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Monday, November 13, 2023

Radar – Rotating vs. Panels

We previously compared vertical launch systems (VLS) to arm launchers (see, “VLS Versus Arm Launchers”) and concluded that VLS was not quite the unquestioned advantage that it was claimed and assumed to be.  Similarly, we’re now going to compare rotating radars against fixed, flat panel arrays which are assumed to be infinitely superior.
 
One of the major developments in naval sensors has been the advent of flat panel radar arrays.  The panels are mounted on the sides of the superstructure with, typically, 3-4 spaced around so as to provide 360 degree coverage, each panel covering 90-120 degrees.  This architecture is assumed to be hugely more beneficial than conventional, rotating radars, presumably due to the elimination of moving parts as well as the simultaneous improvement in radar technology, generally.  Is this assumption of superiority valid?  Let’s see.
 
Let’s start by understanding the three basic types of radar configurations:
 
Conventional Lattice – These are typified by the SPS-48/49 which are modern versions of the classic, mechanically steered, rotating radars with a lattice framework.
 
Wasp class with SPS-48 on the right and SPS-49 on the left


Hybrid Panel – These place flat panels on a rotating assembly to produce a hybrid rotating panel.  Examples include the TRS-3D which rotates at 10, 17, 20 or 60 revolutions per minute (rpm) [1] or the TRS-4D which rotates at 15, 30 rpm [2].  Both are quite capable.
 
TRS-4D is a G-Band three-dimensional, multi-function naval radar for surveillance, target acquisition, self-defense, gunfire support, and aircraft control. It is a software-defined radar using a rotating version of the active electronically scanned array (AESA) with multiple digitally formed beams. …
 
The TRS-4D radar simultaneously conducts a three dimensional search of the air space volume and sea surface area around the ship. … The transmitter modules in the active antenna are solid-state modules in Gallium Nitride technology. The radar allows a graceful degradation of the transmitted power depending on the required maximum range.
 
The MRESR version of the TRS-4D was installed on US LCS ships of the U.S. Navy’s Freedom class. It was designated by US Navy as AN/SPS-80.[2]


TRS-3D

 
Another example of a hybrid panel radar is the SPY-6(V)2 which is intended to be installed on amphibious ships and Nimitz class carriers.
 
SPY-6(v)2


Panel – These are the ubiquitous flat panels found on US ships and include the various Aegis SPY-1 variants, SPY-6 (Air and Missile Defense Radar, AMDR), SPY-6(V)3 Enterprise Air Surveillance Radar (EASR), and whatever other names they’re known by.
 
Flat Panel


Advantages and Disadvantages
 
Simplicity.  Flat panels are mechanically simpler in that they have fewer moving parts although, to be fair, a motor and some bearings to rotate on are not exactly rocket science in terms of complexity.  Still, no movement is undeniably simpler than rotating.
 
Of course, rotation is not the end of the simplicity story. 
 
Both types require sophisticated, complex computers/software to control and process the signals so that’s a wash.
 
What isn’t a wash is the extent of electronic and utility support that a panel requires.  Each element in a panel requires its own power, computer connections, data and computer control connections, and cooling support.  A rotating radar requires much the same but only a single instance of each, as opposed to an instance for each element of the array.  Notably, rotating radars do not require cooling which is a major requirement.
 
Further, the individual modules that make up a panel are quite complicated and there is no hope of repairing one aboard ship.  On the plus side, they can be swapped out without too much difficulty, as I understand it.  Similarly, the ‘guts’ of a hybrid panel are similarly complex.  The conventional lattice is, of course, as simple as it gets.
 
Volume.  Rotating radars are essentially external to the ship whereas panels require significant amounts of internal ship’s volume to house the array elements and support equipment.  Further, panels typically exist as 3-4 repeated installations, each of which requires its own, equal, large amount of ship’s volume to house it.  Thus, rotating units require only, perhaps, a tenth of panel’s volume.  This is a significant consideration in ship cost and design.
 
Weight.  I do not have data on unit weights but I assume that panels, with 3-4 duplicates and large elements, have significantly higher total weight than rotating units.
 
