PLAN Type 052C/052D Class Destroyers

Discussion in 'Navy' started by Jeff Head, Mar 14, 2014.

  1. Tam
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    Tam Senior Member
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    Was writing it so fast while sleeping in my bed, so I didn't compose this properly. Range determines the total signal time, since the receiver has to wait for the echo to be received before the transmitter can send out again. Duty cycle is determined by pulse width / signal time. You can have an extremely short pulse width characterized by high peak power, or a longer pulse width with lower peak power, but the PRF would remain the same no less and so will the total energy being transmitted. What would change is the PRR or the length of time of Receive, before Send again. So the number of pulses sent out per second will be the same, based on range, with 300km per millisecond which is the speed of light. So the total travel distance is going to the target, then reflect back to the source, the range would be half that. Total signal time itself is a reciprocal of PRF. But there is also a dead time where phase shifters have to be reset, and that is done during this waiting period.
     
  2. Tam
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    Tam Senior Member
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    Posted by LKJ86 at the PDF. Would be interesting to read what is on the magazine.

    img-65f27e050e434324b99f9920b5bde771.jpg
     
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  3. Max Demian
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    Max Demian Junior Member
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    @Tam

    Another definition of duty cycle that I often come across is the percentage of time the radar is radiating. Many articles multiply that number with peak power to derive average radar power.
     
  4. Max Demian
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    Max Demian Junior Member
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    From this article:

    "The proposed APAR, contains 3584 TR modules per aperture, so each module must consume less than 1.5W. In order to achieve this goal, peak transmit power is limited to 4W at 10% duty cycle rather than the 8W the PA is capable of delivering. In addition, the LNA duty cycle is limited to 90%. This results in a total power dissipation of approximately 1.5W"

    I am reading this: for 0.4W (10% * 4w) radiative power, 1.5W is dissipated.
     
  5. Tam
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    Tam Senior Member
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    Duty Cycle is Pulse Width / Pulse Time. Pulse Time, which is the time one pulse starts to the time the next pulse starts, is determined by range. You have to remember that Pulse Time is greater than Pulse Width, as it also includes the time the radar is receiving, or the Receive Time, and the total pulse time must allow enough time for the echo to return. Shortening pulse width does not decrease pulse time, nor does it increase pulse repetition frequency as some of your links you brought up seems to imply. A high PRF is needed to fast track a target.
     
  6. Max Demian
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    Max Demian Junior Member
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    I am curious, how do you express the PRF of a multi-beam AESAs?

    More to the topic, it seems to me that 25W peak power per S-band TR element on Type 346 seems consistent with mid 2000s state-of-art, where 10W peak power for X-band was the high-end. Although, per Wiki article, they had to combine 4 T/R with one 100W amplifier due to limitations in fabrication capability.

    Assuming 5000 TR elements, we get 125kW peak power. Average power would certainly have a cooling ceiling. Given some of the sources I linked, the dissipated power is anywhere from 122% to 375% that of radiated power. This ppt states a PAE of 25%, in line with the figure from the APAR weather radar article I linked (where the total system input/output efficiency was close to 20%).

    Comparison to a high-power AESA. The AN/TPY-2 has an average power of 81kW (peak 405kW) on a 9.2m2 array for heat intensity of 26.4kW/m2 (30% efficiency). It is liquid cooled. The Type 346 is only air-cooled. This thread has some numbers for air-cooled vs liquid-cooled AESAs: http://www.f-16.net/forum/viewtopic.php?f=38&t=53650

    There is a rough number of 2kW/m2 for air-cooling (quoted from Radar Analysis and Modeling" 2005 edition by David K Barton). Caveat: attainable numbers are system design dependent.

    Assuming an area of 13.8m2 and 2kW/m2 dissipation gives us about 27.5kW average dissipated power per radar face for Type 346. Note: I computed the area by linearly scaling the SPY-1 4350 element array of area 12m2 to a 5000 element array. Assuming 20% system efficiency (generation gap) would give us an average power of about 5kW per radar face. Needless to say, this would be a pretty bad result. Should double-check the equation from that book. I am curious if that is for forced air cooling or not.
     
