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Thread: AESA Radar range calculator.

  1. #1
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    AESA Radar range calculator.

    Greetings. It's been a while since i post a thing here.. bit boggled with some IRL issues. But well here i come.

    So what i shared is, kinda small project of mine based on my interest toward radar.

    The AESA Radar range calculator here is an excel spreadsheet, made based on several books like SKolnik's 3rd Introduction to Radar system, Stimson's 2nd Edition of Introduction Airborne Radar and others.

    The calculator will attempt to predict radar ranges based on inputted variables and taking account of some important things that for some reason not considered by other calculators like pulse integration, scan sectors and most importantly the antenna weighting scheme.

    As we know AESA Radar or perhaps even its Hybrid Array sibling like N011M Bars is capable of actually altering its radiation pattern, based on algorithms like Taylor, Cos, Hamming. etc. Even special algorithm has been developed for AESA. The change in radiation pattern allows reduction in sidelobe, beamwidth optimizations, or even total split of the aperture into several smaller one for search. In cost of efficiency and angular resolution.

    This calculator however are still what you call as "Noise limited", basically it's not taking account things like ground clutter or weather. However i think for case like high altitude combat, it's good.

    It has simple interface and i believe quite easy to understand.

    Click image for larger version. 

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    The download link.

    http://www.mediafire.com/file/7wrkys...CalcTrial.xlsx

    critics and suggestion are welcome.

  2. #2
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    Very detail , i love it.

  3. #3
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    Great work.. congrats.. far more advanced and detailed that I could ever have gathered together..

    one thing if I might ask.. is it possible to upgrade a radar with an antenna of a certain aperture and certain amount of elements by replacing the antenna with a different one with larger TRM count? Say your APG-77 has 2,000 TRMs, today, could it get a 2,700-TRM array one day? I am quite sure that the R&D and technology enable to pack the TRMs into tighter space, but ain't the physical dimensions of the emitter/receiver limited/dictated by the respective radar band?

    thanks

  4. #4
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    AFAIK, Too narrow spacing between T/R modules may cause the system to have bad overheat or mutual coupling

  5. #5
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    Looks great.

    What are the parameters which control beamwidth? I always taught about a AESA that concentrates the RF energy via resonance and hence achieves greater ranges. At some point the amount of airspace electronically scanned would increase the time for a complete scan of the hemisphere too much. But for specialized purposes such as target illumination, could the beamwidth be significantly improved compared to a PESA?

    Thanks.

  6. #6
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    Quote Originally Posted by PeeD View Post
    Looks great.

    What are the parameters which control beamwidth? I always taught about a AESA that concentrates the RF energy via resonance and hence achieves greater ranges. At some point the amount of airspace electronically scanned would increase the time for a complete scan of the hemisphere too much. But for specialized purposes such as target illumination, could the beamwidth be significantly improved compared to a PESA?

    Thanks.
    The beamwidth of the AESA is directly controlled by the number of its elements, which govern the physical dimension of the antenna. Weighting algorithm can later be introduced to control radiation pattern. However one cannot really make beam narrower unless the antenna is enlarged.

    In the calculator the basic equation to calculate beamwidth is :

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    The resulting beamwidth is later multiplied by the "Beamwidth factor" or "K" from the tapering algorithm drop down menu.

    Quote Originally Posted by MSphere View Post
    Great work.. congrats.. far more advanced and detailed that I could ever have gathered together.

    one thing if I might ask.. is it possible to upgrade a radar with an antenna of a certain aperture and certain amount of elements by replacing the antenna with a different one with larger TRM count? Say your APG-77 has 2,000 TRMs, today, could it get a 2,700-TRM array one day? I am quite sure that the R&D and technology enable to pack the TRMs into tighter space, but ain't the physical dimensions of the emitter/receiver limited/dictated by the respective radar band?

    thanks
    Apparently that's the plan for US AMDR Radar, where they have some sort of "common module" block. So what you need to "upgrade" is Physical space. For fighter radar tho, i am not so sure as the space and power generation there is very premium.

    There is of course another consideration of using less modules than what an antenna can actually accommodate like cost or RCS reduction, from edge treatment. Other possible consideration is cost as we know TR module is still an expensive item. Cost issue become critical if you desire to use higher frequency (say 94 Ghz AESA) and wish for a full array. you would need thousands of modules.

    Anyway related to cost, i included a small chart depicting several factor and their relations to wavelength. As you see cost increase exponentially when you move to higher frequency (shorter wavelength)

    The size of the AESA T-R module is governed by physics. The width is the primary dimension, where it need to be about half wavelength. So for X-band the module's width would be about 1.5 cm for 3 cm operational wavelength. Technology can only goes as far as packaging, cooling and materials.


