Air Defense

91N6A surveillance and tracking radar

Also known as
  • 91N6A
  • 91N6
  • 91N6A(M)
  • 91N6M
  • 91N6E
  • Big Bird radar
  • S-400M radar
  • S-500 acquisition and battle-management radar

The 91N6A is a Russian 91N6-family mobile surveillance and tracking radar tied to Almaz-Antey's long-range air-defense architecture. Open sources describe the 91N6 family as the S-band Big Bird acquisition radar for the S-400 Triumf, with the 91N6A identified as a modernized S-400M form and the 91N6A(M)/91N6M discussed as a later S-500 acquisition and battle-management radar.

91N6A surveillance and tracking radar, Mobile air-surveillance and battle-management radar, Air Defense
Image source: 91N6
Profile / Specs

Profile

Origin
Russia
Built by
Almaz-Antey
Type
Mobile air-surveillance and battle-management radar
Service note
Modernized 91N6-family radar associated with S-400M and later S-500-family architecture in open sources
Designer
Almaz-Antey / NIIIP radar design lineage in open-source descriptions
Designed
91N6A described by Radartutorial as a modernization developed in the mid-1980s
Produced
Not publicly confirmed for the 91N6A subtype
Number built
Not publicly confirmed
Developed from
64N6E / Big Bird radar family

Specifications

Radar family
91N6 Big Bird S-band surveillance and tracking radar family
Public subtype
91N6A, described as a modernized S-400M form in Radartutorial; 91N6A(M)/91N6M appears in S-500 open-source descriptions
Role
Detects and tracks aerodynamic and ballistic targets and provides radar information to the air-defense command post in the export 91N6E description
Frequency band
S band; Radartutorial lists 2.9-3.3 GHz for the 91N6 family
Instrumented range
600 km listed by Radartutorial for 91N6-family data; Air Power Australia lists 640 km for the 91N6A(M) S-500 discussion
Targets tracked
Up to 300 targets in Radartutorial's 91N6-family description
Antenna
Back-to-back phased-array antennas with scan modes including continuous rotation, sector view, stopped antenna drive, and added antenna tilt in Radartutorial's description
Associated systems
S-400/S-400M family, export 91N6E within S-400, and 91N6A(M)/91N6M in S-500 open-source architecture descriptions
Radar Role

The 91N6 family is described as the Big Bird S-band search radar layer in Russian long-range air-defense systems. The radar is separate from the engagement radar: it builds the long-range air picture, tracks targets, supports identification, and passes radar information to command-post elements that can cue fire-control radars and launch units.

Primary function

Long-range surveillance, target tracking, and battle-management radar information for S-400/S-500-family air-defense architecture.

Public subtype caution

Open sources distinguish 91N6, 91N6A, 91N6E, and 91N6A(M)/91N6M, but detailed subtype differences are not consistently public.

Source references: 91N6; S-400 "Triumph"; Defending Mother Russia's Skies.

Variants

Open sources use the 91N6 designator across domestic, export, and later modernized Big Bird radar forms; public descriptions do not always separate 91N6A, 91N6E, and 91N6A(M) details cleanly.

VariantConfigurationDesignation notes
91N6Baseline Big Bird surveillance radar

Radartutorial describes 91N6 as a surveillance and tracking radar for the SA-21/S-400 family, derived from earlier Big Bird architecture.

Sources: 91N6

91N6AModernized S-400M form

Radartutorial identifies 91N6A as a modernization for S-400M Triumf systems.

Sources: 91N6

91N6EExport S-400 radar system

Rosoboronexport lists the 91N6E radar system in the S-400 export set and describes it as detecting and tracking aerodynamic and ballistic targets while feeding radar information to the 55K6E command post.

Sources: S-400 "Triumph"

91N6A(M) / 91N6MLater S-500-family acquisition and battle-management form

RUSI and Air Power Australia describe the S-500 ensemble as including a 91N6A(M) air-surveillance and battle-management radar, with Air Power Australia cautioning that public detail is insufficient to infer design changes from the baseline 91N6.

Sources: Defending Mother Russia's Skies, Almaz-Antey S-500 Triumfator M

Air-Defense System Context

The 91N6A page is treated as a component record because the radar's public conflict record is normally reported through complete S-400 or S-500 batteries rather than through a standalone radar subtype.

