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IWR6843AOPEVM: Calculation of Radar Equation

user6843
Prodigy 170 points
Part Number: IWR6843AOPEVM

Hi,

I'm sorry for that very basic question, but I'm struggling with the radar equation. 

I used the equation from page 50 of this presentation and try to calculate it in Matlab (see attached pdf). But in comparison to the sensing estimator, I get a different solution (see attached picture) and I'm not sure we're my fault is. 

Furthermore, the sensing estimator shows the dependencies from the maximum range to the (range, velocity) resolution. This makes perfect sense in a logical way, but I'm not sure how these dependencies are linked to the radar equation.  

Regards,
Anne

radarEquationTI.pdf

  • +1
    TI__Mastermind 32905 points

    HI, there:

    The main issue I can see is the T_meas in your script.  The measurement time should only contain the ADC sample time, you need to exclude any idle time, ADC start time and excess time in the chirp and also you need to exclude any extra time in the frame that is not used for chirping.  

    I also notice that you have include 15dBm for transmit power, it is actually 15dBi, which includes the TX antenna gain. The reason we only include dBi for AOP datasheet is because AOP board do not have access point to measurement transmit power before antenna. Therefore, you should use 10dBm as TX power, and then program TX antenna gain as 5dB and RX gain as 5dB.   These should be done for both your MATLAB script and in the sensor estimator.  And this is not the part contribute to the mis-match, but more to make your analysis more realistic.   

    Best,

    Zigang

  • 0 in reply to zigang Yang
    Prodigy 170 points

    hey,
    thanks for the hint with T_meas, I'll correct that. 

    I'm not sure, if I'm getting your correction on the transmit power. That's what it says in the datasheet

    Do you want to express the following connection: EIRP[dBm] = P_t[dBm or dBi?] + G[dBi], with G=5dBi and P_t the transmit power. Did I understand that correctly? Your text is confusing, you say transmit power is 15dBi and than suggest to use 10dBm as transmit power. 

    Gain usually depends on the relative position from object to radar, so transmit power changes with the postion of the object relativ to the radar?
    And where do you get the 5dBi from? 

    Best Regards,
    Anne

  • 0 in reply to user6843
    TI__Mastermind 32905 points

    HI, Anne:

    Yes, you are right, I am trying to say EIPR includes transmit power and transmit antenna gain, total of 15dBm.  Sorry for the confusing.  The TX power is usually in dBm and antenna gain is in dBi.   AOP antenna gain is listed around 5.2dBi at: http://dev.ti.com/tirex/explore/node?node=AGMzFzzFdFllMlyaWeXNlw__VLyFKFf__LATEST 

    The one relative to the distance is the propagation loss, not the transmit antenna gain. 

    Best,

    Zigang

  • 0 in reply to zigang Yang
    Prodigy 170 points

    hey,

    thanks for starting another explanation! 

    To the "gain"-part of my question: I meant the angle, not the distance. Sorry for that. 

    I just checked the radiation pattern in the data sheet. It seems to me, that there's around 7 to 8 dBi at 0° and something less at for example 30°. So if "transmit power = EIRP - Gain", it would change with the angle or do I get something wrong? 
    Are 5dBi like an average over the beamwidth or where do they come from? 

    Best Regards,
    Anne

  • 0 in reply to user6843
    TI__Mastermind 32905 points

    HI, Anne:

    There is some system loss that was not incorporate in the antenna simulation result.   5.2dBi is the number I received from the our antenna designer.  It is the gain for the bore sight, not the average number over certain FOV.

    Best,

    Zigang

  • 0 in reply to zigang Yang
    Prodigy 170 points

    Thanks for your help!

    I still don't get the same value as in the estimator, but it's not that far away, so I think that's good enough for my pupose.

    Regards,
    Anne

  • 0 in reply to zigang Yang
    Prodigy 170 points

    Hi Zigang,
    I'm again confused by the properties of your antennas. I tried to sum the numbers up in the following table. I marked information green if they're clearly stated and red if I'm not sure about them. 

    My first question: Do the information in the toolbox (https://dev.ti.com/tirex/explore/node?node=AGMzFzzFdFllMlyaWeXNlw__VLyFKFf__LATEST) refer to the whole system or to one (transmit) antenna?


    Second question: Typically, the calculation for the EIRP includes some losses: EIRP = P_t + G + L, where L are losses, G is Gain, and P_t is transmit power. As you said, due to the design, you can not measure before the antenna, just afterwards. That is why I think that you have no information on the losses, have you?

    Third question: Shouldn't the transmit power of a system with three transmit antennas be thrice the single antennas' transmit power (assuming all antennas to be equal)? But no matter how I calculate it, there is no connection with factor 3. 

    Thanks in Advance, and happy easter!

    Best regards,
    Anne

  • 0 in reply to user6843
    TI__Mastermind 32905 points

    HI, Anne:

    For the AOP, I guess the important is that output EIPR  is 15dBm as shown in the data sheet.  And the other thing that is important is the radiation pattern cross different angles.   

    As you said, output EIPR is the sum of output power, antenna gains and system losses.  Can you help me understand, how the value of each portion matters?

    Best,

    Zigang

  • 0 in reply to zigang Yang
    Prodigy 170 points

    Hi Zigang,

    I try to get the facts right and close the information gap between the homepage and datasheet. There has to be a reason why you publish both data sets in different places and why they differ in their content. That is quite confusing.
    Furthermore, the single parts matter for the above-discussed calculation/Simulation and for the question of which influence each factor has. 

    For a start, it would be great to have a statement if the values on the homepage refer to a single (transmit?) antenna or the whole system (meaning the configuration of all 7 antennas).

    Best regards,
    Anne 

  • 0 in reply to user6843
    TI__Mastermind 32905 points

    HI, Anne:

    The 15dBm EIRP is refer to a single TX antenna.  And there are total 3 TX antenna. 

    Best,

    Zigang

  • 0 in reply to zigang Yang
    Prodigy 170 points

    Hey Zigang,
    Yeah, I know that. It is in the datasheet. 
    My last question refers to the values on the homepage. I try to ask it the other way round: Does the 12dBm transmit power, and the 5.2dBi gain refers to a single antenna or all antennas?
    Regards,
    Anne

  • 0 in reply to user6843
    TI__Mastermind 32905 points

    HI, Anne:

    12dBm is the transmit power per antenna for non-AOP device, which is in the datasheet for general xwr6843 device.  5.2dB antenna gain refers to single TX antenna gain.   

    Best,

    Zigang

  • 0 in reply to zigang Yang
    Prodigy 170 points

    Hi Zigang,
    Thanks for that clarification and your patience with my questions.
    Regards,
    Anne