    Quote Originally Posted by garryA View Post
    Very detail , i love it.
    Thanks a lot.
    Attached Images Attached Images  
    Last edited by stealthflanker; 20th March 2017 at 22:16.

  7. #7
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    Updates

    Slight updates to the calculator. The Required SNR variable is now automatically calculated by the spreadsheet.

    The Calculated SNR is for Swerling 1 or 2 target. Representative for maneuvering fighter aircraft, and basically the goal of any fighter/tracking radar designer (as making the target behaves in swerling 2 will reduce the required SNR)

    As you see no more SNR variable.
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    Instead it's become part of the calculated variable. The calculated SNR is for 90% probability of target detection. Which allows lock on. Thus the R90 in the bold coloumn is the range where target could be locked on by the radar and later fired upon by the radar platform.

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    The range coloumn
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    The R50% is the range where target detection probability is 50%. Such range is where radar might detect and track the target But not having the confidence of locking it for weapon system employment. It may however be used to cue other fighter aircraft or higher resolution sensors to establish more confidence on what being detected, is it real target or just false alarm.

  8. #8
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    So many variables iam overwhelmed with choices.

  9. #9
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    what do you mean @moonlight ?

  10. #10
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    for laymen it would be easier if there were just several choices, and everything else was approximated (average and/or generic values used), even if it meant significantly greater errors.

    Anything other than these variable might confuse most people: output power, antenna diameter, target RCS, wavelength.

  11. #11
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    @totoro Thanks for the input.

    Let's see what i could do. Using approximations is good however the calculators may lost its flexibility. and some variables like PRF can't really be "automated" unless locking the calculator in specific frequency (say X-band) But we will see.

  12. #12
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    Improvements time. Trimming down some variables and Provide pre-calculated one. The calculator basically remains the same BUT hopefully it's more user friendly.

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    The cover page now feature less clutters and lesser amount of input. Unfortunately as i said previously, pulsewidth and PRF cannot really be "automated" as it depends on the radar mode. Eliminating them will essentially locks the functionality of the calculator to X-band. While we know Russian developed L-band leading edge radar. and we have AEW AESA radar such as APY-9 and Elta Phalcon.

    For filling guide for PRF and pulsewidth however. One can consult to following table, genereously provided by Carlo Kopp in Radar Handbook 3rd Edition. For both A2A and A2G modes

    A2A


    A2G



    The second page of the calculator contains the pre calculated variables. One may still edit them. However it could be left as is. The pre calculated variables are based on generic information provided by radar literature in my possession.

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    Hopefully it could be more useful and easier to use. However feedback and input are appreciated.


    Download link for the Improved version :

    https://www.mediafire.com/file/7wrky...CalcTrial.xlsx

  13. #13
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    is it possible to upgrade a radar with an antenna of a certain aperture and certain amount of elements by replacing the antenna with a different one with larger TRM count?
    Unless the modules were larger than half wavelength for some weird reason, the answer is no.

    If you tried to space the modules closer than lambda/2, you'd end up with multiple beams going in different directions. Not very useful for a radar.

  14. #14
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    VERY complicated, but certainly not impossible AFAIK, changing time shifts no?

    lambda/2 is linked to 60° value isn't it?

  15. #15
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    If you tried to space the modules closer than lambda/2, you'd end up with multiple beams going in different directions. Not very useful for a radar
    AFAIK, lambda/2 rule is for upper limit rather than lower limit. Lambda/2 spacing give the best gain though IMHO

    Last edited by garryA; 2nd September 2017 at 09:53.

  16. #16
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    What gain ?

    Anyway Lambda/2 spacing from image above give scanning without grating lobes. Any other spacings be it less or more should have other consideration on choosing like say economy. The risk associated by using other form of spacing for ESA elements are limited steering angle. One example is ESA modules in TOR-M1 system which have wide spacing of lambda*3. The Russian designer opted such scheme for economy while providing best aperture area and gain possible. Whle accepting electronic steering angle of only 7 degrees.

    Other possible reason for choosing non half wavelength scheme is stealth as to reduce bragg lobes. Bragg lobes

  17. #17
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    @stealthflanker:
    I mean there are too variables so i don't know what to choose to calculate range. For example: I want to estimate air to air range of radars like APG-77 and APG-81. But i have no idea what to put in Doppler filter per band or system loss budget. Even pulse width is hard for me to decide, especially with technology like pulse compression. Basically what said by totoro.
    Last edited by moon_light; 2nd September 2017 at 14:29.

