{"id":1095,"date":"2026-06-24T03:38:07","date_gmt":"2026-06-24T03:38:07","guid":{"rendered":"https:\/\/planetary-gearboxes.com\/?p=1095"},"modified":"2026-06-24T03:38:07","modified_gmt":"2026-06-24T03:38:07","slug":"slewing-drive-planetary-gearbox-for-radar-antennas","status":"publish","type":"post","link":"https:\/\/planetary-gearboxes.com\/ceb\/slewing-drive-planetary-gearbox-for-radar-antennas\/","title":{"rendered":"Slewing Drive Planetary Gearbox for Radar Antennas"},"content":{"rendered":"
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Korea Ever-Power \u00b7 Application Engineering \u00b7 Radar and Antenna Systems<\/p>\n

Slewing Drive Planetary Gearbox for Radar Antennas \u2014 0.02 Degrees of Pointing Accuracy, 24 Hours a Day, for 20 Years<\/h1>\n

Every other slewing drive in this series measures precision in degrees. Radar antenna slewing drives measure precision in millidegrees<\/strong> \u2014 0.01 to 0.1 degrees \u2014 because a 0.1-degree pointing error on a 12-metre dish aimed at a satellite 36,000 km away misses the target by 63 kilometres<\/strong>.<\/p>\n

Browse Slewing Drive Planetary Gearboxes \u2192<\/a><\/p>\n<\/div>\n<\/section>\n

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Five Types of Antenna That Rely on Slewing Drive Planetary Gearboxes<\/h2>\n

Ang slewing drive planetary gearbox<\/a> is the positioning mechanism for every steerable antenna larger than approximately 1 metre diameter \u2014 from airport surveillance radars to deep-space communication dishes. Each antenna type places different demands on the drive, but all share the requirement for angular precision far beyond any construction or energy application.<\/p>\n

\n\n\n\n\n\n\n\n\n\n
Antenna Type<\/th>\nDish (m)<\/th>\nPointing (deg)<\/th>\nKatulin<\/th>\nDuty<\/th>\n<\/tr>\n<\/thead>\n
Satellite Earth Station<\/td>\n3 \u2013 15<\/td>\n0.01 \u2013 0.05<\/td>\nVery slow (tracking)<\/td>\n24\/7 continuous<\/td>\n<\/tr>\n
Airport Surveillance<\/td>\n4 \u2013 10<\/td>\n0.1 \u2013 0.3<\/td>\n4 \u2013 15 rpm (continuous)<\/td>\n24\/7 continuous<\/td>\n<\/tr>\n
Weather Radar<\/td>\n3 \u2013 8<\/td>\n0.1 \u2013 0.5<\/td>\n2 \u2013 6 rpm<\/td>\n24\/7 continuous<\/td>\n<\/tr>\n
Military Tracking<\/td>\n1 \u2013 6<\/td>\n0.005 \u2013 0.02<\/td>\nVariable (0 to 60 deg\/s)<\/td>\nIntermittent<\/td>\n<\/tr>\n
Radio Telescope<\/td>\n10 \u2013 100<\/td>\n0.001 \u2013 0.01<\/td>\nSidereal rate (0.004 deg\/s)<\/td>\nNightly observation<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

\"Slewing<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/section>\n

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Backlash Is the Enemy \u2014 Why Antenna Drives Require Near-Zero Gear Play<\/h2>\n
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In a construction crane slewing drive, 10 to 15 arcminutes of backlash is acceptable \u2014 it produces a few centimetres of hook position uncertainty at the boom tip, easily accommodated by the operator. In a radar antenna, backlash directly translates to pointing error \u2014 and pointing error means the antenna beam misses its target.<\/p>\n

For a satellite earth station tracking a geostationary satellite at 36,000 km: a 0.1-degree pointing error (6 arcminutes) displaces the beam centre by 63 km at the satellite \u2014 far outside the satellite transponder beam width. The signal is lost. For a military fire control radar: a 0.02-degree error (1.2 arcminutes) at 50 km range displaces the tracking point by 17 metres \u2014 enough to miss a small target entirely.<\/p>\n

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< 1<\/div>\n
arcminute total system backlash for satellite tracking. The slewing drive itself must contribute less than 0.5 arcminutes \u2014 the remaining budget is consumed by the bearing, the pedestal, and the structural deflection of the antenna.<\/div>\n<\/div>\n
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< 0.3<\/div>\n
arcminutes for military tracking radars. Achieved through preloaded dual-pinion anti-backlash gear arrangements \u2014 two pinions meshing with the same ring gear in opposing directions, spring-loaded against each other to eliminate all play.<\/div>\n<\/div>\n<\/div>\n
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Backlash management strategy \u2014 dual-pinion anti-backlash:<\/strong> The most effective approach for high-precision antennas uses two slewing drives meshing with the same ring gear, each loaded against the other by a torsion spring or a constant-pressure hydraulic cylinder. One drive pushes clockwise, the other pushes counter-clockwise. The spring force keeps both pinions in constant contact with their respective tooth flanks \u2014 eliminating the dead zone that single-pinion systems exhibit during direction reversal. This dual-pinion arrangement is standard for satellite earth stations and military tracking radars, and adds 60 to 100% to the slewing drive cost \u2014 a premium that is justified by the pointing accuracy improvement.<\/p>\n<\/div>\n<\/div>\n

