Iran's Bavar-373: A Profile

Since the cancellation of the first S-300PMU-1 delivery by Russia in 2010, Iran vowed to develop a superior system, and the Bavar-373 was finally fully unveiled on Defence Industry Day on 22nd August 2019 after roughly 9 years of development.


A wholly indigenous system

Despite Russia finally delivering the S-300PMU-2 to Iran in December 2016, the Bavar-373 is commonly conflated with being simply a copy of the S-300. Iran had displayed numerous Bavar subsystems before the S-300PMU-2 delivery in December 2016, and even made a partial unveiling of numerous radars, missiles, and a restricted view of the launch cells in August 2016 - also on Defence Industry Day. Although Iran is suspected to have acquired an S-300PT system from Belarus, that is a 1980s-vintage system, with dated radars and 5V55K/R missiles up to a maximum range of just 90 km. While it is possible that Iran learnt some concepts and technologies by studying this system, any real relation between the S-300PT and the Bavar-373 is out of the question, not least because the Bavar-373 is far more capable, being closer to the S-300PMU-2 and S-400 in terms of performance and sophistication.

Not only does Bavar-373 sport AESA radars and a 200 km range missile in the form of Sayyad-4, but very clearly all these key subsystems look physically different and distinct from their foreign counterparts. Bavar-373 also has indigenous vehicles, and the missiles are launched directly ('hot launch') from square launch cells, rather than the gas ejection ('cold launch') system of the S-300's circular missile tubes.

To help clear up any confusion I made this handy comparison chart.

Comparison showing Bavar-373 and S-300 equivalent subsystems side-by-side: (Top to Bottom) TELs, Engagement Radars, Acquisition Radars, Battle Management Radars


Characteristics

While the Bavar-373 is an Iranian system, it certainly does take some conceptual nods from the S-300.

Bavar-373 is a large, top-of-the-line system, and therefore not as easily hidden as the Sevome Khordad system that shot down an American RQ-4 UAV in June. However, it is still highly mobile, with the large 10x10 Zoljanah acting as the TEL vehicle, and most radars and command and control (C2) equipment being mounted on the Zafar 8x8 vehicle. Both trucks are clearly off-road capable. This is an important capability as although Iran has a large road network, it means Bavar-373 can be deployed almost anywhere. The only 'semi-mobile' component of Bavar-373 is the large Meraj-4, which is a battle-management radar with a similar role to that of the 64N6E/91N6E 'Big Bird' radar. That is mounted on a semi-trailer pulled by a civilian type tractor truck. This is not so much of an issue though, with its long range allowing it to sit in a deeper position and therefore have greater security compared to the 'front-line' radars.

Meraj-4 Battle Management Radar

In reality the Meraj-4 is not strictly an integral part of Bavar-373. But it is closely related to the system and has appeared throughout Bavar-373's development, including alongside it in Bavar's partial unveiling in 2016. It is a higher tier IADS asset, and its job is to control large swathes of airspace providing information to systems in its vicinity. It is a large array size, S-band linear AESA  that can reportedly track up to 100 targets simultaneously. Along with this come advanced features that are detailed on a website called kowsartrading, which seems to be the successor to the short lived Iran Electronic Industries website. With ECCM capabilities including "Burn Through, SLB and SLC, Frequency Hopping, PRF Jitter, PRF Staggering, JATS, Pulse Compression, MTI, CFAR, Clutter Map, Low SLL Antenna," Meraj-4 should be a resilient radar.

Meraj-4 in full view in 2016

The latest iteration of Meraj-4, seen here in a new folded configuration, was present at the Army Parade in April 2019

Spec sheet for the Meraj-4 radar

Subsystems

The core of the battery-level Bavar-373 system is 1x Command and Control Vehicle, 2x Radars (Acquisition and Engagement), and up to 6x TELs, each carrying 4 missiles for a total of 24 missiles.

Bavar-373 command structure

Sayyad-4 Surface-to-Air Missile

The Sayyad-4 was first seen in 2014 in TV footage that displayed even some of the early iterations of Bavar-373's radar systems. At this time, it appeared as a very large white missile with باور-۳۷۳ (Bavar-373) just about visible on the body of the missile. It appeared alongside another new missile, the red Sayyad-3.


Sayyad-4 missile (right) in 2014


Sayyad-4 has a 200 km range, and maximum engagement altitude of 27 km. It is vertically launched from the Zoljanah TEL. It likely uses a form of Semi-Active Radar Homing, probably TVM (Track-Via-Missile) or SAGG (Seeker-Aided Ground Guidance). While ARH (Active Radar Homing) would have been an easier solution for a long range SAM, it would have been susceptible to jamming, and not been as effective against stealth targets (this is explained later in this blog post).


One of the more mainstream benefits of SAGG is that because guidance calculations can be calculated by both the missile and the ground radar, there is an added layer of redundancy that makes it more resistant to jamming. SAGG also tends to not give a missile launch warning to RWRs (Radar Warning Receivers), only letting them on that their aircraft is being illuminated. The inherent LPI (Low Probability of Intercept) characteristics of AESA radars enhance this advantage.

