any failures at this stage are easily traced to either the test stimulus or the EW receiver. Longer, more complicated scenarios can then be created using combinations of the same emitters for multi-emitter testing with power scaling for range, motion, and antenna scan effects and angle-of-arrival (AoA).
Radar warning receiver Function and Signal Generation for EW Test
Radar warning receiver (RWR) RWRs are designed with numerous trade-offs affecting the ability to intercept, sort, and identify the pulses of enemy radars called “threats”. For example, sensitivity can be traded-off for instantaneous bandwidth to give the greater probability of intercept of closer threats at diverse frequencies at the expense of intercepting threats further away. Different angle-of-arrival methods trade-off accuracy for bandwidth and speed.
Since the effects of the trade-offs are measured in testing, the signal generators used to simulate threats at RF must have better simulation fidelity than the specifications of the receiver. Simulation fidelity can be described in at least three different ways.
The first is the basic RF performance of the simulation at RF which depends on the RF performance of the signal generators used to simulate threats. The signal generator should generally have better performance than the RWR being tested. Specifically, the signal generator should have a better spurious-free dynamic range, image, and LO feedthrough performance than the spurious performance of the RWR because the RWR will attempt to classify all spurious signals.
The signal generator must also be able to produce lower power levels than the sensitivity of the RWR to ensure that the RWR can detect threats and their scans at the expected range. Simulating other threat parameters such as modulation-on-pulse, frequency diversity, and antenna scans require the generator to have at least one baseband generator with adequate bandwidth and resolution (effective bits).
The second way RWR performance is measured is in its ability to sort and track multiple threats at the same time, or at least one threat in the presence of other pulses. This requires more signal generation resources and the ability to qualify the simulations which are often built from single-emitter scenarios. Some signal generators, such as the SMW200A vector signal generator, can have multiple baseband entities to add pulse density and threat density at RF without increasing the number of signal generators in the scenario.
Finally, it is important to simulate the physical location of emitters since RWRs use angle-of-arrival (AoA) measurements as a primary sorting parameter and this must be simulated at RF as well. This brings us to the third way simulation fidelity, i.e- AoA simulation performance, which is the accuracy of AoA simulation using amplitude, phase, and time offsets between synchronized generators after a calibration. Simply put, the signal generators should have better AoA simulation performance than the SUT. How much better depends on the required uncertainty in the simulation.
Mission Data File Testing
The simplest form of testing is called “mission data file testing.” Mission data files are software look-up tables that contain information about the emitters the receiver must identify by their waveform parameters and antenna pattern and scan. The parameters include frequency, pulse width, pulse repetition interval, modulation on the pulse. Testing the receiver’s mission data file requires emulating each mode and beam of the emitters in the file at RF with power scaling due to range, antenna pattern, and scan. This type of testing verifies whether an EW receiver can identify all modes and beams of an emitter and whether the emitter can be tracked through these changes. The key to this form of testing is to reproduce the parameters in the mission data file accurately. The emitters must be simulated at RF with high spurious-free dynamic range (SFDR), low harmonics, and high-frequency accuracy and stability. Timing parameters such as pulse width and pulse repetition interval must be accurate and stable. Modulation-on-pulse is often required, and this requires a signal generator with adequate bandwidth and spectral purity to reproduce the modulation. Closely related to SFDR requirements is amplitude resolution to simulate the antenna beam pattern with sidelobes and the antenna scan. Simulating an antenna scan using an IQ waveform segment for each pulse with a power offset can consume a large amount of memory, so a signal generator that plays pulse descriptor words (PDWs) greatly streamlines emitter mode and beam creation in MDF testing. This is because PDWs are digitally parameterized descriptions of output RF pulses that are described in tens of bytes while arbitrary waveforms are full signals at baseband which consume tens of kilobytes or megabytes, one for each pulse in an antenna scan. The Pulse Sequencer software enables both manual and automated threat creation and sequencing. Libraries of pulses, sequences, antenna scans, and patterns can be combined into different threats and sequenced using “Emitters (Collection)” or “Localized Emitters” scenarios.
Multi-emitter simulation is performed to determine if an RWR can track one or more emitters with increasing levels of pulse density to emulate a real threat environment and electronic order of battle (EOB). D. Adamy defines EOB as “the number and types of electronic systems arrayed against you” and it changes with time. For example, a strike aircraft approaching a coastline will first be illuminated by acquisition radars in L-S band. As it nears its objective, it may be illuminated by both the acquisition radar but also by one or more tracking and fire control radars at X-band. The latter will use much higher pulse repetition frequencies (PRFs) resulting in greater pulse density. Often, the pulses from different emitters will overlap in time, which is called “pulse coincidence” or “time coincidence” or “pulse-on-pulse.”
This is especially true when emulating tracking and fire control radars which alternate between medium and high PRFs to resolve range and Doppler ambiguities from medium and short-range targets. Multi-emitter simulation can be done with “Emitters (Collection),” or “Localized Emitters” scenarios. “Emitter Collections” replays emitters collected and stored in a list. “Localized Emitters” allow the users to place emitters on a 3D map, define emitter trajectories and preview the configured scenario with powerful animation features which makes them better for simulating EOB.
If you can stay ahead of technological advancements in radar and EW then you need to understand how to create and validate EW scenarios of single emitters for mission data file testing and multiple emitters with pulse-on-pulse. For example, You can create the scenario using the Rohde & Schwarz Pulse Sequencer software and the SMW200A vector signal generator. The scenario can be validated using the Rohde & Schwarz FSW signal and spectrum analyzer and K6 Pulse Measurement application.
Rohde & Schwarz is going to organize a webinar focusing on Efficient testing of multiport EW receivers”. Starting with the requirements of testing basic pulse processing in Radar Warning Receivers (RWR), this webinar discusses and demonstrates the generation of phase-coherent multi-emitter signals without pulse dropping (pulse-on-pulse). Specifically, it proves the applicability of a scalable COTS RF radar signal simulator for comprehensive testing of multiport RWRs.
In this webinar, you will learn how to/ more about:
- solutions for complex radar scenarios and signal generation
- generation of phase-coherent multi-emitter signals
- how to address test challenges of multiport Radar Warner Receiver (RWR)