Damage Resiliency.  Older, lattice type rotating radars have a degree of inherent damage resiliency in that their lattice structure is mostly space.  Shrapnel sprayed in their direction will largely pass through with little resulting damage.  The denser the lattice or, in the case of rotating panels, the greater the degree of damage susceptibility.  Rotating panels, while solid as opposed to a lattice, are smaller than a rotating lattice and significantly smaller than flat panels.  Thus, their size confers a degree of damage resilience.
 
Fixed panels, on the other hand, are absolutely certain to sustain damage from shrapnel.  One hundred percent of shrapnel from nearby explosions will impact the panel with every piece producing damage.  Manufacturer’s claim that panels are resistant to damage because the undamaged elements can continue to function, albeit at a lower overall efficiency and effectiveness.  However, this claim is unproven by any realistic testing.  For example, while a single damaged element may not significantly impact the overall radar performance, what is ignored is the cabling, communications, cooling, and power ‘behind’ the elements and those are extremely vulnerable to damage and would, when damaged, likely affect large portions, or all, of the panel.  The manufacturer’s claims do not consider this type of damage, at all.
 
When damage does occur, if you lose a panel, you lose that coverage sector (90-120 degrees) permanently.  There is no alternative mechanism to compensate.  You have a permanent hole in your coverage.  Not good in combat!  In contrast, a rotating radar provides full coverage until it is completely incapacitated.  In addition, the typical radar arrangement of -48 and -49 allows either radar to take over the other’s coverage in the event of damage.
 
Coverage.  Rotating radars, by their nature, provide only intermittent coverage as the active (transmitting and receiving) portion of the radar is always moving.  In many cases, such as tracking at long ranges, this is an insignificant issue since the target is not changing location fast enough to matter.  At closer ranges and higher target speeds, such as supersonic missiles inside the horizon, this can be a significant problem.
 
The problem of intermittent coverage can be mitigated by using higher rotational speed or using double sided radars which have active portions front and back thus providing near 360 degree coverage.
 
Alignment.  While I can’t speak to every panel radar that exists, the Aegis SPY variants apparently require a very precise alignment as evidenced by the impaired performance and required repairs of radars of ships that have grounded or been in a collision.  Whether this alignment sensitivity is true of modern panels, I have no idea.
 
Protection.  Flat panels are likely easier to protect with armor.  A simple armored cover can slide over the panel, as needed.  Rotating radars would require either a rotating, box-like arrangement or a retractable mechanism – doable, of course, but a bit more complicated.
 
Performance.  How effective is each radar type?  Panels and hybrids both use the same general technology so, ignoring size, there is no difference.  Of course, size does affect performance under certain circumstances (long range detection of small or stealthy targets, for example) and, in those cases, large panels would be preferred.
 
Detection range (against some theoretical target), alone, is not the measure of performance.  Performance is dependent on the circumstances of use.  If one is attempting to detect very long range, small targets, one would want the largest, most powerful panel possible.  Alternatively, if one is attempting to conduct a horizon range anti-air engagement, large panels are a waste and a small, rotating or hybrid radar would be preferred.
 
However, performance cannot be divorced from other aspects such as survivability, maintainability, repairability, size, weight, etc.  Performance must be appropriately weighted in balance with the other factors.
 
Bear in mind that manufacturers focus on extreme detection range against ideal targets as the measure of performance.  In reality, that is an unlikely use case in combat (EMCON being the default state!) where horizon range engagements are the far more likely scenario.  Being able to detect a stealth mosquito a continent away is of no use when engaging missiles from the horizon in.
 
The interesting aspect of performance is the question, to what degree can a conventional lattice radar be improved?  There seems to be no end to the degree of improvement that panels can undergo but what about lattice radars?  Can they be improved?  How much?
 
A closely related question is, to what degree do lattice radars need to be improved.  Given that we’ve stated that horizon range engagements are the most likely use case, and knowing that lattice radars have theoretical detection ranges of hundreds of miles (against suitable, theoretical targets), how much better do they need to be?  Perhaps they’re more than sufficient, right now?  If a lattice radar can provide, say, 90% of the required performance at a miniscule fraction of the cost, is that not good enough?  I can’t answer that.  I merely pose the questions but they are important questions.
 