As of yet, it is unclear whether Bavar-373 has TVC (Thrust Vectoring Control) as in the S-300's 48N6 missile. It is unlikely to have this feature, as its ABM role is only secondary, and unlike the Russian system there is no requirement for Bavar-373 to engage low-flying cruise missiles at short range, which is part of the reason why the S-300 has a cold launch system and why TVC activates immediately after ejection to orient the 48N6 to fire in the right direction. Iran already has shorter range systems without VLS, like the Sayyad-2 and Sayyad-3 missiles, that are more suited to low-altitude/short-range interception.

UPDATE: According to an Iranian general appearing on TV, Bavar-373 does have TVC.

The Sayyad-4 missile (serial no. SD4AM M4A) at Bavar's official unveiling in August 2019

Comparison of Sayyad-4 (top) and 48N6 (bottom) missiles. The Sayyad-4 has a completely different fin assembly, and slightly more tapered nose.

Sayyad-4 making a sharp turn after launch


Unnamed X-band Radar

Judging by the small array size of this AESA, it can be judged that the pictured radar is an X-band radar. X-band radars are used as engagement radars in modern military systems like air defence systems and combat aircraft. There are few specifications for this radar, but in normal operation, this X-band radar would be able to engage conventional (non-VLO) aircraft out at ranges of 200 km on its own, engaging 6, guiding 12 missiles (so 2 missiles per target, ala S-300). This radar would likely be able to operate on its own against conventional targets, but for redundancy purposes. Against VLO aircraft it could have a special mode of operation in conjunction with the S-band radar which I will talk about later in this post.

One distinctive feature of this radar are the 4 possible additional arrays on the sides of the main array. It is unclear what purpose these have - they may be SLC (Side Lobe Cancelling) arrays, sub-arrays, or even data-link channels. If they are sub-arrays, then it is possible that the small main array of this X-band radar is deceiving. The inward angle of the sub-arrays suggests they could be creating an effect called constructive wave interference* to produce higher gain and effective higher range. This allows the radar to remain compact and have relatively low power levels compared to brute force PESA solutions like the 30N6 Tomb Stone/92N6 Grave Stone. The AESA TRMs of this radar allow electronic beam steering to align the radar waves to make use of this effect correctly. Though the main reason for lower required power requirements is the AESA configuration of the radar. Iran's defence minister said in an interview that this radar has 10,000 "elements" (TRMs).

*It is likely that these "sub-arrays" are just access hatches.

Bavar's X-band radar array, with main components highlighted. main array in Red, possible sub-arrays in Yellow, and IFF array in Blue.


Unnamed S-band Radar

The next radar is an acquisition radar, as it doesn't make much sense to have an X-band acquisition radar (much less to have 2 X-band radars). In addition to this its array size is noticeably larger, and added to the fact that Iran has been working on S-band AESAs for years now, it is reasonable to assume this next radar - the Acquisition radar - operates in the S-band. From this we can judge which of the official statistics apply to this S-band radar. Since it is the Acquisition radar, the specifications are likely to include the maximum targets detected (300), the range of detected targets (320 km), the range of tracked targets (260 km), and the maximum tracked targets (60). However, it is expected that the X-band radar would have its own limited acquisition and tracking (of course) capabilities for the sake of redundancy.

Some of these statistics (the last one, if at all) may belong to the X-band radar, but Iran did not bother to separate the statistics so there's a bit of informed guesswork involved in doing this myself.
Against normal non-VLO targets, the S-band radar works how any acquisition radar works. It may not even be needed if the Meraj-4 is free to support the battery from the back line. However, its smaller size and therefore superior mobility on the Zafar 8x8 truck makes it a valuable battery-level asset on the front line and earns it a place in the Bavar-373 system. This S-band component makes Bavar-373 a dual-band system (similar to the latest versions of the Aegis Combat System). This has positive implications for its ability to be used against stealth aircraft.

Very prominent is a large IFF-antenna on top of the radar array, a display of the radar's high requirement for tracking range and numbers. It is a similar case on the X-band radar.

Bavar's S-band radar array. Red area is the main array, blue area is the IFF array.


Command and Control (C2) Vehicle

The C2 cabin sits atop a 6x6 truck that seems slightly larger than the usual 6x6s Iran uses for its Talash and 15 Khordad TELs and radar vehicles. While we have not got a view of the inside of the cabin, the use of a dedicated C2 vehicle (in contrast with medium-range systems like 15 Khordad that have the C2 cabin with the radar cabin) is an indication of the sophistication of this part of Bavar-373. Curiously, there are no visible antennas on the C2 vehicle for long-range communication - this is not surprising however, as Iran (unlike Russia) deploys battery vehicles at one site rather than scattered over a wide area.

