Essay: Long range air surveillance systems

There are many long range air surveillance systems employed throughout the world for a variety of reasons on a variety of platforms all bringing different advantages to the scenario in which they are employed. As is true of all radar systems no one system is suitable for all purposes and key trade offs need to be established when a prospective purchaser decides on the system suitable to their needs. With a view to draw some similarity without being drawn into a commercial comparison or system comparison, this paper will review systems which are land based. Two mobile military units and one fixed joint military and commercial unit have been selected. This provides some similarity whilst also providing suitable separation for demonstration purposes. The systems selected for review are the ARSR-4 (AN/FPS-130) Air Surveillance Radar, a coherent 3D Radar employed as a joint government and military radar system manufactured by Northrop Grumman, the AN/TPS-59(V)3 Tactical Radar 3D Air Route Surveillance Radar employed as a mobile military radar system manufactured by Lockheed Martin and the TRD-1235, a fixed mobile long range surface and air surveillance radar, designed by P??emyslid Institute of Telecommunications, Russia.
After much research it has proved impossible to determine a true and accepted definition of the term ‘long range’ amongst manufacturers and users alike, in any domain (air, surface or ballistic). That is the manufacturer tends to call anything with a range of 100nm or approximately 200km long range, but this also appears to be intrinsically linked to the radar cross section of the target the manufacturer claims to be able to detect. For example the Giraffe, a ballistic air surveillance system, claims long range status at a detection range of 60km although newer models have been extended to 180km. For the purpose of this demonstration the radar systems selected are considered long range in accordance with the manufactures designation. An additional problem revolves around radar cross section and which values should be used to evaluate which radar system. This paper has assumed the values provided by global security and has tabulated the ones relevant to calculations within.
Radar Cross Sections
Object Radar Cross Section (m2)
Mig21 (1)
3
Airliner / Cabin Cruiser (1)
10
Tomahawk Missile (1)
0.5
Generation 5 Fighter (JSF or similar) (1)
0.005
Man (1)
1
Coastal Trading Vessel (2)
300-4000
Table 1: Assumed Radar Cross Sections
The selection criterion for the radar systems was largely based on the availability of the Pulse Repetition Frequency (PRF) data. Without PRF it is difficult to demonstrate many of the lower lever range equations. Although a PRF can be determined from the average and peak power provided pulse width was also given, it was found that most systems held this information a closely guarded secret. This coupled with the absence of other key data required to process the radar range equation or at least the data to derive the key element of the radar range equation it becomes difficult to demonstrate foundation knowledge.
Each of the selected radars will be reviewed in turn. Where possible, determined on information availability, each radar will be presented with the same formatting. Basic tabulated data from manufacturers will be provided in the text of the paper with an addition column added to define the calculated data. The calculations will be added as annexes to the paper with an annex specific to each radar system. A logical conclusion will be utilised for each radar system to define strengths and weaknesses as wells as any significant discrepancies identified between the tabulated and calculated data, prior to concluding with overall observations made during the review process.
ARSR-4 (AN/FPS-130) Air Surveillance Radar
Country of Origin: United States of America
Manufacturer: Northrop Grumman
Role: The ARSR-4 is designed to meet the joint air traffic control and air defence sensor requirements of both the Federal Aviation Administration and the United States Air Force (3). The ARSR-4 is capable of operating on Mode S and Mode 4. The ARSR-4 is specifically designed for target acquisition and tracking.
Design Radar: The ARSR-4 is a part of a joint multi-model (TDWR, ARSR-9, ASRS-11 and ARSR-4 (4)) network of radars which include up to 400 stations. The ASRS-4 is primarily stationed around the CONUS (4) which is defined as the coastal region of the USA. The ANSR-4 was noted to show an improved performance (this model of radar extended the range of its predecessor by 50nm) over the ARSR-3 during OT&E however suffered reliability issues at some sites (5). The ARSR-4 was designed to detect a 2.2m2 radar cross section target within this volume at any range less than 200 nm with a probability of 80 percent or greater (5).
The radar is designed as a coherent (multiple frequencies combining to make a pulse) 3D radar operating in the D band (1.2 -1.4 Ghz) (3). It is based on a solid state RF amplifier which allows the ARSR-4 to operate at low voltages, reliably (6). The use of a solid state RF amplifier results in the production of excess heat, this problem is resolved through fixed cooling apparatus, achievable as the ARSR-4 is a fixed site system. Additionally the use of a low voltage solid state RF amplifier enhances the user friendliness of repairs and maintenance, particularly on remote sites.
The radar uses an array fed ray dome covered aperture which produces side lobes of -35db (3162.27) or less as well as circular polarised radiation (3), allowing the radar to have enhanced detection of aircraft in poor weather conditions. This coupled with a low PRF allows the radar to detect targets at long range unambiguously in bad weather at the expense of information refresh rate. The primary reason the radar would be employed along the coastal region is its ability to detect targets in atmosphere that has high water content. As this is not a necessity in the central regions of the continent the other models/systems have been employed to capitalise on other trade-offs.