\"Planetary<\/p>\n
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Planetary gear mesh. Radar antenna drives use DIN Class 4 to 5 gears with grinding finish \u2014 2 to 3 quality grades higher than construction drives \u2014 to achieve the sub-arcminute backlash that pointing accuracy demands.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/section>\n

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Continuous Rotation Duty \u2014 Airport Radars That Spin 24\/7 for 20 Years<\/h2>\n

An airport surveillance radar (ASR) rotates continuously at 12 to 15 rpm \u2014 one full revolution every 4 to 5 seconds \u2014 24 hours a day, 365 days a year, for 15 to 20 years between major overhauls. This is the most demanding continuous-rotation duty any slewing drive faces. In 20 years, the azimuth slewing drive completes approximately 63 to 158 million revolutions \u2014 orders of magnitude more than any construction or energy slewing drive.<\/p>\n

At 15 rpm, each planet gear tooth in a 3-stage planetary reducer with a 600:1 ratio completes approximately 9,000 revolutions per minute at the sun gear. The bearing and gear tooth life calculations for this continuous high-speed duty are fundamentally different from the intermittent, low-speed duty of construction and energy slewing drives. The L10 bearing life must be calculated using continuous-duty load spectra, not the intermittent-duty spectra used for cranes and wind turbines.<\/p>\n

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The lubrication challenge of continuous rotation:<\/strong> At 15 rpm continuous, the slewing drive oil temperature stabilises at 40 to 60 degrees C above ambient \u2014 year-round. In a tropical airport installation at 40 degrees C ambient, the internal oil temperature can reach 100 degrees C continuously. The oil must maintain viscosity, film strength, and oxidation resistance at this temperature for 4,000 to 8,000 hour oil change intervals. Synthetic PAO (poly-alpha-olefin) oils are standard for continuous-rotation radar drives \u2014 mineral oils oxidise too rapidly at these sustained temperatures.<\/p>\n<\/div>\n<\/div>\n

\"Slewing
\n\"Precision<\/p>\n
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Top: Continuous-rotation slewing drive application. Bottom: Precision gear grinding \u2014 radar drives require the highest gear quality grades (DIN 4 to 5) for 20 years of uninterrupted rotation.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/section>\n

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\"Slewing<\/p>\n
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Radar antenna installations range from compact 1-metre military tracking dishes to 100-metre radio telescopes \u2014 all positioned by slewing drive planetary gearboxes with precision 10 to 1,000 times tighter than any construction application.<\/p>\n<\/div>\n<\/div>\n

\"Korea<\/p>\n
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Korea Ever-Power testing centre. Radar antenna slewing drives undergo backlash measurement to sub-arcminute resolution and continuous-rotation endurance testing before delivery \u2014 verifying both precision and durability simultaneously.<\/p>\n<\/div>\n<\/div>\n<\/div>\n

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Electromagnetic Compatibility \u2014 Why a Radar Antenna Drive Must Be Electrically Silent<\/h2>\n

A radar antenna receives signals as weak as -120 dBm (one billionth of a billionth of a watt). Any electromagnetic noise generated by the slewing drive motor, the encoder, or the drive electronics can couple into the antenna feed and mask the target signal. The slewing drive system must comply with EMC (electromagnetic compatibility) requirements that are orders of magnitude stricter than any industrial drive standard.<\/p>\n

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Motor Selection<\/div>\n

DC brushless motors are preferred over brushed motors because brush arcing generates broadband electromagnetic noise. Variable-frequency drives (VFDs) for AC motors must use shielded cables and filtered outputs to prevent switching noise from radiating into the antenna sidelobes. In extreme cases, hydraulic motors (which generate zero electromagnetic emission) are used \u2014 accepting the lower positioning precision of hydraulic drive in exchange for complete electromagnetic silence.<\/p>\n<\/div>\n

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Encoder and Feedback<\/div>\n

Position feedback encoders mounted on the slewing drive output must provide resolution matching the pointing accuracy \u2014 typically 18 to 22 bit (262,144 to 4,194,304 counts per revolution). These high-resolution encoders use optical or magnetic sensing and generate low-level digital signals that must be shielded from the motor power cables. The encoder mounting interface on the slewing drive must provide rigid, vibration-free attachment with zero-backlash coupling to the output shaft.<\/p>\n<\/div>\n