Foreground: Bavar's C2 vehicle

Zoljanah 10x10 TEL

Zoljanah was first seen in September 2012, sporting an unusual angular cab. In 2014 the current design was shown, with a much more sober cab design that was practically ahead of the front axle, instead of on top of it like the first iteration. This was possibly to create more room for an extra equipment behind the cab, seemingly for power generators and storage. Even when carrying a 30 ton payload, the 10x10 chassis is fully off-road capable. The quad missile canisters (twin in display and testing models) are approximately 7.5 metres long, and extend to a vertical position for launch. As the missiles are 'hot launched', there is an integrated blast deflector below the canisters, presumably to prevent too much dust being thrown up, or to protect any prepared surfaces that the Zoljanah TEL may be mounted at with its large hydraulic jacks. Possibly the most unusual thing about Zoljanah is that it needs a 5th axle at all - comparable vehicles for the S-300 need only 4, however the most modern versions including the S-400 also use semi-trailers with 5 axles. Such a long vehicle potentially has additional space for growth if Iran needs to mount larger missiles on it.

Zoljanah's 2012 iteration (top) and current design (bottom)

Rear of the Zoljanah TEL with quad missile canisters and blast deflector visible


Zafar 8x8 Radar Vehicle

Zafar was first shown in 2014. With a payload of 24 tons, probably the only thing preventing Zafar from being a TEL itself is the lesser length compared to Zoljanah. It is also fully mobile like the Zoljanah. The radars that can be mounted on this vehicle have a full 360° of rotation, with storage bins and other equipment supporting them. Each radar vehicle also has a command cabin at the rear, all equipped with beefy air conditioning units. The interior of these cabins is yet to be shown.

Zafar at its 2014 unveiling


Development

In the test-fire videos (likely from some years ago), we see several differences with the 'final' versions of Bavar:
  • None of the radars have their sub-arrays, additional equipment, or IFF antennas. Either these were still being developed, or were not required for the that testing phase.
  • The C2 cabin for the whole system sits on the ground between the radar vehicles, not mounted on any vehicle.
  • The Sayyad-4 missile is Red, likely for better visibility in cameras capturing the test.
  • The Zoljanah TEL only has 2 missile canisters, instead of 4 on the final version. These canisters are also slightly shorter, so that the missile tips are pointing out of them before launch. This has been observed in tests of Sayyad-2 and -3 missiles, likely to preserve the canisters or just out of not needing them for the test.

Mode of Operation versus Stealth Targets

Now we get to the special 'anti-stealth' feature I had been referring to earlier.

If Bavar uses a SAGG/TVM guidance method as expected, the presence of a separate S-band acquisition radar points to what is called a bi-static radar arrangement for engaging stealth targets. The S-band radar may not necessarily partake in this directly, but is still essential for its operation.

Bi-static arrangements work by placing a radar receiver closer to the target than the emitter, allowing it to pick up the signal without the signal having to return to the emitter. This is advantageous because when the receiver is closer to the target, it has a higher chance of picking up a weak signal or a more accurate one. The problem arises when X-band tries to illuminate a stealth target - it does not generate a return at anything greater than short ranges, as most stealth aircraft are optimised against the X-band, owing to its accuracy and therefore wide use in engagement radars. That's where bi-static operation comes in.

The idea is that the better anti-stealth performance of the S-band radar will allow it to detect the stealth aircraft at relatively long range, further aided by higher-tier IADS assets like the S-band Meraj-4 and VHF Matla ul-Fajr 3. The missile is fired, with target coordinates fed into its INS and updated periodically via a datalink. If the missile has a dual-band SAGG receiver (aka one that receives both X-band and S-band radar waves), it can be guided more accurately (with the bi-static effect) if the S-band radar has some illumination capability. This however is not essential, but does make the system more robust.

But S-band radars are typically not accurate enough to guarantee a kill - that's why X-band radars are used in engagement radars. But as we know, X-band radars are not usually effective against stealth aircraft. Under normal circumstances, the system can see the target, but not kill it.

So once the S-band radar guides the missile to the terminal stage - within about 5-10 km - the interception switches to X-band. Within 5 km the missile's radar receiver will likely be able to receive the X-band waves that are illuminating the target, even if the X-band radar itself is not receiving them. That's why another name for these extreme examples of the bi-static concept is "blind illumination". The (X-band) radar itself  is "blind". It is not receiving any return from the stealth aircraft which is say, 120 km away. But the missile and crucially, its radar receiver, is only 5 km away. It is close enough to receive the X-band radar waves being reflected back from the target. The rest is simple - with an X-band return, the missile is able to close down the target and destroy it accurately. That's how the bi-static effect can be exploited to destroy stealth targets.

This diagram depicts bi-static radar operation, with the closest radar representing the missile's radar receiver

Conclusion

Bavar-373 is an advanced anti-aircraft system. Iranian engineers appear to have made efforts to give it an anti-stealth capability. The system emulates the S-300 in how it is laid out and its mode of operation, but with key differences to suit Iranian needs. And on a subsystem level, it is completely indigenous. This will allow Iran to easily upgrade Bavar and integrate it into its air defence network. The next step for this system is active deployment.

Specifications

Maximum detection range: 320 km
Maximum tracking range: 260 km
Maximum engagement range: 200 km
Maximum engagement altitude: 27 km
Simultaneously detected targets: 300
Simultaneously tracked targets: 60
Simultaneously engaged targets: 6
Simultaneously guided missiles: 12
Maximum missiles per battery: 24

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