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I want to build a high gain directional antenna for the 915MHz frequency band. I have been looking into waveguide and yagi antennas, which seems to fulfill my gain a directional requirements but these antennae are quite large.

I know that the antenna sizes in general are dependent on wavelength, and it possible is a trade off between gain and size.

But what high gain directional antennas are generally smallest?


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    \$\begingroup\$ Gain (directionality) takes phyiscal size relative to the wavelengths. You can't cheat the laws of physics. \$\endgroup\$ Feb 16, 2013 at 14:23
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    \$\begingroup\$ Does a large array of small antennas count as small? \$\endgroup\$
    – Phil Frost
    Feb 16, 2013 at 16:45
  • \$\begingroup\$ "Loading" physical circuit elements by applying either series inductance (eg to Yagi elements)or end capacitance can reduce size at the expense of some efficiency. Also look at helical antennae. For extra points and to annoy Olin search for "Synthesised Poynting Vector" Antennas, which can be very small. Also look at the free marvellous complex NEC antenna synthesis program. \$\endgroup\$
    – Russell McMahon
    Feb 16, 2013 at 20:24

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A dielectric antenna might fit the bill.

It might be a bit hard to home-brew one, though.

Here is Toko, who make a line for GPS.

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