TREE FORK / Suuji BMEWS Radars
China operated the TREE FORK / Suuji missile early warning radars in the 1970s. Consistent with threat perceptions in that period, they were oriented towards the Soviet Union, and would not have provided warning against attacks from the United States. These radars are largely un-attested in the open source literature. There is a single mention of the Suuji radar in a declassified DIA document from 1972 that has been online for many years. It was not until June 2014, that Tim Brown found a declassified NPIC imagery interpretation report that the existence of TREE FORK came to light.
Although a gradual Soviet military buildup in the Far East had been ongoing since the early 1960's, it apparently was not viewed in Peking as a serious threat or a significant alteration of the forces balance. But in 1969 border skirmishes escalated, and the threat of a major war with the Soviet Union loomed large. Almost immediately thereafter, a reorientation of the PLA commenced greatly strengthening the northern border. These moves shifted the focus of the PLA's defenses from seaward approaches to the concept of all-around defense. Subsequently the threat of war between China and the USSR diminished, along with Soviets hints of preemptive nuclear strikes. But improvement in China's military preparations continued.
By the latter part of 1969, the Chinese had recognized the Soviet threat as the most ominous and immediate as any confronting them. Since that time, China augmented its ground and air force elements deployed in the military regions and air districts contiguous to the border. This augmentation has been modest and the bulk of the forces remained in a defensive posture considerably removed from the border.
Since the advent, of the nuclear-tipped ballistic missile, the Soviets have dedicated significant numbers of nuclear, land-based missiles to theater warfare missions. No theater was neglected, though the European theater always commanded the greatest attention. In the late 1960s, the Soviets began to draw down obsolescent missiles, replacing them with ICBMs and adding coverage of the new enemy - China. Medium-range missile launchers are capable of firing nuclear, conventional, or chemical munitions, and consisted of the FROG (and its SS-21 replacement), the SCUD B (and its SS-23 replacement), and the SS-12/SCALEBOARD (and its SS-22 replacement). By the mid-1980s the Soviet Union deployed about one-quarter to one-third of its military forces in its Far Eastern theater. In 1987 Soviet nuclear forces included approximately 171 SS-20 intermediate-range ballistic missiles, which China found particularly threatening.
In the 1970s and 1980s the USA and USSR acquired credible options to launch on warning (firing strategic nuclear forces almost immediately upon receiving reports of enemy missile launches from ground- and space-based warning sensors), and so the utility of a nuclear first strike declined greatly. Absent such capabilities, China would be forced to absorb the brunt of a Soviet preemptive or preventive strike before it could retaliate. While China might not require the exquisite warning capabilities of the superpowers, just as radars were deployed to develop situation awareness of the air threat, so to might radars be deployed to provide warning "With Chinese Characteristics" of Soviet missile attacks.
The TREE FORK 2, a large Yagi antenna, was first seen in January 1971 at the Suuji Air Warning [AW] Radar Facility, which was eventually abandoned. The TREE FORK 2 consisted of 32 Yagi elements, eight across the horizontal boom and stacked four high. By 1971 a facility for producing this new Chinese long range early warning radar, also designated SUUJI, had been identified by DIA at Sha Sheik. The new radar, which was first seen in 1971, greatly increased China's early warning detection capability. It was believed that up to ten of these radars had been deployed by 1971.
The Suuji D large Yagi radar was first seen at Lashanyouqi AW Radar Facility in January 1973. The Suuji D had 40 Yagi antenna elements - ten across the horizontal boom and stacked four high. By 1979 there were eight [or nine, depending on counting rules] sites at which the Suuji D, Suuji E, and TREE FORK radars were deployed. The much larger Suuji E had 40 Yagi antenna elements - twelve across the horizontal boom and stacked eight high. These sites were in the northern half of China and were capable of providing radar coverage of most Soviet land-based missiles launches in the theater as well as SLBM launches from the northern Sea of Japan.
The early history and provenance of these radars is unknown.The TREE FORK 2 designation implies a TREE FORK 1, just as the Suuji D and Suuji E designations imply the existence of Suuji A, Suuji B, Suuji C, and Suuji D. But these are not attested. Nor is the logic of the shift from the TREE FORK nomenclature to the Suuji designation apparent.
One possible predecessor is the SA-2 (V-750) Soviet medium to high altitude surface-to-air missile system uses the P-12 (NATO designation Spoon Rest-A truck-mounted or Spoon Rest-B) early warning radar and usually six reload rounds on their articulated trailers. The battalion's early warning and target acquisition Spoon Rest A-band radar has a range of 275 km using a large Yagi antenna array. The original Spoon Rest radar had 12 Yagi antenna elements - six across the horizontal boom and stacked two high. The later Spoon Rest D, a more powerful variant of the Spoon Rest radar system, radar has 16 Yagi antenna elements - eight across the horizontal boom and stacked two high.
