Antenna for 433MHz

Discussion in 'Wireless & RF Design' started by rjjenkins, Jun 24, 2014.

  1. rjjenkins

    Thread Starter Member

    Apr 16, 2011
    102
    2
    Hello

    I've a query about antennas. I'm building something that I need to be really small, about 1.2cm cubed, and which includes a 433MHz ASK transmitter. I'm using a very small transmitter chip, very basic, from Radiotronix, which is about 6mm x 4mm. It all works fine but I have a problem with the antenna. I had hoped that I could use enamelled wire of the right length (i.e. about 17cm) and wrap it round itself, so it can fit in the 1.2cm cube. Unfortunately this drastically reduces the range so it is really unuseable. This is all very rough and ready, and I'm wondering whether I might get a better result if I made a kind of trace antenna on a PCB, and if so if there is one pattern that might work better than another. Or is there another solution altogether? I know that a higher frequency transmitter would need a shorter antenna but I don't know if there is anything out there as small as I have got.

    Thanks
     
  2. dougc314

    Member

    Dec 20, 2013
    38
    11
  3. vk6zgo

    Active Member

    Jul 21, 2012
    677
    85
    No matter what you use in that limited size,they will be pretty uniformly lousy.
    The wavelength of a 433MHz signal is round about 70cm,so any antenna is going to be a very small fraction of any resonant length.

    Antennas have a very unforgiving rule of thumb----very small compared to a wavelength = very poor efficiency,& no special "magic" can change that!:D
     
  4. rjjenkins

    Thread Starter Member

    Apr 16, 2011
    102
    2
    How do chip antennas work? They do look like a kind of magic or are they just long antennas wound back on themselves?
     
  5. vk6zgo

    Active Member

    Jul 21, 2012
    677
    85
    My guess is very inefficient antennas with a good matching system!
    (maybe active matching?)

    You can make "normal mode"helical antennas with a long conductor wound into a coil,but "winding it back on itself" will cause signal cancellation.

    "Fractal antennas" are another design which is said to be useful,but many antenna authorities say they have no advantages over standard types.
     
  6. rjjenkins

    Thread Starter Member

    Apr 16, 2011
    102
    2
    Thanks. I've ordered a chip and will see.
    But if I stick with wire, it looks like the best bet is probably to wrap is as spherically as possible around everything else, to minimise doubling back and maximise omnidirectionality?
     
  7. dougc314

    Member

    Dec 20, 2013
    38
    11
    One thing that the chip antennas do is use a ceramic material that has a dielectric coefficient much much greater than air (20 to 110) according to Kyocera). The antenna structures built with those materials gets smaller by the square root of the ratio to more common pc board materials (4-10). That means that they can make the structure have a greater effective area, and better gain than you would expect from its physical size.

    They are termed dielectric resonator antennas and there is a wikipedia article on them.
     
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  8. Papabravo

    Expert

    Feb 24, 2006
    10,138
    1,786
    If they work at much higher frequencies than 433 MHz then they can be smaller.
     
  9. rjjenkins

    Thread Starter Member

    Apr 16, 2011
    102
    2
    It turned out to be surprisingly effective. Only 12 mm long but as good as, if not better than, my previous attempts with wire of the "correct" length.
     
  10. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    2,039
    287
    Fortunately for such applications, you only NEED a lousy antenna. :)
     
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