The radar system utilises Doppler pulses to reduce clutter to a reported range of 400km. Doppler pulse radar reduces clutter by filtering out all returns which aren’t detected to have a minimum speed set at the radar terminal. Speed is detected through the Doppler shift phenomena.
The system also includes an integrated weather radar operating across six levels (in accordance with the US National Weather Service standard), although only five levels can be used at any one time and are range dependant. The weather radar integrates three 12 second pulses to report a single 36 second weather map (3).
The ARSR-4 is designed to track up to 800 airborne targets and an additional 200 non-aircraft returns per 12 second scan (3), with no more than 196 false returns (5). The ARSR-4 is designed as a low maintenance unattended station (with a mean time before failure of 1500 h it only needs servicing every 2 months), utilising dual frequency hopping to avoid jamming. Additional Performance parameters are tabulated below.
ARSR-4 (AN/FPS-130) Air Surveillance Radar
Criteria Tabulated Performance (Reported) Calculated Performance How Calculated
Transmission
Beam width 2.2?? Vertical
1.41?? Horizontal (stacked)
Pulse Length 150 ??s 2.15 ??s From Range Resolution
Frequency
Operating 1.2Ghz ‘ 1.4 Ghz
PRF 288PPS
Coverage
Range 463km 521 Max range from PRF
Azimuth 360??
Elevation -7?? – +30??
Detection Altitude 30480 393km Trigonometry, calculated range and given elevations
Scan Rate Rotational 5 RPM
Side Lobes -35db near
-40db far
Track Capacity 1000 (800 aircraft plus 200 other)
Polarisation Linear or circular
Accuracy
Azimuth 0.176??
Resolution
Elevation 1.5?? 1.2km
Range 323m 12km
Azimuth 1.6km at 512km, Algebra using given values
Operation
Antenna gain 35db Transmit
40db Receive
MTBF 1500hr
Power
Watt 65kW Peak
3.5kW Average
81kW Transmit Average Power Transmit Power relationship
Table 2: Tabulated data for the ARSR-4 (AN/FPS-130) Air Surveillance Radar
Some discrepancies have been noted between the claimed or reported value and the calculated values. These discrepancies will be as a result of the ideal scenario that is assumed when calculating the calculated values compared to the complete calculations which would have been used to provide a base mark against for the measurements in the operational testing and evaluation. The values which are missing to conduct complete calculations using the radar rage equation include the temperature tolerances and noise variances amongst others. These discrepancies will be further exacerbated by a requirement for security and the protection of intellectual property. The calculated values are within the reasonable tolerances that one would expect, that is there is a difference in range and accuracy but it is not significant. There is a significant difference in the calculated and reported pulse length. It is highly likely the system is using pulse compression and the reported values are those which result from the pulse compression. The claimed accuracy of a 1m target fails to tell the prospective buyer much about the system. This is true due to the inability of the system to resolve these target at the maximum range. That is although the system will detect a return it will not be able to determine if the return is a single target or a group of targets close together. .
The strength of the ARSR-4 lies in its ability to truly interface with other systems to form a complete radar image. This allows the system to capitalise on one aspect of radar which would cost performance in another, this is demonstrated by the low PRF which allows the system to have a large unambiguous range and detect small returns at a cost of an ambiguous Doppler measurement, meaning it will produce highly accurate range but ambiguous radial velocity. The joint nature of this systems has likely been a driving factor in the selection of PRF, the US Air Force will have wanted to detect targets with a radar cross section between 0.5 and 0.005m2 (Cruise Missiles and Gen 5 Fighter) to allow early response. Whereas the Federal Aviation Administration will need to detect and control small aircraft its focus would be on Cabin Cruisers with a radar cross section of approximately 10m2. As we can see the disparity in detection threshold is vast and as such significant compromises would have had to be made to reach a joint agreement.
AN/TPS-59(V)3 Tactical Radar
Country of Origin: United States of America
Manufacturer: Lockheed Martin
Role: ‘To provide long-range surveillance of a tactical airspace to the Tactical Air Operations Centre’ (7).
Radar Design: The AN/TPS-59(V)3 Tactical Radar is a long range 3D D-Band (1-2 Ghz) phased array radar. The system is trailer mounted on a number of vehicles. One vehicle carries the shelter which contains all the display consoles and the radar processors. An additional vehicle is required to tow the trailer mounted phased array antenna. The (V)3 standard allows the AN/TPS-59(V)3 to simultaneously queue automated defences such as the Hawk Automatic Missile System (7). The system is designed to track a 1m2 radar cross section target traveling at up to Mach 4 (1320ms-1 or 4752kmh-1) (7). This is an impressive number as the system will give a 560s warning of an inbound ballistic missile traveling at Mach 4 using the reported maximum radar range of 740km, plenty of time to queue automatic missile defences or manual defences as well as move troops from the calculated impact area. An additional function includes an identify friend or foe feature.