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Grounding and Shielding<\/div>\n

The slewing drive housing must provide a continuous electrical ground path from the motor frame through the gearbox housing to the antenna pedestal \u2014 preventing ground loops that generate noise currents. All cable entries must use shielded connectors with 360-degree shield termination. The slewing ring bearing must maintain electrical continuity between the rotating and stationary parts to prevent charge accumulation and discharge arcing across the bearing rollers.<\/p>\n<\/div>\n<\/div>\n<\/section>\n

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Three Failure Modes Unique to Radar Antenna Slewing Drives<\/h2>\n
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1<\/div>\n
Backlash growth from continuous high-speed rotation degrading pointing accuracy<\/div>\n<\/div>\n

Over 63 to 158 million revolutions (20 years of continuous airport radar duty), even DIN Class 5 gear teeth experience measurable profile wear. As tooth profiles wear, backlash increases from the delivery value (0.5 to 1.0 arcminutes) toward the replacement threshold (2 to 3 arcminutes). Once the backlash exceeds the antenna pointing error budget, the radar resolution degrades \u2014 targets that were previously separable merge into a single return, and the air traffic controller loses situational awareness. The backlash growth is gradual and undetectable without periodic measurement.<\/p>\n

Prevention: Measure backlash at every annual service. Trend the backlash growth rate. Replace the pinion when the trend projects backlash will exceed the pointing budget within the next service interval. For critical radars, use dual-pinion anti-backlash drives that compensate for wear automatically.<\/div>\n<\/div>\n
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2<\/div>\n
Wind gust overload exceeding the drive holding capacity during storm stow failure<\/div>\n<\/div>\n

Large radar dishes (6 to 15 metres) are effective wind catchers \u2014 a 12-metre parabolic dish in a 150 km\/h storm wind experiences a drag force of 80,000 to 150,000 N, producing overturning moments of 200 to 500 kN\u00b7m at the slewing bearing. The normal procedure is to stow the antenna (rotate the dish face-on to the wind and lock the brakes) before the storm arrives. If the storm arrives unexpectedly or the stow mechanism fails, the slewing drive must hold the dish in its current position against the full wind load. If it cannot hold, the dish rotates uncontrolled and the wind catches it broadside \u2014 generating forces that can bend the pedestal or rip the dish from its mount.<\/p>\n

Prevention: Specify the slewing drive planetary gearbox<\/a> wind stall torque for the survival wind speed (typically 200 km\/h for permanent installations). Implement automatic wind-stow at 80 to 100 km\/h wind speed. Test the stow mechanism at every monthly maintenance visit.<\/div>\n<\/div>\n
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3<\/div>\n
Electromagnetic interference from motor or drive electronics corrupting the radar signal<\/div>\n<\/div>\n

A degraded motor brush, a loose shield termination, or a VFD filter failure can inject broadband noise into the antenna sidelobe response. This noise appears as false targets on the radar display \u2014 stationary clutter that masks real targets. Because the noise source rotates with the antenna, it appears as a consistent return at a fixed range \u2014 making it difficult to distinguish from a genuine target at the same position. Operators may not recognise the false return as drive-generated interference until a systematic EMC survey is performed.<\/p>\n

Prevention: Use brushless motors exclusively. Verify EMC compliance at commissioning and after any motor or drive electronics replacement. Include shielded cable and filtered power supply as mandatory specifications \u2014 not optional accessories.<\/div>\n<\/div>\n<\/div>\n<\/div>\n
\"ZR45
\n\"Korea<\/p>\n
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Top: ZR-series slewing drive \u2014 multi-stage precision planetary for antenna positioning. Bottom: Korea Ever-Power manufacturing facility with precision production lines for radar-grade drives.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/section>\n

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Slewing Drive Planetary Gearbox for Radar Antennas \u2014 Frequently Asked Questions<\/h2>\n
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What backlash is acceptable for a radar antenna slewing drive?<\/h3>\n

It depends on the antenna type. Satellite earth stations require less than 1 arcminute total system backlash (slewing drive contribution less than 0.5 arcminutes). Airport surveillance radars require 1 to 3 arcminutes. Weather radars tolerate 2 to 5 arcminutes. Military tracking radars require less than 0.3 arcminutes \u2014 typically achieved through dual-pinion anti-backlash configurations. For comparison, construction crane slewing drives typically have 10 to 15 arcminutes of backlash \u2014 10 to 50 times more than a radar antenna drive.<\/p>\n<\/div>\n

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How many revolutions does an airport radar slewing drive complete in its service life?<\/h3>\n

At 12 to 15 rpm continuous, 24 hours per day, 365 days per year, for 20 years: approximately 126 to 158 million revolutions. This is the highest revolution count of any slewing drive application \u2014 by a factor of 1,000 or more compared to construction or energy drives. The gear teeth, bearings, and seals must be specified for this extreme duty cycle. Standard construction-grade slewing drives are designed for 1 to 10 million revolutions \u2014 they would fail within 1 to 2 years of airport radar duty.<\/p>\n<\/div>\n