    #3116 Max Demian, Mar 15, 2019
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  7. davidau
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    davidau Junior Member
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    ...what a difference a couple of decade make..the old & the new DDG 150 Changchun ...

    ...the new .. blue waters navy .. including ship protection, escort duties, good-will visits in foreign ports, in the gulf ...
    [​IMG]

    [​IMG]

    [​IMG]

    and...the old.. green waters navy..in
    [​IMG]
     
    #3117 davidau, Mar 15, 2019
    Last edited: Mar 15, 2019
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  8. Tam
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    Tam Senior Member
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    PRF is independent of array type. Regardless whether is mechanical parabolic or AESA, PRF is PRF and is a function of range. The closer the target is, the higher the PRF, the farther the object is, the lower the PRF is required.

    100W amp S-band modules are not uncommon today. Wiki article feels like the author makes it sound like a pain in making one.

    Here is one being sold right now, and just so happens to be also a QTRM.

    https://www.apitech.com/products/rf...esa/s-band-quad-transmit-recieve-module-qtrm/

    And another one.

    https://www.rfglobalnet.com/doc/s-band-and-x-band-transmitreceive-modules-0001

    Why don't you account for density? Why you keep comparing X-band to S-band? Element per meter square is much lower on the S-band than an X-band. AN/TPY-2 has over 25,000 elements over a 9.8m2 vs. over 5,000 S-band elements over a 13.3m2 area for the Type 346. One needs to account for the total surface area of each module in all three dimensions, length, width, and height. As for air cooling, the prototype for the radar on the weapons test ship is spotted with huge large pipes around the radar. Those pictures are hard to find now due to their age but I still remember them. My immediate thought about those pipes is that they resemble those of a large refrigeration system, and outright betray the array as an AESA. The presence of large pipes does not make it clear if it is liquid cooling or forced air that itself is cooled to a very low temperature. There is no way of knowing the volume and transfer rates of the air if it is air, nor the temperature of the air as it is cooled.

    You also need to account for the design of each plank and array units, how each array unit and plank conducts heat, the design and packaging of each module and how each module transfers heat away. Given the larger size of an S-band element, there is more surface area for the module to dissipate heat. Packaging and heat transfer is extremely important for any AESA element. However, knowledge of the packaging and heat transfer methods are highly proprietary and classified.

    https://www.apitech.com/globalasset...utions/imas--subsystems/aesa/aesa-trifold.pdf
     
    #3118 Tam, Mar 15, 2019
    Last edited: Mar 15, 2019
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  9. Max Demian
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    Max Demian Junior Member
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    That's because the story takes place in the early to mid 2000s, more than 10 years ago. Also, I don't think quad packed TRs were top tier products even back then.

    What I was trying to establish is an upper bound for transmitted RF power on the assumption the radar is air cooled. Using the total antenna surface is not unreasonable, given that the panel also serves to transmit the heatload to a heatsink. Obviously, there will be hotspots around the power amps of TR elements and any real cooling solution needs to ensure that those don't exceed design thresholds. However, given that we know next to nothing on the actual panel composition we cannot even start making a model for that.

    Therefore, a comparative study. I picked the AN/TPY-2 not because it's X-band, but because it's a high power AESA radar whose many operational parameters are publicly available. If you happen to have similar data on a S-band AESA, that would be even better. Perhaps we can apply a multiplicative factor to account for the fact that cooling an S-band is likely easier than X-band due to lower power density.
     
  10. Max Demian
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    Max Demian Junior Member
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    Continuing post #3119

    I decided to directly apply the pasted formula from the book Radar Systems and Analysis. This formula takes into account the module cross-section as function of lambda.
    I used the following parameters for Type 346:
    N_e = 5000
    H_d = 2kW/m2 (max allowed heat density using air cooling at sea level)
    eta = 0.2 (efficiency)
    lambda = 0.09m (roughly corresponding to 3.3GHz)

    The calculated max allowed average power comes out to roughly 10 kW per radar face. This will linearly scale with the number of elements and quadratically with the wavelength.
     
    #3120 Max Demian, Mar 16, 2019
    Last edited: Mar 16, 2019
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