Compatible itemItem typeCompatibility evidence
S-400 Triumf, Long-range mobile surface-to-air missile system, Air DefenseS-400 TriumfLong-range surface-to-air missile system

Rosoboronexport's S-400 export description lists the 91N6E radar system as the search-and-tracking radar that detects aerodynamic and ballistic targets and provides radar information to the 55K6E command post.

Sources: S-400 "Triumph"

Why the radar matters

The radar supplies the long-range air picture and battle-management track data that lets the broader S-400/S-500 family cue command posts and engagement radars.

Sources: 91N6, Defending Mother Russia's Skies

Timeline

91N6A surveillance and tracking radar Key Events

  1. S-400 service-entry context

    CSIS Missile Threat lists the S-400 Triumf entering Russian service in 2007, providing the parent architecture for the 91N6-family radar role.

    Sources: S-400 Triumf

  2. S-500 radar architecture discussed

    RUSI described the expected S-500 radar ensemble as including a 91N6A(M) air-surveillance and battle-management radar enhanced from the 91N6A associated with S-400.

    Sources: Defending Mother Russia's Skies

Related Weapon Systems
1L125 Niobium-SV, Mobile VHF three-coordinate air-defense surveillance radar, Air DefenseAir Defense1L125 Niobium-SVMobile VHF three-coordinate air-defense surveillance radarThe 1L125 Niobium-SV is a Russian mobile VHF/meter-band, three-coordinate radar built for ground-forces air defense and developed by NNIIRT within the Almaz-Antey group. Rosoboronexport's 1L125E export profile describes a 5-500 km, 360-degree surveillance radar for detecting, tracking, identifying, and reporting aerodynamic and ballistic targets, including low-observable aircraft; Ukrainian and sanctions-derived records identify Niobium-SV radars in Russian service during the Russia-Ukraine war.
1L13-3 Nebo-SV, Mobile VHF two-coordinate air-surveillance radar, Air DefenseAir Defense1L13-3 Nebo-SVMobile VHF two-coordinate air-surveillance radarThe 1L13-3 Nebo-SV is a Soviet/Russian mobile meter-band radar for ground-forces air defense, built to search for aircraft, helicopters, UAVs, and other air targets and pass range-and-bearing data to command posts or missile batteries. It is a two-coordinate predecessor to the 1L119 Nebo-SVU: sources describe it with a 72-element VHF antenna array, separate IFF interrogator, six-person crew, and fighter-target detection figures reaching roughly 350 km at high altitude.
2K11 Krug / SA-4 Ganef, Tracked medium-range surface-to-air missile system, Air DefenseAir Defense2K11 Krug / SA-4 GanefTracked medium-range surface-to-air missile systemThe 2K11 Krug, NATO reporting name SA-4 Ganef, is a Soviet tracked medium-range surface-to-air missile system built around 2P24 launchers, 3M8-series missiles, and separate acquisition and guidance radars. In the 2020 Nagorno-Karabakh war it appeared on the Armenian and Artsakh side as legacy area air defense, but reporting from CSIS and Oryx shows it was vulnerable in a battlespace dominated by Azerbaijani UAVs and loitering munitions.

Sources

91N6Publisher: Radartutorial | Note: Specialist radar reference supporting 91N6-family role, S-band frequency, target-tracking count, instrumented range, antenna layout, scan modes, 91N6A modernization note, and image provenance/licensing context. | Accessed: 2026-07-02S-400 "Triumph"Publisher: Rosoboronexport | Note: Official export product page supporting the 91N6E radar's S-400 role, target-detection and tracking function, nationality-determination function, and radar-information feed to the 55K6E command post. | Accessed: 2026-07-02S-400 TriumfPublisher: Center for Strategic and International Studies Missile Threat | Note: Supports the S-400 parent-system context, Russian origin, SA-21 reporting name, 2007 service-entry context, and Almaz-Antey background. | Accessed: 2026-07-02Defending Mother Russia's SkiesPublisher: Royal United Services Institute | Note: Supports S-500 radar-ensemble context, including the 91N6A(M) air-surveillance and battle-management radar and its relationship to the 91N6A radar accompanying S-400. | Accessed: 2026-07-02Almaz-Antey S-500 Triumfator MPublisher: Air Power Australia | Note: Supports specialist S-500 architecture context for the 91N6A(M) Big Bird acquisition and battle-management radar, while noting the limited public detail on design changes from baseline 91N6. | Accessed: 2026-07-02