 
Conclusion
 
It is clear that each type of radar configuration has advantages and disadvantages and that modern flat panels are not the unquestioned superior choice that most assume.  The choice of radar configuration depends on the balance between all the factors.  It would seem that hybrid rotating panels represent the best balance, overall.  They have good performance, less weight, consume little internal volume, provide adequate coverage, and have a reasonable cost.  Of course, much depends on the use case.  For example, a dedicated AAW ship might well justify multiple, large panels.
 
For general purpose surface ships, a hybrid rotating panel is the best choice.
 
 
 
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23 comments:

  1. I'd like to say, that while most SPY users use the large panels used on the american ships, there is a growing number of foreign systems that use a number of smaller panels with different wavelenghts that are installed higher up in the enclosed mast offering very interesting capabilities.
    Many of the same companies offer the same radar used in a flat panel installation as a rotating system using 1 or 2 of the same panels.
    In the end it's to the customer.

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  2. Does the cooling requirement go away because the rotating panel is completely surrounded by air and moving? That seemed surprising to me. Much easier to see that a lattice requires no cooling.

    How far the lattice can go is definitely one to ponder.

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    1. The cooling requirements decrease only in part with a rotating radar, as many systems are still installed in the hull and need to be cooled. I've been told that rotating radars can have problems with freezing in case of very low temperatures and very strong winds. Apparently fixed radars are less exposed to these problems.

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  3. Can the signals from multiple radars be amalgamated into a single usable format?

    For example, if you utilized a pair of double-sided, flat-panel, rotational radars and aligned them so they all point in four different directions....would the software be able to combine those signals into coherent, usable information?

    Lutefisk

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    Replies
    1. If they're rotating then they point in all directions! I'm missing what you're asking.

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    2. Sorry, I don't know much about radar.

      Are the four panels all amalgamated into a single readout.
      So the two twin radars would both feed into one comprehensive single display?

      And if one was knocked out, then the other three would still feed their info into one source for the crew?

      Did that make sense?

      Lutefisk

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    3. You're losing me!

      Yes, the multiple fixed panels feed into a single 'picture', so to speak. If one panel were destroyed, the picture would show only 3/4 of the surrounding area. One sector (a quarter of the area) would be blank.

      Rotating radars show 360 degrees for as long as they're operating. It doesn't matter how many you have or where they're located (unless they're masked by superstructure but no one would do that). It is possible to have multiple rotating radars feed a single picture. To the best of my knowledge, no one has built a ship with multiple main rotating radars yet although that would be a significant improvement in combat resiliency.

      Did that answer your question?

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    4. If you have 4 fixed arrays cutting to 3 won't lose you a whole 25% of your coverage, especially the further out you go. They over lap. Same with 3 face, you don't lose 1/3 if one is knocked out.

      Now a 2 face rotating radar like SPQ-9B has 2 small gaps in 360 degree coverage for a brief moment, shortened by the fact it rotates. My thought is, who wants to go up there and fix it if it breaks? Enclosed masts have ore than one handy use.

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    5. "Did that answer your question?"

      Yes, thank you.

      Lutefisk

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    6. I've been busy so I haven't had a chance to explain my thinking, but here is why I asked...

      My original thoughts for combat ships was to put flat panels oriented in the cardinal directions. A larger ship could have a second set of flat panels oriented in the semi-cardinal directions.
      This would give 360 degree coverage with redundancy.

      But you could achieve something similar, possible even better, by having a pair of two-sided rotating fixed panels.

      The advantage would be weight and cost savings by using half the panels, and no major loss in a particular azimuth with the damage or malfunction of a single panel.

      The disadvantage is that the rotating panels would be more difficult to armor.
      Probably the best way to do that would be to have an armored cylinder that the rotating panels could be lowered into quickly, kind of like hunkering down into a foxhole.

      I like this idea, what might be some pitfalls?

      Lutefisk

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  4. I've read that the British Type 45 destroyer, with rotating AESA radar at the top of a tall mast, can see significantly farther over the horizon than flat panel Burkes can, providing earlier detection and engagement of sea skimming missiles. Something the British specifically designed for after their experience in the Falklands. I just can't find that reference at the moment...

