+ Post New Thread
Results 1 to 8 of 8
  1. #1
    Newbie level 4
    Points: 47, Level: 1

    Join Date
    Jun 2019
    Posts
    5
    Helped
    0 / 0
    Points
    47
    Level
    1

    SMD component fixture for antenna matching prototyping

    I am currently designing an antenna that exhibits a slight capacitative reactance (54 ohm -44j)
    Since I have crude prototyping tools (a VNA and nothing more than the toner transfer method to make boards at home), I was researching a way to test and replace SMD components on the matching PCB on the fly

    The matching network uses a differential output. I need to be able to replace two capacitors and one inductor.
    I wondered if, by using vias with pins soldered into them, I could squeeze the SMD components between the two pins to test and reuse the board for other projects, (standard 50 ohm impedance and always the same f0 for all my projects)

    I don't think homemade prototype board strips would suffer many soldering cycles before breaking down.

    I would use rather big SMDs (2012 or 2520 metric)
    Is it a viable option ? or does any fixtures exist to clip SMD components in ?
    What is the standard approach ?

    Any help appreciated.

    •   AltAdvertisement

        
       

  2. #2
    Advanced Member level 4
    Points: 6,247, Level: 18
    kripacharya's Avatar
    Join Date
    Dec 2012
    Location
    New Delhi
    Posts
    1,209
    Helped
    182 / 182
    Points
    6,247
    Level
    18

    Re: SMD component fixture for antenna matching prototyping

    I would not recommend pressure-fit components, simply because there is a high chance of them coming loose leading to frustration.

    I always solder to ensure proper contact.

    Instead of perf boards etc, I suggest you use full clad copper with simplistic scratch-out isolation. FR4 board of course. This should be rugged enough. Your SMD components are likely to break long before the pcb does!

    - - - Updated - - -

    I would highly recommend using thru-hole ceramic caps instead of SMDs, simply because the end tags of smd caps tend to come off quite easily.

    - - - Updated - - -

    What frequency range are you working with?


    1 members found this post helpful.

  3. #3
    Advanced Member level 5
    Points: 13,695, Level: 28

    Join Date
    Apr 2014
    Posts
    2,137
    Helped
    857 / 857
    Points
    13,695
    Level
    28

    Re: SMD component fixture for antenna matching prototyping

    Quote Originally Posted by rodv92 View Post
    What is the standard approach ?
    I just solder the SMD matching components. That's fast and easy.



    •   AltAdvertisement

        
       

  4. #4
    Newbie level 4
    Points: 47, Level: 1

    Join Date
    Jun 2019
    Posts
    5
    Helped
    0 / 0
    Points
    47
    Level
    1

    Re: SMD component fixture for antenna matching prototyping

    Mainly 1.8 GHz and 2.4 GHz. I was thinking that SMD is the way to go for higher frequencies because of the parasitic effect of the through hole leads, is there a way to mitigate this ? like making a pit and not going "through the pcb" ?
    thanks.



  5. #5
    Full Member level 2
    Points: 1,042, Level: 7

    Join Date
    Oct 2017
    Posts
    145
    Helped
    20 / 20
    Points
    1,042
    Level
    7

    Re: SMD component fixture for antenna matching prototyping

    You may try wooden toothpicks with some glue. Component is glued to the toothpick and then placed to required points on PCB with slight pressure. Solder plated PCBs often have uneven surfaces, especially at the bottom side. Important PCB area and component pads may be polished with sandpapered and then covered with some flux and thin layer of solder using solder wick.



  6. #6
    Advanced Member level 5
    Points: 39,330, Level: 48

    Join Date
    Mar 2008
    Location
    USA
    Posts
    6,357
    Helped
    1853 / 1853
    Points
    39,330
    Level
    48

    Re: SMD component fixture for antenna matching prototyping

    There exist antenna-tuning (matching) RFICs, I saw this going
    on at the last "straight job" employer (although it was way
    outside my activities & interests). Can't help you with selection
    or even "who's who", but maybe the tip puts you on a path to
    getting a user-tweakable in-situ match capability which you
    can either leave in place, or substitute a fixed element when
    you are happy. Believe most such critters will use a serial link
    and a 3-5V supply (RF CMOS), so you might have to get more
    hardware on the bench, but cut-and-try would sure benefit
    from bits replacing soldering at least until you're feeling ready
    for a deeper commitment.

    The stuff I saw going past, was for low and high band cell
    phones and noises were made about integrating into RF
    switch IC products and front end modules.



  7. #7
    Advanced Member level 4
    Points: 6,247, Level: 18
    kripacharya's Avatar
    Join Date
    Dec 2012
    Location
    New Delhi
    Posts
    1,209
    Helped
    182 / 182
    Points
    6,247
    Level
    18

    Re: SMD component fixture for antenna matching prototyping

    Quote Originally Posted by dick_freebird View Post
    There exist antenna-tuning (matching) RFICs, I saw this going
    on at the last "straight job" employer (although it was way
    outside my activities & interests). Can't help you with selection
    or even "who's who", but maybe the tip puts you on a path to
    getting a user-tweakable in-situ match capability which you
    can either leave in place, or substitute a fixed element when
    you are happy. Believe most such critters will use a serial link
    and a 3-5V supply (RF CMOS), so you might have to get more
    hardware on the bench, but cut-and-try would sure benefit
    from bits replacing soldering at least until you're feeling ready
    for a deeper commitment.

    The stuff I saw going past, was for low and high band cell
    phones and noises were made about integrating into RF
    switch IC products and front end modules.
    This is an excellent suggestion !! ! I wish they had these available when we were young experimenters.

    @dick_freebird ... pleas PLEASe refer some mfgs and typical components !!



    •   AltAdvertisement

        
       

  8. #8
    Advanced Member level 5
    Points: 13,695, Level: 28

    Join Date
    Apr 2014
    Posts
    2,137
    Helped
    857 / 857
    Points
    13,695
    Level
    28

    Re: SMD component fixture for antenna matching prototyping

    From what I have seen in the past, these antenna tuner chips (e.g. Qualcomm) are essentially switched capacitor banks. So this doesn't help with the element where component value might differ most from from the precalculated ideal values: the inductor.

    As mentioned above, I don't really see the benefit of the fixture approach. After measuring the input impedance, you can do a calculation of the matching circuit, and with proper layout technique the values for C will be close. For L, you might need to go a bit smaller in nominal value due to increase of value towards SRF, but if you use manufacturer S-parameter models you can usually capture that effect well. So overall, there is not much need for swapping components.

    With a fixture, you might just introduce parasitics from the fixture, which might again change things. I think that's not a smart approach at GHz frequencies.



--[[ ]]--