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What is the typical service life of a radar antenna slewing drive?<\/h3>\n

15 to 20 years for the planetary gearbox on continuous-rotation radars (airport, weather). 20 to 30 years for satellite earth station drives (which rotate very slowly). The oil change interval is typically 4,000 to 8,000 hours for continuous-rotation drives (synthetic PAO oil) and 8,000 to 16,000 hours for slow-rotation drives. The pinion may require replacement at 8 to 12 years on continuous-rotation drives \u2014 the gear mesh at the pinion-ring interface accumulates wear faster than the enclosed planetary stages.<\/p>\n<\/div>\n

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Can a solar tracker slewing drive be used for a radar antenna?<\/h3>\n

Only for very low-precision applications (weather monitoring antennas with pointing requirements above 1 degree). Solar tracker drives are designed for self-locking worm-gear stages at 40 to 65% efficiency \u2014 acceptable for once-daily sun tracking but too lossy for continuous-rotation radar duty. Solar drives also have backlash specifications of 5 to 15 arcminutes \u2014 5 to 50 times higher than radar requirements. For radar applications above the basic weather monitoring level, purpose-designed antenna slewing drives with precision planetary stages and anti-backlash provisions are essential.<\/p>\n<\/div>\n

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Does Korea Ever-Power supply precision slewing drives for radar and antenna applications?<\/h3>\n

Yes. Korea Ever-Power manufactures slewing drive planetary gearboxes for radar and satellite antenna positioning with backlash specifications from less than 0.5 arcminutes (single-pinion precision) to less than 0.2 arcminutes (dual-pinion anti-backlash). DIN Class 4 to 5 ground gears, synthetic PAO lubrication, high-resolution encoder mounting provisions, and EMC-compliant shielded housings are available. Continuous-rotation models for airport and weather radars (up to 20 rpm) and precision-tracking models for satellite earth stations (sidereal rate to 5 deg\/s) are both available. Provide the antenna diameter, pointing accuracy requirement, rotation speed, and duty cycle for a specification matched to the radar system performance requirements.<\/p>\n<\/div>\n<\/div>\n<\/section>\n

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Radar Antenna Slewing Drives \u2014 Millidegree Precision, Million-Revolution Durability<\/div>\n

Korea Ever-Power provides radar antenna slewing drive planetary gearboxes with sub-arcminute backlash, continuous-rotation ratings, and EMC-compliant housings. Provide your antenna type and pointing requirement for a precision specification.<\/p>\n<\/div>\n

View Slewing Drive Range \u2192<\/a><\/p>\n
sales@planetary-gearboxes.com<\/div>\n<\/div>\n<\/div>\n<\/section>\n

Editor: Cxm<\/p>\n<\/div>","protected":false},"excerpt":{"rendered":"

Korea Ever-Power \u00b7 Application Engineering \u00b7 Radar and Antenna Systems Slewing Drive Planetary Gearbox for Radar Antennas \u2014 0.02 Degrees of Pointing Accuracy, 24 Hours a Day, for 20 Years Every other slewing drive in this series measures precision in degrees. Radar antenna slewing drives measure precision in millidegrees \u2014 0.01 to 0.1 degrees \u2014 […]<\/p>","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_et_pb_use_builder":"","_et_pb_old_content":"","_et_gb_content_width":"","footnotes":""},"categories":[965],"tags":[],"class_list":["post-1095","post","type-post","status-publish","format-standard","hentry","category-application-and-technical-guid"],"_links":{"self":[{"href":"https:\/\/planetary-gearboxes.com\/ceb\/wp-json\/wp\/v2\/posts\/1095","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/planetary-gearboxes.com\/ceb\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/planetary-gearboxes.com\/ceb\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/planetary-gearboxes.com\/ceb\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/planetary-gearboxes.com\/ceb\/wp-json\/wp\/v2\/comments?post=1095"}],"version-history":[{"count":2,"href":"https:\/\/planetary-gearboxes.com\/ceb\/wp-json\/wp\/v2\/posts\/1095\/revisions"}],"predecessor-version":[{"id":1098,"href":"https:\/\/planetary-gearboxes.com\/ceb\/wp-json\/wp\/v2\/posts\/1095\/revisions\/1098"}],"wp:attachment":[{"href":"https:\/\/planetary-gearboxes.com\/ceb\/wp-json\/wp\/v2\/media?parent=1095"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/planetary-gearboxes.com\/ceb\/wp-json\/wp\/v2\/categories?post=1095"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/planetary-gearboxes.com\/ceb\/wp-json\/wp\/v2\/tags?post=1095"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}