    Interestingly, the Type 45 also has a separate rotating version of the Thales SMART-L (conventional?) air search radar, something Burkes seem to lack. Is there some kind of weakness in the hybrid rotating radar (compared to the flat panel Aegis system) that this is compensating for? Or perhaps they serve different purposes?

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    Replies
    1. The Sampson radar, the ball on the top of the mast,
      is the fire control radar for PAAMS, inside therotating ball is a 2 face AESA radar, the SMART-L is volume search radar, 1 face rotating AESA.

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    2. There's a thorough description of the Sampson radar here.
      https://www.navylookout.com/in-focus-the-royal-navys-sampson-radar/

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  5. Id add one small note- the rotating antennas have to be "fed" the signal, and its not by wiring, but a waveguide (picture a metal tube roughly like a house gutter) that runs from the radar set all the way up to the antenna. On newer unarmored ships, they're easilly a failure point in battle due to even light damage, as a bit of bending, let alone shrapnel holes, will degrade or eliminate their usability. Still not as fragile as external flat panels, but somthing to consider, and shows the value of older concepts like armored conning towers, armored cable runs, etc...

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    Replies
    1. Note: that comment was specifically aimed at the older systems like the -49, -67, etc...

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  6. In general, we have to be careful in comparing the performance aspects, because there are incredible performance improvements in the newer generations that of course drive many of the tradeoffs described elsewhere. Setting those aside to just get at "rotating" vs "fixed face" the best one to compare is the SPY-6(V)2 rotating array shown above. It does most of the fun things the fixed face arrays do but in a rotating form factor - and I think it speaks to your point that Navy chose it for some ships over the fixed face arrays, but it does not conform to many of the pluses of rotating radars that you identify.
    - it is not a lattice, and I think you're underestimating the ability of the -48 and -49 to absorb damage and still function.
    - it does not have "a single instance" of the support components but has just as many as the fixed face ones do.
    - it's incredibly heavy (though not as much as 4 fixed faces, to be sure), as what we are asking modern radars to do simply cannot be done by the -48 and -49 style devices.

    Your ultimate point is valid that each ship's mission and needs should determine its provided radar, however unlike the VLS analysis I don't think this conclusion derives from the supporting arguments.

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    1. "what we are asking modern radars to do simply cannot be done by the -48 and -49 style devices."

      Why not? What are we asking that cannot be done? This is a genuine question which I alluded to in the post when I asked what level of performance we actually need? The glaringly obvious need is for horizon and in engagements and I see no reason why a -48/-49 can't do handle that perfectly well but maybe I'm missing something? What's your thinking?

      " it does not have "a single instance" of the support components but has just as many as the fixed face ones do."

      No. The flat panel SPY-6(V)1 has 37 RMA modules in each of four panels. The rotating SPY-6(V)2 has 9 modules in a single unit. Thus, the (V)1 has roughly four times as many "instances" of support components as the (V)2 and then it's four times that for each of the four panels that make up a single system.

      " it's incredibly heavy (though not as much as 4 fixed faces, to be sure)"

      The (V)2 is one quarter the size of the (V)1 so, roughly, it would be one quarter the weight of a single panel and 1/16th the weight of a complete (V)1 system. I suspect that the weight differential is even greater than that due to the much higher amounts of supporting cabling, cooling, etc. but I have no actual weight data so that's pure speculation on my part. So, not nearly as heavy as the (V)1 system which, to be fair, you acknowledge, if in a somewhat understated fashion!

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    2. "I don't think this conclusion derives from the supporting arguments."

      Actually, the Navy seems to pretty much agree with me. I concluded,

      "For general purpose surface ships, a hybrid rotating panel is the best choice."

      The Navy's plan/practice is for Burkes (dedicated AAW ships) and Ford carriers to have fixed panels while all other ships (LCS, amphibs, and Nimitz carriers) will have some form of rotating panel. The interesting case is the Constellation which is planned to have a miniature fixed panel (V)3, 9-RMA version which follows as the Navy considers the Constellation to be mini-Burkes.

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  7. I wonder how the combination of APAR/EMPAR/SAMPSON multi-function electronically scanned arrays with SMART-L/S-1850 rotating long-range radar, which seem to be preferred by various European navies, compare.

