WiFi Antennas

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WiFi Antennas

• Reid Palmeira
• EE496

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WiFi Specification

• IEEE 802.11b
• Uses 2.4 GHz frequency band
• Up to 11 Mbps
• Has fallback data rates to 5.5, 2 and 1 Mbps
• Uses only Direct Sequence Spread Spectrum
• Approx. 200 ft. clear line of sight range
• 14 total channels, 11 channels (in US)

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Designs

• Pringles can
• Effective directional antenna
• Cantenna
• More effective
• Parabolic dish
• Much more effective
• Significantly improved SNR
• Limits the useful range of WiFi

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Legality Disclaimer

• Illegal by FCC regulations
• You can only attach an FCC approval antenna to a
  WiFi card or base station
• Only commercial antennas are approved
• Enforcement provisions are minimal

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Design Considerations

• Effectiveness
• SNR improvement
• Signal range improvement
• Size
• Portability
• Storage
• Cost and Build Time
• Realistic use
• Accessibility
• Legality
• If the FCC comes knocking, be French run away!

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Pringles
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Design

• N-Connector and pigtail from the reflector (the
  can) to the AP or to the WiFi card
• Mount the injector to the side of the reflector
• Parts must be checked to make sure matching
  errors dont occur for example standard coax
  cable from something like a TV will absorb the
  entire signal very quickly.
• The longer the reflector (the can) the more
  directional and less omni-directional the antenna
  becomes

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Benefits of can type booster antenna

• Improved SNR and performance
• Increase in effective range of WiFi
• Cost is much less than commercial antenna with
  similar performance
• Build and testing times are small

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Parabolic Antenna
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Design of Parabolic

• Shaped wire mesh bent over a parabolic frame to
  form a miniature grid antenna
• Mesh material should be such that
• Attached to the AP
• Focal length varies proportionally with the size
  of the mesh dish - scalability

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Benefits of parabolic design

• Increased security, since signal degrades behind
  the parabola
• Minimal parts and build time
• Significant reduction of interference
• Less parts and no N-connectors, pigtails or
  cables means no matching problems or transmission
  line worries
• No modification of any WiFi cards or modification
  to parts of the AP

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Testing with Network Stumbler
Green is signal Red is noise