  18. #18
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    I want to estimate air to air range of radars like APG-77 and APG-81
    I gave it a shot:
    APG-81:
    T/R modules: 1626
    Peak power per module: 10W
    Operational wavelength: 3 cm
    Aperture weighting: Taylor40D
    Radar PRF: 10 Khz, Pulse width: 20 micro sec => Duty cycle: 20 %
    Scan time frame: 9 seconds for full search volume.
    Scan volume: 20° azimuth, 10° elevation (Cued search => longer dwell time => longer range)
    Against target with RCS = 3m2
    Maximum detection range with 50% probably of detection = 391 km
    Maximum detection range with 90% probably of detection = 242 km
    Last edited by mig-31bm; 5th September 2017 at 06:07.

  19. #19
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    When I reduce the radar scan sector angles I would expect a rather proportional increase of detection range, but sometimes there is even an decrease. Is the aperture gain included in the spreadsheet so that there is a limit from which on no increased detection range can be achieved by confining the scan angles?

  20. #20
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    The limit lies in the pulse integration loss. Not all of them can be integrated by the radar, and thus integration loss occurred. This in radar range equation will actually increase the required signal energy for target detection.

  21. #21
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    It is update time and various other stuff.

    What's new :
    -Antenna type added
    https://sta.sh/024qp486qzs7

    Allow range calculation for typical aircraft nose radar and linear array that might be embedded in your wing leading edge or vertical stabilizer.

    -Scan time now determined by dwell time.
    An advantages of AESA or general ESA radar is that the beam is controlled by computer and practically have no inertia, thus can be precisely controlled to achieve required dwell time/time on target.

    Dwell time is basically the time where radar beam will "stay" in a sector. It's a fraction of the total scan time (or time frame) or in fighter aircraft we know it as "scan cycle"

    This is typical fighter aircraft radar scan scheduling. As you see typical scan for fighter aircraft radar is about 1-5 seconds. Too long may cause problem in terms of update rate and tracking verification. In conventional mechanically scanned radar, this determined by the mechanical ability of the radar (actuator, hydraulics etc), which not much can be done with it.

    Click image for larger version. 

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    In previous version user can input their scan time, which later the sheet will "allocate" it according to the scan area inputted by user. In this new version the scan time is now dependent on dwell time, which now made select-able in drop down menu by user.

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    The value in the drop down menu is based on Typical dwell time for Long range early warning radar, target acquisition and typical fighter radar found in table 1.8. ch1 from Lynch's "Introduction to RF Stealth"

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    Another additional function is atmospheric effects in shape of attenuation by atmosphere, and rain.

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    I would like to add snow, but there seems to be problem in interpolating available data, or more like it's kinda hard to do so due to nature of atmospheric absorption. However for typical radar frequency it appears to be quite satisfactory. The model used is based on simplified K.Barton's atmospheric attenuation model. There is more complete model by L.V Blake, but i decided not to use it for now to keep things simple.


    Another improvements and additions are the antenna weighting algorithm. adding new algorithms which you can try and have fun with. If anyone asks why Taylor is the default it's because Taylor weighting is the easiest to implement and quite robust.

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    Below the weightings there are new tables detailing antenna parameters for Linear and planar array. They're there to help calculating range in the next worksheet. The assumption for the linear array however is as follows :
    1.Microstrip patch, with aggressive tapering in elevation beamwidth, original beamwidth was 114 degrees. However with proper lens treatment it can be reduced to the value you see in the table.
    2.The spacing would still be half wavelength thus entire array length would be N*d where d is spacing in half wavelength. and beamwidth is Ka*(2/N) where N is number of elements and Ka is the weighting factor.

    The planar array is your typical nose radar.

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    Below the antenna table lies the dwell time selection table. This table lies the dwell time and will calculate the required scanning time based on the number of beam positions need to be scanned. In case you see changing the value of the scanning area increase the radar range, it's because the sheet will adjust the value of the scanning time to the new sector. You can edit the dwell time value to your fitting. The scan time however is off limit.

    Major change in Pre-calculated worksheet. Now most of it are automated Thus can't be edited. You can still however edit the value on green columns

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    System temperature now fully automated.
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    Loss budget, some of it are still editable, and the radar range gate and receiver columns too.

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    The fluctuation loss modeling. Now it's fully modeled. The target is assumed to be Swerling case-2 target. Suitable model for tracking radar and what radar designer want target behave to. Swerling case 1 could also be applied. However this model is more suitable for search radar, esp rotating search radar.

    Click image for larger version. 

