Early warning aircraft used to be the most focused special aircraft, but with the entry of the PLA into the era of KJ-500, it was found that the anxiety about early warning aircraft has basically disappeared for both the Air Force and the Navy. A large number of KJ-500 and its improved versions have joined the military, helping the naval and air forces see through the fog of war. So, is KJ-500 the most satisfactory early warning aircraft in the eyes of the PLA? The answer is still negative.
Admittedly, with the addition of the air-to-air refueling pipe, the comprehensive performance of the KJ-500A has reached the world’s top level. However, the Yun-9 platform it uses still lacks a bit in terms of flight speed, the internal space is not large, and the size of the carried radar antenna is still relatively small. In future aerial combat, the electronic warfare capabilities of formidable foes and the proliferation of stealth aircraft will greatly compress the detection range of early warning radar. Therefore, continuing to increase the size of the radar antenna and expanding the detection range has become a new development direction.
This reminds us of the KJ-2000, the large early warning aircraft that was the first to serve in the PLA. The appearance of this model in recent years has been low because of its small quantity. Although it is an old model, the IL-76 platform is still more potent than the Yun-9 platform, with a larger antenna size, more space for electronic equipment, and stronger power supply. Therefore, after the service of the Yun-20B, developing a new large early warning aircraft based on it to replace the KJ-2000 and complement the KJ-500 has become a necessary choice. This early warning aircraft developed on the Yun-20B platform is tentatively referred to as “KJ-3000.”
Recently, Western commercial satellites captured a photo claiming to be a ground test platform for a phased array radar in China. Three differently sized and shaped disk-shaped radar antennas can be clearly seen. Based on the antenna design characteristics and size comparison, it can be inferred that the leftmost one is the fixed three-sided active phased array radar of the KJ-500, and the rightmost one is the mechanical rotating two-sided passive phased array radar specifically for Pakistan’s ZDK-03 early warning.
The radar antenna in the middle is quite unfamiliar. It seems to be a two-sided array similar to the ZDK-03, but the size is much larger. Obviously, it is not the fixed three-sided active phased array radar of the KJ-2000. So, its identity is likely the radar of the previously mentioned KJ-3000. From the picture, the KJ-3000 early warning aircraft has returned to the traditional circular antenna cover diameter layout, not using the three-sided array antenna of the KJ-2000 or a more advanced conformal antenna design.
The reason for arranging the radar antenna in the KJ-3000 like this is to maximize the antenna aperture, thereby improving radar detection range and performance to counter the electronic warfare capabilities of formidable enemies and the widespread use of stealth aircraft after 2030.
According to the radar detection range formula, the antenna aperture and radiated power determine two key parameters of radar detection performance. To improve radar detection range and performance, breakthroughs must be made in these two parameters. The existing KJ-2000 and KJ-500 of the PLA both use fixed three-sided array radars. The advantage of this design is that it can achieve electronic scanning in all directions simultaneously, allowing the radar to quickly intercept, confirm, track, and lock onto targets, adapting to saturation attacks and high-mobility targets.
However, the three-sided array antenna design inevitably requires concessions in aperture size, which to some extent limits the radar’s detection range and performance.
Now the U.S. Air Force is accelerating the development of the sixth-generation stealth fighter, and the first prototype may fly before 2025-2030, forming initial operational capability by early 2030. This also means that after 2030, the U.S. military’s sixth-generation stealth fighters, new generation stealth strategic bombers, and unmanned stealth combat aircraft will be deployed on the battlefield. The stealth performance of these aircraft is significantly improved compared to existing aircraft, posing a greater challenge to the detection capabilities of early warning aircraft.
To ensure that early warning aircraft have sufficient detection performance, increasing the antenna aperture is a very safe approach. Considering this, the KJ-3000 has abandoned the mature three-sided array antenna layout of the KJ-2000 and KJ-500 and returned to the traditional design of placing two arrays according to diameter. This is to better counter foreign sixth-generation stealth fighters.
Some may wonder why the KJ-3000 does not use a conformal antenna, which uses the fuselage skin as an antenna, to get a much larger antenna. In fact, domestically produced unmanned early warning aircraft have already adopted conformal antennas. The advantage of conformal antennas is that they integrate with the aircraft’s surface, with a very large antenna aperture and minimal impact on the aerodynamic performance of the aircraft.
However, conformal antennas are more difficult to design, and their cost and price are very high. In addition, conformal antennas have poorer forward and backward visibility detection performance, weakening the continuous situational awareness capability in the battle zone. Considering these factors, the PLA Air Force has decided that the KJ-3000 will continue to use a traditional antenna layout, leaving conformal antennas for use on long-endurance unmanned early warning aircraft.
Based on domestic and international experience, the diameter of the rectifier hood of an early warning aircraft radar antenna is at most one-third of the length of the aircraft and the thickness is one-third of the diameter. The length of the Yun-20 is approximately 53 meters, so the diameter of the KJ-3000 radar antenna hood is at most 17 meters, with a thickness of about 5 meters. This large antenna hood can accommodate antennas with a sufficiently large aperture to ensure the detection performance of the antenna.
Of course, this can only accommodate one or two antenna arrays. The disadvantage of a planar phased array antenna is that the scanning range is relatively small. As the scanning angle increases, the beam will widen, reducing the effective aperture projection area, and the radar detection performance will decrease. Therefore, a planar phased array antenna can scan an angle of approximately 120 degrees, and it cannot achieve omnidirectional coverage. Even with an additional array on the back, it is only 240 degrees. To achieve full coverage, a mechanical scanning mechanism must be added, but it is challenging to rotate such a large antenna hood, and the volume and weight of the mechanical rotation mechanism will be very large, placing higher demands on the carrier aircraft.
The Yun-20 large transport aircraft, however, uses advanced aerodynamic layout, active control technology, and fly-by-wire systems, providing excellent flight stability and performance. It can provide a good working environment for both crew and radar. Additionally, the latest Yun-20B uses domestically produced WS-20 high bypass ratio turbofan engines, which have low fuel consumption and low noise, further improving the aircraft’s working environment.
The internal space of the Yun-20 large transport aircraft is also very large, allowing for the installation of more display consoles and communication equipment. In air combat between fighter jets, early warning aircraft need to provide detailed command guidance, requiring the aircraft to have a large internal space to install more equipment. Judging from the internal space of the Yun-20 large transport aircraft, it can accommodate more than 10 display consoles, providing command guidance for more than 20 fighter jets.
The KJ-2000 early warning aircraft was equipped with the military in 2007, and it has been in service for nearly 20 years. Due to the fact that it uses second-hand IL-76 large transport aircraft, which are even older, the KJ-2000 will need to be phased out after 2030 and replaced by the KJ-3000. This means that the PLA Air Force will form a combination of the KJ-3000 and upgraded KJ-500 high and low early warning aircraft after 2030 to deal with a more complex battlefield environment.