The radar is based on a solid state RF amplifier which similar to the ARSR-4 allows it to operate at low voltage however it will also produce excess heat which will cause significant problems for a mobile tactical unit such as the AN/TPS-59(V)3. No method of cooling the unit was made apparent. An additional advantage in a tactical environment is the reduction in a requirement equip the unit with a general electrician to advice on electrical repairs, instead the unit can train a specialist electrician to work throughout the radar system, reducing the crewing requirements by 1 person.
The radar is capable of two waveforms to conduct surveillance; a short interval ranging from 5.5km to 185km and a long range interval ranging from 185 to the radar limit. The antenna produces 8 pencil beams to scan the long range zone and 11 to scan the short range zone (7). This will result in a greater accuracy within the short range zone. From the performance data released it has been determined the unit utilises significant pulse compression, which would allow the unit to increase resolution whilst reducing clutter returns.
The radar uses a planar array antenna with 54 active elements (rows), it is mounted on a rotating platform approximately 2m above the ground. The foot print o the antenna is 9.1m high by 4.9m mounted on a trailer which is towed into place. It takes roughly 3 hours to deploy the antenna and connect it to the shelter and an additional 30 mins for the radar system to respond. In addition to the radar planning considerations that must be taken into account extra considerations regarding deployment response time, the methods of moving the system into the desired location and the security which must accompany the convoy and then remain in place with the established radar must be planned for. This would be a significant burden on any operational commander particularly as the system would be considered a high value target and there was no mention of air portability.
Although the radar does not include a weather mapping function it does include a function which automatically adjusts the radars power outputs to counter prevailing weather conditions (7). The radar’s tabulated data is below.
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AN/TPS-59(V)3 Tactical Radar
Criteria Tabulated Performance (Reported) Calculated Performance How Calculated
Transmission
Beam width 1.375?? Horizontal
2.553?? Vertical Relationship to antenna size
Pulse Length 287ns Relationship to Range Resolution
Frequency
Operating 1.215 1.4 Ghz
PRF 833.21khz Relationship to Power
Coverage
Range 550km (Air Breathing), 740km (Ballistic)
Azimuth 360??
Elevation -2?? – +20?? (Air Breathing)
-2?? – + 60?? (Ballistic)
Detection Altitude 30480m (Air Breathing)
304800m (Ballistic)
Scan Rate Rotational 6RPM
12RPM
Accuracy
Range 30.5m (Air Breathing @ 80nm)
Azimuth 0.1718 (Air Breathing @100nm)
Height 304.8 (Air Breathing @100nm)
Resolution
Elevation 13.6km Relationship to beamwidth
Range unknown 17.8km Relationship to beamwidth
Azimuth 2.2km Relationship to beamwidth
Operation
Duty Cycle 25%
Deployment Time 240min
Respond Time 30min
MTBF 2000hr
Power
Watt 46kw Transmit
11kw Average
Table 3: Tabulated data for the AN/TPS-59(V)3 Tactical Radar
The overall success of the AN/TPS-59(V)3 has led to a number of other systems designs being based off it. Two include the AN/FPS-117 fixed site radar and the AN/TPS-59M (7), the latter is a mobile radar system with a significantly reduced foot print but similar performance.
The calculations have identified some discrepancies in the data that is reported on the AN/TPS 59(V)3, most importantly is the extremely high PRF calculated using the range resolution to find the pulse width and then the relationship between average power, peak power, pulse width and the PRF to determine a PRF. This will not represent a true value as the system must use pulse compression to achieve the high resolution and low pulse width reported.
The true strength of the AN/TPS-59(V)S is in its ability to track an extremely fast moving target with a relatively small radar cross section at long range, allowing countermeasures to be queued or assets moved out of the danger area. Although it suffers a long establishment time when compared to other mobile tactical units, this time is still not preclusive when it is considered as an operational or strategic asset rather than a tactical emplacement. As discussed this radar relies on a solid state RF amplifier, although it is the opinion of the author that moving parts are opportunities for things to go wrong and an increased maintenance overhead, in this instance the excess heat generated will pose an issue if it is not correctly cool, limiting the locations that the system can be emplaced.
TRD-1235
Country of Origin: Russia
Manufacturer: P??emyslid Institute of Telecommunications
Role: The TRD-1235 is a fixed mobile long range air defence command and control system, utilised for plot and track with no reported weapons queuing capability.