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  8. Unlike rotating radars, flat panel arrays, like the SPY series, can also be used to conduct EW attacks against ships, aircraft, and missiles. In addition, flat panel arrays make sea-based ballistic missile defense possible and can transmit updates to SAMs in flight.

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  9. When discussing radar still think the NATO Anti-Air Warfare System (NAAWS) study, which was completed in 1991 should be the start point, it recommended X and L band radars.

    The conclusion was its best not to mix surveillance and fire control and recommended X-band MFR for ship defense to deal with saturation attacks or multiple attacks and L-band VSR for long range search as it provides the optimal combination of complementary capabilities. X band 9-10 GHz, corresponding to a wavelength of about 3 cm which is about a factor of three shorter than that S band 2-4 GHz of about 10 cm, as the antenna gain is inversely proportional to the square of the radar wavelength giving X-band advantage by nearly a factor of ten in discrimination. The higher frequency you go the better performance you get against low altitude targets, X-band also has very favorable low-altitude propagation characteristics in that it adheres to the surface to extend its range beyond the horizon whereas lower wavebands do the opposite, that makes X-band very attractive for use in horizon search against low-flying ASCMs. In terms of low altitude propagation effect factor X-Band has 35 dB advantage over L-Band and 17 dB advantage over S-Band at a radar horizon of 21 kms when all these different band radars are positioned at a height of 26 m (Johns Hopkins).

    Lower frequencies as L-band, lack the X-band sharpness but are capable of covering much larger areas at lower power than X-band equivalent and substantially less cost, incur less signal attenuation (loss in power), regardless of weather and makes them suitable for tracking the position of a threat object at long ranges. S-band and C band are a sort of 'middle' frequencies and provide a balance between discrimination and tracking capability.

    On the question of rotating vs three or four fixed face radars, the argument goes a rotating radar when it is not looking at the target, it is predicting where that target is going to be for the next rotation and when faced with multiple threats from 360° degrees and if the threats are high Mach number and are maneuvering, it may not be where radar thought it would be and if it is not, you just lost the track history, you will see it again but it will take more than several rotations to pick it out and confirm it as a brand new threat and you are going to have start the kill chain process all over again losing precious seconds.
    PS the new Air Force/Lockheed L-band TPY-4 radar is a single face rotating at 6 rpm with a range of 300 nm, in starring mode the range nearly doubles to 540 nm, showing one advantage of more costly multi-face radars which allow a longer dwell time. Navy have stated that radar sensitivity scales as a cube of the size of the radar aperture.

    The Navy chose S-band for the SPY-1, SPY-4 and SPY-6 in preference to the previous generation L-band SPS-49 for its long range volume search radars, have never seen the rationale for the change.

    Navy did not develop the X-band AMDR radar as was in the original plan to save costs, just the S-band SPY-6, but Navy said it would use the old gen AN/SPQ-9B on the first 12 Burke Flight IIIs to be replaced by a new gen AMDR X-band radar in set 13, to date no sign of Navy is funding a new gen X-band radar for Burkes.

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  10. Hey Conops,
    Thanks for your writing.
    OT, but nonetheless ATM we have 2 CSGs in Middle Eastern waters, and maybe another 2 on the way.
    As well we have an Ohio-LAM carrier, an amphibious assault ship, THAADs, Patriot batteries, A10s, F35s, and the 101st Airborne on standby.
    Interested in your take on all this….

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  11. Hello ComNavOps. Interesting post as always.

    I re-read the VLS article and then followed the links onto your 2020 post about Virginia Class Cruisers. There was a comment which stood out:

    "Nuclear Strike Group. With the planned 11 ships of the class plus the two California class cruisers and the Truxtun, the Navy was on its way to assembling entire nuclear powered carrier strike groups. This would have OFFERED SOME SIGNIFICANT OPERATIONAL AND TACTICAL ADVANTAGES. The group would have required no refueling support and could have operated at high speed for extended periods thereby allowing for rapid repositioning. A highly mobile and self-sufficient task force would have been a significant benefit."

    Contrast with your recent 'Worst Developments Ever' post:

    "Surface Ship Nuclear Power – OFFERS NO OVERALL TACTICAL OR OPERATIONAL BENEFITS".

    Can I ask what has changed your mind on nuclear power?

    (apologies for the full caps. i couldn't figure out how to do bold text)

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