SPO-15 Beryoza For the MiG-29A Fulcrum
The SPO-15LM for the DCS: MiG-29A Fulcrum module is built using a new physics-based approach. The system simulates a more realistic signal environment in order to ensure the most realistic behavior, algorithms, and limitations of the modelled SPO-15LM RWR system.
The new system comes with a radar database containing signatures and behaviors for each radar system in the game, including details like carrier frequency, waveform type and (if applicable) pulse train pattern for different operational modes, antenna and transmitter properties, search strategy depending on range and altitude of the target, signal variability, and CCM used etc. All of this information is used in two ways: to calculate accurate power density at the receiving antenna at each time step, taking into account the physical properties of the signal and the directivity pattern of the transmitter antenna, and to permit realistic modelling of the RWR system itself.
On the receiving end, the antenna and receiver properties are similarly taken into account in order to obtain a physically accurate estimate of received power. Each antenna and receiver channel is processed independently. This is critical for accurate modelling of the Soviet systems as they do not use amplitude comparison to estimate emitter azimuth; instead, each of the azimuth channels on the display corresponds to its own set of an antenna, a receiver, and initial processing hardware. As a result the coverage isn’t always 360 degrees. The antenna beamwidth varies with frequency and the antenna gain varies with azimuth and elevation, which causes the detection range and signal power for each emitter to vary not just with radar type and work mode (with the radar transmitter power and antenna gain being the deciding factor rather than its target detection performance) but also with orientation of the aircraft. The emitting antenna directivity pattern is also simulated, which means that, at low distance and high transmitting power, side lobes will be picked up and head-on emissions will bleed into receiving antenna side and back lobes blinding the device. Conversely at low signal power, the system develops blind zones all around the aircraft, and the RWR might fail to pick up the main lobe unless it passes directly over it. The unusual antenna coverage of SPO-15LM in particular requires the pilot to be aware of these blind zones during combat.
The improved simulation of signal propagation, together with attached signal signature (PRF, pulse width etc.) allow for accurate modelling of the signal processing algorithms used by the system. The SPO-15LM, while being an analog system, performs many tasks that are normally relegated to digital systems, and some of these analog systems use vastly different approaches compared even to early western systems, which leads to numerous quirks and limitations that are now accurately replicated. The most obvious, as already described, is how the threat azimuth is determined: The airspace around the aircraft is divided into eight azimuth channels covered by 10 azimuth antennas (with, notably, the two forward-facing antennas furthest off-nose on each side merged into a single processing channel), and two elevation channels covered by two elevation antennas. Each of these channels is processed separately with a fixed signal power threshold to activate each channel. The only time the signals are combined is to measure the signal power for the power level display (which now shows the actual signal power in 2 dB increments from threshold, rather than a simple function of range) and for the target priority algorithm. Lack of combined processing also means that coverage of each channel will vary with emitter power and frequency. The system features compensation systems, but they are crude and their effectiveness varies with signal power. The identification and target priority circuits also process each channel separately, meaning that in rare cases the same threat might even be interpreted differently in two neighboring channels, and two threats on opposite azimuths might both be interpreted as a single, main threat if the signals sync up.
The identification process involves measuring the repetition time and pulse width of the signal and sorting it into very broad PRF/PW bins. The measurement of PRT can fail if it’s not stable (e.g. due to jitter) making some radars impossible to identify. The presence of multiple emitters in the same sector will also interfere with this process. Even if this part succeeds, the low number of signal parameter bins means that the system might still assign the wrong type to the threat if the signal parameters are close enough. The system is also able to separate Continuous Wave (CW) signals from pulsed signals, and to interpret colocated CW and pulsed emitters as a single emitter in Semi-Active Radar Homing (SARH) guidance mode; it cannot however distinguish between different CW radar types, meaning this feature is susceptible to false alarm. Pilots thus need to be weary of the fact that the system will not always be able to accurately identify the threat type. To improve usability of the system, the threat program is generated automatically based on known threats present in the mission and is provided in the kneeboard for every flight - in reality, the threat program cartridge was issued to units based on the threats present in the combat theatre, and was not designed to be field reprogrammable. The friendly emitters are not included in the program, but they might still be falsely identified as hostile for reasons described above. The system also has an ability to sort the signals into 2 bins by carrier frequency, however in the MiG-29 this feature is permanently disabled, as it requires each sub-band to be scanned separately, reducing probability of detection against radars in search mode (the MiG-29 lacks the full control panel which would allow this function to be switched on and off).
The target priority circuit is similarly modelled with its limitations. For instance, the system takes flight altitude into account for the priority algorithm, but it has to be entered manually. In the MiG-29 in particular it is forced to a high setting (8-16 km) without any way to adjust it, meaning, Short Range Air Defense (SHORAD) systems are always treated as low priority. The system will also prioritize radars in track mode over search mode. But again, track mode is recognized entirely by the length of the illumination event being above a certain threshold, so at high signal power emitter side lobes might falsely trigger the track warning. For the priority threat, the system displays the signal power (as well as the highest estimate of weapon range for the given type in terms of equivalent signal power) and the elevation - the latter only being available at high signal power due to much lower sensitivity of the elevation channels.
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Phant