Radar Design: The TRD-1235 is a D Band (1-2 Ghz) 3D coherent, mobile radar, consisting of a transportable tower antenna, transmitting unit and operators shelter. The radar also incorporates auxiliary antennas allowing the system to transmit on a cosec2 radiation pattern but receive on a planar array antenna. The system can be operated on site or remotely. It has a mechanically scanned azimuth (8). The TRD-1235 is towable on a 6m or 12m vehicle or is air transportable by an aircraft the size of a C-130 Hercules.
The TRD-1235 is fundamentally different from the previous two radars as it uses a traveling wave tube and three stage amplitron (cross field amplifier) as the amplification method for the operating frequency, only using the solid state RF generator as the source. This type of amplification enjoys a high efficiency rate, low levels of additional noise, as well as allowing the system to simply turn off any stage of a multi stage amplifier, if it requires lower energy levels, as the amplitron will simply act as an additional section of wave guide (9).
The TRD-1235 uses a compression pulse which allows it to detect weak target signals and reduce the required power output, limiting is vulnerability to electronic warfare countermeasures. In addition the TRD-1235 also employs advanced signal processing and varying types of Electronic Counter Counter Measures in attempt to keep the unit operational at a high level of reliability and undetected.
The TRRD-1235 utilises two antennas a main antenna and a secondary antenna. The main antenna, utilised for the receiver is of planar array design, designed to work in a stationary ray domed tower with a secondary antenna utilised to provide the transmission signal. The secondary antenna is a dipole arranged in 40 in-phase rows providing a cosec2 radiation pattern. The system is designed for continuous operation from different power sources (8).
Specific to this radar is the addition of excess transmission elements allowing maintenance to occur without the radar system being switched off.
The TRD-1235 costs approximately $20 million per unit.
AN/TPS-59(V)3 Tactical Radar
Criteria Tabulated Performance (Reported) Calculated Performance How Calculated
Transmission
Beam width 1.6?? (Horizontal) 0.52?? (Vertical) Relationship to antenna
Pulse Length 1.33??s Relationship to Range Resolution
Frequency
Operating 1 ‘ 2 Ghz
PRF 13.125khz Relationship to Power
Coverage
Range 440km
Azimuth 360??
Elevation 30??
Detection Altitude 30000m
Scan Rate Rotational 6RPM
12 RPM
Accuracy
Range 30m
Elevation 0.2??RMS
Resolution
Elevation 2.5?? 19.1 km Relationship to beamwidth
Range 200m 12 km Relationship to beamwidth
Power
Watt 7kw Average
400kw Peak
Table 4: Tabulated data for the TRD-1235 Fixed Mobile Long Range Air Defence Command and Control System
The TRD-1235 appears to have released the most reliable performance specifications of the three radars reviewed. This was of surprise as the unit is still in use as a tactical radar establishment in many eastern bloc country’s today. Another surprise was this radar is reported to work within the NATO air defence ground environment (8), this may explain the reliability of the performance specification. Some western NATO countries may have chosen to publish these details allowing western arms manufactures to defeat the system if required to when it is confronted as a threat system in possible conflict with Russia.
Overall all the systems reviewed provided performance details which had variations to those which were calculated. This is a reasonable expectation as individual companies desire to hold onto intellectual property and industrial secrets. This will pose a potential problem to prospective buyers as the complete and true performance specifications may not be available for initial / short list selections, possibly resulting in the best solution to a given problem being prematurely cut from candidate systems. This in turn poses a problem to the industry itself, in how much information is suitable and how much is too much. Similarly security agencies and militaries alike do not want to have the exact performances of systems published allowing the adversary to design a system to defeat it.
It was found that the most common performance detail which is withheld is PRF and pulse width, this may be due to these being the criteria which define the range resolution and unambiguous range of the radar systems being reviewed. This was further made difficult by systems possibly using pulse compression without declaring it. The method of signal processing was also not discussed in detail, this would need to be reviewed in detail as this processing is what is improving the performance specifications of the reviewed radars. It was also uncommon for the radar system to have its antenna gains or efficiencies reported. Where it was possible to reverse calculate the efficiencies they ranged between 20-50%. This could be due to the antennas being utilised as part of a larger system so the antenna a subsystem would be optimised for the overarching system rather than as a standalone antenna. Overall during the research process it was noted that tactical land systems tended to have a larger degree of secrecy surrounding them, even when compared to the strategic naval units.
Finally it was determined that the manufacturers glossy brochures where only suitable for wetting the appetite for a given system. They tended to give the best performance rather than an average system performance, which is to be expected. A significant amount of research and test would be required, including a thorough review of performance specifications and site testing as a minimum, prior to any decision being made on the acquisition of a specific system. As a result the evaluation process of a candidate system will be a resource and time expensive undertaking regardless of whether the system is commercial / military off the shelf or purpose designed.