• State
  • Locked Locked
  • Replies 6 replies
  • Subscribers 9 subscribers
  • Views 2582 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DN031 expected antennae ranges

Kenny Tay
Intellectual 970 points

I've been developing custom boards with the designs from DN031. In the design note, I see good numbers for gain and directivity but how do these numbers translate to physical range with line of sight? The reason I am asking this is because I have made custom boards for #6 and #10 from DN024 and observed a huge difference in range:

  • Board #6 (90% efficiency): Range of 100m LOS
  • Board #10 (60% efficiency): Range of 10m LOS

I understand that efficiency is squared since it affects both the receiver and the sender but a drop from 100m to 10m seems too large.

In addition, I see the note from DN031 mentioning that the antenna needs to be tuned. Am I required to change the values of Z101 - Z104? Or are they fine as is? Currently, I am using the exact components for Z101 - Z104 as stated in DN031. Also, not sure if this matters but instead of doing impedance matching with multiple discrete components, I am using a 915 MHz balun from Johanson.

FYI, we don't have a network analyzer here so I am contemplating getting external help to tune my antenna. Or if it is even possible to tune it to increase its range. Lastly, if anyone has a good contact for antenna tuning in Shenzhen, please send me an IM!

  • 0
    TI__Mastermind 33080 points
    Hi,

    A good antenna document is the DN035 (www.ti.com/cn/lit/pdf/swra351) which is basically an overview of all the antennas designs available from TI.

    If you have space available then board #6 is the best solution and this is quite insensitive to matching and has a good bandwidth; ideal when you do not have a VNA. Board #10 is more sensitive since it is more dependent on the antenna match and has a smaller bandwidth.

    For the range expectation, check out the excel sheet to make a realistic calculation. With this tool, then you can add different antenna efficiencies and see the effects it has on the range.

    Excel range sheet: e2e.ti.com/.../375556

    Regards,
    Richard
  • 0 in reply to RGW
    Intellectual 970 points

    Hello Richard,

    Thanks for sharing the document. I have a few follow up questions:

    1. I assume that the "Gain in TX/RX antenna" is the value from "Gain" in section 4.8.1 in DN031. So, in the case of board #6, at 915 MHz, the gain is 2.87 dBi and for board #10, at 868 MHz, the gain is 5.16 dBi. I tried to change the value in the calculation spreadsheet as well as the gain values in the antenna lookup table but it seemed like I needed to unprotect the sheet first. Can you share the password to unprotect the sheet?
    2. If my approach to using this spreadsheet is correct, then the realistic range expectation is something in the order of 100m at 0 dBm transmission power and almost 1km at 10 dBm transmission power in LOS. If so, then the 10m range that I am seeing seems like a bug in the assembly process. Time to get cosy with my rework station again!
    3. Another difference I recall is that I was not able to get impedance matching done on the feedline for this board. With the exception of changing the thickness of the feedline, does feedline impedance matching do anything else to the PCB? The reason I ask this is because the feedline impedance match was done on my previous board, so I did not think that impedance matching was required on this board.

  • 0 in reply to Kenny Tay
    TI__Guru**** 317180 points
    Which radio do you use and which reference design are you following?
  • 0 in reply to TER
    Intellectual 970 points

    Hello TER,

    Here are the reference designs that I am following:

    1. I am developing with the CC430 at 915 MHz, so I'm using a schematic from the EM430F5137RF900.
    2. For the impedance matching circuit, I decided to go with a balun using the schematic and layout from the Johanson application note. I added the balun and the LC filter to the RF_* pins of the CC430.
    3. For the antenna, I went with Board #6 from DN031. I added the feedline and the antenna matching components as described in the design note.

    Does this combination of reference schematics make sense? In addition, I can share the gerbers with you privately if you want to take a look. Richard looked at the previous layout and has been really helpful :)

  • 0 in reply to Kenny Tay
    TI__Guru**** 317180 points
    On paper this sounds good. Do you have any equipment to do conducted measurements?

    Send me a friend request and I can take a quick look at you schematic.
  • 0 in reply to Kenny Tay
    TI__Mastermind 33080 points
    Hi,

    The gain in the excel sheet is an approximation of the antenna performance and this is more an efficiency indicator.

    Gain = n D

    with n = efficiency & D = directivity

    As an example using the previous kit antenna (CTIA OTA Report: DN613) when operating at 915 MHz, D = 3.21 dBi & n = -0.5; so the Gain will be 2.71 dBi. Operating at 868 MHz, then the gain was 1.42 dBi.

    For a perfect dipole with 100% efficiency the gain would be 2.1 dBi and a perfect monopole with 100% efficiency would have 5.1 dBi. However, it is important to remember that antennas do not amplify RF. Since antennas cannot create energy, the total power radiated is the same as an isotropic antenna. Any additional energy radiated in the directions it favors is offset by equally less energy radiated in all other directions.

    The exact figure of efficiency and directivity will always be layout dependent.

    Regards,
    Richard