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    The new worksheet. The atmospheric effect, the most likely source of problem. This worksheet contain the "atmospheric model" and radar receiver noise figure "model" Based on excel trendline interpolation. The data is fortunately fits well so, the calculator is "work" However in the future i will implement better module.

    https://sta.sh/025kc3vsbsp8

    https://sta.sh/0sz0c9zanfw

    As always feedback are appreciated.







    Download Link for updated version :
    https://www.mediafire.com/file/7wrky...CalcTrial.xlsx

  22. #22
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    Just want to share bit of attempt in calculating "potential" range of L-band wing leading edge radar.

    Click image for larger version. 

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    The assumption is Very Long dwell strategy of 0.3 seconds per beam positions making total scan time of 250 seconds. Shorter dwells of 0.1, 0.025 and 0.01 seconds are shorter ranged BUT faster update rates. The range are 54-120 km for the target. Such long dwell time is possible, however i wonder if the update rate would be acceptable.

    The most difficult thing to predict is the change of target RCS. In this respect i rely on "Radar Cross Section 2nd Edition" Where it mention that object designed for low RCS in X-band will have 18dB more RCS in L-band (1250 MHz) Thus object having 0.001 sqm (-30 dB) RCS in X-band will have -12 dB or 0.06 sqm RCS in L-band.

  23. #23
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    @stealthflanker
    Just want to share bit of attempt in calculating "potential" range of L-band wing leading edge radar.
    You made a mistake, there are only 24 elements on 2 leading edge, 12 on each. So your T/R number is double.

  24. #24
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    The assumption is Very Long dwell strategy of 0.3 seconds per beam positions making total scan time of 250 seconds
    How wide is the beamwidth?. That sounds like either the beam very narrow or the search sector is very wide.

  25. #25
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    @moon_light

    They were operated as one radar. and see this :

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    Beamwidth for Horizontal is Narrow because of number of elements. Linear array beamwidth is basically 2/N Thus for array of 24 elements it is 2/24=0.08 Radian or 4.7 degrees. Vertical beamwidth would basically be the element's beamwidth which in this calculator assumed to be a patch with 114 degrees of vertical beamwidth. and no lens optimization. Beam positions need to be scanned is thereby low as the radar only scan in azimuth.

  26. #26
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    @stealthflanker
    Beamwidth for Horizontal is Narrow because of number of elements. Linear array beamwidth is basically 2/N Thus for array of 24 elements it is 2/24=0.08 Radian or 4.7 degrees. Vertical beamwidth would basically be the element's beamwidth which in this calculator assumed to be a patch with 114 degrees of vertical beamwidth. and no lens optimization. Beam positions need to be scanned is thereby low as the radar only scan in azimuth.
    Horizontal beam width of 4.7 degrees, if the search sector is 120 degrees then we have 25-26 beam positions. How did you get 250 seconds total scan time if dwell time is 0.3 seconds? I got approximately 7-8 seconds total scan time.
    With vertical beamwidth of 114 degrees, wouldn't radar range heavily reduced by clutter?
    Last edited by moon_light; 25th September 2017 at 10:33.

  27. #27
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    @moon_light

    You don't divide scan area with beamwidth. To get the scan time or "time frame" The methods is as follows :

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    Derived from original equations from Stimson's Introduction to Airborne Radar 2nd Edition

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    Well admittedly clutters is not in the calculator yet. However if i decide to include it you will have to input at least flight altitude and grazing angle to determine clutter patch area. Plus we may have types of clutter, is it surface (Ground patch) or volume clutter (chaff, clouds or flocks of birds) For sea clutter we may have sea states.

  28. #28
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    And now a quick fix for the Linear array. Since the Beam only scan in azimuth. The equation for scanning time/time frame must be adjusted that it no longer include the vertical scan for the radar.

    Download Link
    https://www.mediafire.com/file/7wrky...CalcTrial.xlsx

    -------------
    Furthermore regarding the addition of clutter and possible ECM. I would work on brand new calculator, and includes method to calculate SIR (Signal to Interference Ratio) and others like SCR (Signal to Clutter Ratio). The main problem with this is that there are no real closed form solution for calculating range. E.g the calculation would be done in iterative manner. The equation would include range as variable and the result would be Detectability factor (Dx) Which later be compared with required detectability factor.

  29. #29
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    You don't divide scan area with beamwidth
    But why not? what is the difference?. I still find it weird that you got 250 seconds.

  30. #30
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    Well have you looked at the equation i posted ? It's not simply like that. The beamwidth is squared.

    The mistake i did however is that i still included the vertical scan part which i fixed immediately. Now you got only 57 seconds instead of 5 minutes.

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