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Potted 900MHz PCB antenna

Discussion in 'Electronic Design' started by Will Reeve, Oct 14, 2003.

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  1. Will Reeve

    Will Reeve Guest

    Hi,

    I have an interesting project! I am using a RF receiver device which has a
    50 Ohm RF input. I want to use a PCB printed antenna on FR4 board, not
    unusual you say. but I need to pot the whole PCB in resin to make it
    waterproof. The receiver only needs to work when floating on water! Has
    anyone any experience in PCB antenna who would be so kind to comment on the
    effects, and possible actions to counter any effects, of the potting. The
    resin is much like araldite.



    Any thoughts much appreciated.



    Will
     
  2. Hi Will,

    Look into conformal coating as an alternative. Or simply mix acetone
    and RTV to create one and paint it on. To cut down on water losses,
    it would do well to provide an air jacket around the antenna elements
    that is roughly a tenth wavelength in diameter (and from the tips).

    73's
    Richard Clark, KB7QHC
     
  3. Wayne Shanks

    Wayne Shanks Guest


    The potting compound will act as a dielectric load. My bet is that the
    dielectric constant will be about 3. Your antenna will have to shrink.
    If you know the dielectric properties of the potting compound, and
    your antenna is simple, then I might be able to run a simulation (and
    optimization) for you with IE3D.... I work with 900 MHz antennas on FR4
    every day :)

    Wayne Shanks
    Senior RF and Antenna Engineer, Matrics Inc.
     
  4. Roy Lewallen

    Roy Lewallen Guest

    If the antenna is in close proximity to water, the water's dielectric
    constant of about 80 will have a profound effect, as will its very high
    loss.

    Roy Lewallen, W7EL
     
  5. Marc H.Popek

    Marc H.Popek Guest

    www.fwt.niat.net

    This dielectric embedded antennas are smaller than naturally occurs and yet
    have a net gain
     
  6. Hi Marc,

    Interesting sentence construction.

    A cogent question would reveal some perspective: How much would your
    13dBi dielectric embedded antennas for TV Channel 2 weigh?

    73's
    Richard Clark, KB7QHC
     
  7. Dave VanHorn

    Dave VanHorn Guest

    More correctly, they CLAIM a gain, relative to isotropic.

    If the antenna is smaller than a free space antenna, then it looses capture
    area.
    I would be very interested to know how they recoup that.
    I suspect these antennas might need some power to drive an on-board
    amplifier, which means that their gain claim is bogus, and what they aren't
    telling you is that the noise floor comes up also.

    TANSTAAFL.
     
  8. They? HE (the CTO in fact). American business has a recent history
    of clown elevation.
    Capture area is hardly an issue for even the full size antennas they
    replace.
    Hi Dave,

    What is more to the matter is unstated issues of efficiency. I will
    let the claims of 8 fold boons pass (which is marketese from the world
    of ENRON). Compare these "advantages" of reclaimed volume to the
    unanswered query of weight (no claims about density are there?).

    Leftover halloween candy.

    73's
    Richard Clark, KB7QHC
     
  9. A lot less than they would for the 160 meter ham band.

    --
    Many thanks,

    Don Lancaster
    Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
    voice: (928)428-4073 email: fax 847-574-1462

    Please visit my GURU's LAIR web site at http://www.tinaja.com
     
  10. Reg Edwards

    Reg Edwards Guest

    Funnily enough, there is no decrease in capture area with simple, very small
    antennas. This is a difficult conception to get people's brains around.

    There is only a (but important) decrease in efficiency because radiation
    resistance decreases faster than the loss resistances incurred in matching
    the antenna to the receiver. Matching loss resistance increases as the
    antenna dimensions become smaller.

    For example, think in terms of the Q and loss resistance of the high
    inductance coil needed in an antenna tuner.
     
  11. Hi All, Don,

    I would least of all think that "Many thanks" was aimed specifically
    at me for such little contribution as I've offered; that aside, for
    those in the rec.radio.amateur.antenna group, I would offer that Don
    is one of the more "out of the box" technical thinkers (sorry for the
    strained expression) and I would suggest they follow the link he
    offers.

    As I have been a subscriber to Circuit Cellar since its inception,
    I've found Don's articles (and books before then) contained unique
    solutions to problems that have defied conventional analysis. Or
    rather those problems that have defied clear analysis through other's
    falling back on conventional and spontaneously dead answers.

    73's
    Richard Clark, KB7QHC
     
  12. Marc H.Popek

    Marc H.Popek Guest

    Sir Clark,

    No work on using the embedded moldable plastic dielectric at 50 Mc... as you
    point out the size and weight does not appear to be advantageous.

    However, above 900 the size shrink, has an advantage

    we have other ideas to use the FWT at lower frequencies.... stay tuned
     
  13. Marc H.Popek

    Marc H.Popek Guest

    You need to understand more about capture area effective area etc.