The Chinese copy of the Soviet Knife Rest HF yagi radar, designated Bean Sticks, operates in the 70- to 73-megahertz frequencies with a range of about 180 kilometers. These radar have 4 Yagi antenna elements - two across the horizontal boom and stacked two high.
One Yagi radar in widespread Chinese use today is the CETC JY-27 Wide Mat VHF Band Long Range 2D Surveillance Radar (low band "anti-stealth" early warning), which could be placed with the other "JY-" emitters. The JY-27 Wide Mat radar has 96 Yagi antenna elements - sixteen across the horizontal boom and stacked six high. Chinese proliferation to Syria is limited to advanced air defense radar systems providing significant increases in capability over extant Soviet-era systems in service. Little mention of Chinese radar sales to Syria is found in open sources. Chinese JY-27 (Wide Mat) 2D radars are located at two EW complexes in central Syria.
Around the year 1960s the US sought to modify an existing Semi-Automatic Ground Environment (SAGE) Air-defense radar to fulfill the SLBM warning role. The AN/FPS-26 was normally used as a height-finder in conjunction with the SAGE/Back-Up Interceptor Control System (BUIC). Major changes included a “slight” increase in transmitted power to achieve greater range (at least several hundred miles beyond the 220 n mi figure, a decrease in the radar’s pulse repetition frequency to compensate for the longer individual pulse travel time to and from the target, and a reshaping of the radar’s antenna to reflect the changed gain and pattern requirements.
Log-periodic or Yagi-type antennas commonly are used to generate VHF/UHF radar signals. Antennas can be classified in several ways. One way is the frequency band of operation. Others include physical structure and electrical / electromagnetic design. Most simple, non-directional antennas are basic dipoles or monopoles. More complex, directional antennas consist of arrays of elements, such as dipoles, or use one active and several passive elements, as in the Yagi antenna.
A Yagi-Uda array formed from a series of dipoles located in parallel in a common plane and forming a “wave channel.” One of the dipoles is the actively driven element and the rest are passive. One of the passive elements located behind the actively fed antenna plays the role of reflector, while the others, placed in front of the actively fed antenna, play the role of directors. The highest gain can be achieved along the axis and on the side with the directors. The reflector element reflects power forwards and thus acts like a small ground plane.
The Yagi antenna is inexpensive and effective. Their wide use is conditioned by high gain, good directional property, compactness, simplicity, and small weight. The aerial is used in the bands starting from short wave, in metric and decimetric bands and at higher frequencies, and in microwave ranges. The Yagi's frequency coverage is limited. Some compensation for this can be provided by varying the number of elements, their diameter, and the spacing between them. Yagi-Uda antennas are known to be difficult to design and optimize due to their sensitivity at high gain, and the inclusion of numerous parasitic elements. Generally, the more elements a Yagi has, the higher the gain, and the narrower the beamwidth.
The Yagi-Uda antenna was invented in 1926 by Shintaro Uda of Tohoku University, Sendai, Japan, with the collaboration of Hidetsugu Yagi, also of Tohoku University. Yagi published the first English-language article on the antenna in 1928 and it came to be associated with his name. However, Yagi always acknowledged Uda's principal contribution to the design, and the proper name for the antenna is, as above, the Yagi-Uda antenna (or array).
The Yagi was first widely used during World War II for airborne radar sets, because of its simplicity and directionality. Further practical and theoretical studies were undertaken, but in the late 1950's there existed no rigorous solution of the Yagi problem. The experimental results were restricted to special cases, with no attempt made to find a connection between them. This antenna was most commonly used for TV reception in the mid-20th Century [for those old enough to remember seeing them on every roof top].
Yagi antennas use arrays of parasitic electric dipoles. When the array is excited, the currents at each radiator may be decomposed into a surface-wave component plus a correction component. The surface-wave currents are of particular importance in design. Yagi-Uda antennas include one or more director elements, which, by virtue of their being arranged at approximately a quarter-wavelength mutual spacing and being progressively slightly shorter than a half wavelength, direct signals of increasingly higher frequencies onto the active dipole. Thus, the complete antenna achieves a distinct response bandwidth determined by the length, diameter, and spacing of all the individual elements; but its overall gain is proportional to its length, rather than simply the number of elements.
The forward gain of a Yagi antenna is to a large extent a function of the boom length regardless of the number of elements, whereas the frequency range of available forward gain, gain bandwidth, is related to the number of elements for a given boom length. Most often, one reflector is used, so the number of elements are determined by the number of directors in addition to the fed element and the reflector.
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