900 MHz Antenna for Extreme Environment

Discussion in 'Wireless & RF Design' started by NearSpaceTech, Nov 16, 2010.

  1. NearSpaceTech

    Thread Starter New Member

    Nov 7, 2010
    I am work for a company which is developing electronics for use on weather balloons. These balloons typically reach 80,000 to 100,000 ft during flight and experience severe turbulence on the way up and down. The products we develop are recovered and when there is an antenna failure the unit is lost.

    Antennas Used in the Past:
    The original antenna we was a Maxrad MTO 8903 PT patch antenna which worked great, but went out of production (with what I can gather). This was a Patch Antenna with 2.5 to 3 db in gain, 3 inches in diameter and .25 inches tall.

    The new antenna we have been using is HG905RD-RSP rubber duck antenna, which has been breaking in many different ways during flight (The most common is the plastic housing breaking off of the metal connector.) This is a 5 db antenna which works great when it is not broken during flight.

    Problem Diagnosis for “Rubber Duck Antenna”:
    There are two main factors for the failure of the Rubber Duck Antenna: 1) Length of antenna allows for lines and payloads to damage the antenna 2) The cold temperatures experienced during a flight which are many times below -40F, which causes the plastic to break.

    Antenna Solution Needed:
    Both of these factors were not a problem for our low profile patch antenna, because there was nothing to get lines caught on and if a payload hit the antenna there was almost nothing to break. We never had a patch antenna fail.

    I don’t have much experience with antennas but I have had difficulty finding a patch type antenna with more than “unity” gain. The other limitation we are dealing with is there is no ground plane for the antenna and we want to make sure we are not adding to much weight to the overall module.

    Desired Technical Specifications:
    Commercial Off the Shelf (COTS)
    Frequency Band: 900 MHz ISM Band (902-928 Mhz)
    No Ground Plane needed
    At least 2.5 db in gain
    Less than 3 inches in diameter
    Reverse SMA Connector (not critical – we can always make a different cable)

    I look forward to you feedback and insights
  2. Wendy


    Mar 24, 2008
    Given an antenna is a finely crafted piece of wire, and not much else, why not make your own?
  3. NearSpaceTech

    Thread Starter New Member

    Nov 7, 2010
    We have actually made a few different types of antenna which can work for a prototype, but we can't mass produce these in-house with quality control and to go outside to a manufacture these will cost to much.

    We would like to use an antenna that is currently on the market, in-order to ensure quality control and doge the bullet of custom antenna design and manufacturing.
  4. bertus


    Apr 5, 2008
  5. NearSpaceTech

    Thread Starter New Member

    Nov 7, 2010
    burtus - Thanks for the links. I looked at those antennas and unfortunately we could not use these because of the weight and length.

    We are hoping for a solution that is less than 1 lb and shorter the better ( less than 14in).

    Thank you for your input.
  6. Paulo540


    Nov 23, 2009
    How many of these do you need in a given month?
  7. radiohead

    Senior Member

    May 28, 2009
    Make your own antenna. 1005/900MHz = 1.11feet x 12 = 13.4 inches for a full wave antenna. 6.7 inches for half wave, and 3.35 inches for a quarter wave. You can make the antenna out of any solid core hook-up wire 26-18 AWG, or even 12 AWG Romex.

    Take apart one of those L-Com antennas and you'll see how simple they are. If the connectors are breaking off, use epoxy, hot glue or another type of strain relief to keep them from breaking off. Have you considered encapsulating your RF unit in a block of styrofoam? the weight would be negligible and shouldn't affect the performance of your radiosonde.