    The Bogus gain is relatively easy to measure, open field, sig generator two
    standard dipoles and then compare with the FWT OR

    two FWT's antennas on same range and use Friis equation to predict expected
    isotropic, then you compare with what your DUT performs ...

    It really has the gain we claim, sir!
     
  14. Marc H.Popek

    Marc H.Popek Guest

    the standard antenna's on the web site, have a weight that span from 1 oz
    to 4 oz for the smallest to biggest, respectively.

    1/2 the linear dimension = 1/8 volume if Enron's finances were this
    rudimentary, they would still be in business!

    Hey consider this,

    an antenna with 1/4 the aspect ratio (effective front viewed area) also has
    a 1/4 chance of being hit by a defined shrapnel density specified in
    military antenna requirements. AS FWT ARE smaller, they also posses a lower
    probability of damage from gunfire for a given field.
     
  15. Marc H.Popek

    Marc H.Popek Guest

    Exactly, plus consider this,

    the raditiative elements, are operating at 1/4 resonances (hence preferable
    radiation resistance and bandwidths too!) it just that they are smaller in a
    dielectric than in free space. further, the spacing between array elements,
    directors, reflectors, etc also shrink by the Er ^0.5. shrinking the
    aggregate spacing and the overall dimensions of the final antenna.

    Stayed tuned as we are releasing bi & tri band antenna's soon.

    And a host of UWB antennas. Even a UWB optimized to deposit energy inside
    of a human for echocardio-graphic imaging has UWB radar... UWB antenna
    technology is in need of standard product offerings... needs better sign
    generation too!

    I'd like to see the electronics for wi fi and uwb put onto or into the
    antenna FWET antenna modules, simplifying the critical electronics to
    antenna interface.
     
  16. Dave VanHorn

    Dave VanHorn Guest

    As it happens, I'm headed to DLS in chicago soon http://www.dlsemc.com/ ,
    and I have an application for this sort of antenna, provided it passes the
    "snake oil" test. www.mobilecommand.net

    We have a bluetooth module that could use such an antenna, as well as a
    wi-fi module coming along in the near future.

    If I can wedge it into our testing day, I wouldn't mind giving it a test,
    and reporting the results back here.
     
  17. CTO?

    What does that stand for in your organization?

    If we are to judge your product (which, by the way, has a page down):
    Seems you could have as easily claimedif, in fact, that could be achieved.

    73's
    Richard Clark, KB7QHC
     
  18. CTO,

    1 to 4 Oz at what scale and to what comparison? More ENRON marketing
    factoids. ENRON has no product offered and I notice you have no page
    of products offered either.

    Would you like to comment on how much flak your virtual designs have
    avoided here? It would seem you have the boy scout's electronics
    dictionary handy to draw terms from indiscriminately to scatter
    through these non-responsive marketing postings you are making (from
    your home computer? :)

    Sales must be extremely tenuous for you to have to find ego-salve in
    an amateur group. Let's see, a slow server, a .net domain name,
    posting business news from a private account, no products, but a lot
    of power-point presentations and you have trouble with the fundamental
    questions. All of this adds up to a vanity web site.

    Let's look at another factoid published:
    Through a search of the PTO against the name Popek we find:
    9 Popek; Marc H. (Las Vegas, NV)
    Apparatus and method for automatic climate control- filed 1994
    Phased array acoustic signal processor - filed 1988
    Impulse waveform drive apparatus for surface acoustic wave chirp
    system - filed 1988
    Process for fabricating a sculptured stripling interface conductor
    - filed 1988
    Electro-optical phase modulator - filed 1988
    Sculptured stripline interface conductor - filed 1986
    Driver unit for a laser Q-switch - filed 1985
    Linear gain voltage controlled oscillator with modulation
    compensation - filed 1983
    Frequency modulation system for a frequency synthesizer
    - filed 1984
    7 Popek; Bruce P. (South Windsor, CT)
    3 Popek; Witold J. (716 S. Milwaukee Ave., Wheeling, IL 60090)
    2 Karen Popek (Poughquag, NY)
    2 Popek; Joseph C. (Detroit, MI)
    2 Popek; Gerald J. (Los Angeles, CA)
    2 Popek; Stephen (Warren, OH)

    How does this compare with:
    12? I count 9. Wide technologies? The majority during the late 80's
    were assigned to Harris, earlier work to Motorola. The titles above
    reveal those were typically confined to one very specialized segment.
    The only antennas patented, by Bruce, not Mark, were for toys.
    Intelligent controls? HVAC comes to mind for work 10 years ago.
    Laser control and signal processing are not simple topics, but neither
    are they applicable to antennas barring unique invention - notably
    absent from the list above.

    Is this talent fungible to antennas commonly courted in this group?
    Could be, but there is clearly an absence in experience to the matter
    insofar as the grandiose credentials suggest.

    The fact of the matter is that the material presented at:
    http://www.fwt.niat.net/
    is not much more than antenna engineering samples drawn from classroom
    introductory lab work at the local University.

    73's
    Richard Clark, KB7QHC
     
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