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WiFi Antennas

WiFi Antennas Reid Palmeira EE496 Design Review Design Considerations Effectiveness SNR improvement Ideal Distance of Mobile from Base Station Size Portability Storage Cost and Build Time Realistic use Accessibility Legal Issues If the FCC comes knocking, be French: run away!

Samuel
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WiFi Antennas

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  1. WiFi Antennas Reid Palmeira EE496 Design Review

  2. Design Considerations • Effectiveness • SNR improvement • Ideal Distance of Mobile from Base Station • Size • Portability • Storage • Cost and Build Time • Realistic use • Accessibility • Legal Issues • If the FCC comes knocking, be French: run away!

  3. Design Goal • Implementation of an antenna system that provides an improved range for WiFi (802.11b) of at least 500 ft. with direct line of sight and minimal interference • Provide at least 12 dB attenuation of signal with minimal physical modification to hardware • Antennas should remain physically unobtrusive during typical operation

  4. Pringles Can Yagi • Collector length varies • Channel 1 = 2.412 GHz • Collector length = • L = 3.0 * 10^8 * (1 / 2.412) * 10^-9 m • L = (3.0 / 2.412) * 10^-1 m • L = 4.88 inches • Channel 11 = • L = 3.0 * 10^8 * (1 / 2.462) * 10^-9 m • L = (3.0 / 2.462) * 10^-1 m • L = 4.80 inches • Split a ¼ λ = • Max = 1.22” • Min = 1.20”

  5. Yagi Design • 2 sets of antennas • L = 4.88” • L = 4.80” • 3 Testing sets • Attached to mobile only – unmodified AP • Attached to AP only – unmodified mobile • Attached to both mobile and AP • Note that because the length of the array is calculated for 2.4 GHz it will work best for only 802.11b and g spec

  6. Parts and Construction • Threaded steel rod of length L and diameter approx 1/8” • Washers 1” < D < 1.5” • Matched N connector for WiFi card • Pringles can and lid • lid is used to ensure no direct contact between the array and the sides of the can that act as reflectors

  7. Parabolic Antenna – 6” The focus of the parabola is calculated as 1/f = 1/da + 1/dm f = focal point distance da = distance of parabola from the AP’s antenna dm = distance of mobile The mobile will see better signal strength at distances that are multiples of the ¼ λ it is operating at. But putting it near the focal point will improve the signal quality as well

  8. Parabolic Antenna - 9” Field strength is maximized only in the forward directions which helps improve security but as with the 6” design, the field strength varies with distances from the focus of the array.

  9. Parabolic Design • 3 Antenna sets • 2 x 6” • One on each of the AP antennas • 2 x 9” • 1 x 18” • Utilizing both AP antennas in a single array

  10. Parts and Construction • Fine wire mesh cut to D (width) x D/2 (height) • Styrofoam • Note that this is implemented only on the AP side and leave the mobile unmodified.

  11. Testing Scenarios

  12. Measurement • Primary metric for measurement is dB attenuation of the signal • Data transfer speeds can also prove useful if the antenna is merely boosting noise, the WiFi spec will assume the channel is busy and not transmit meaning data speed will lower

  13. Potential Impediments • Yagi • Loss due to coax • Unmatched N-connector • Spatial attenuation • Parabolic • Only the AP is modified, so the signal received by the mobile is still the same • Spatial attenuation

  14. Legal Considerations • FCC rules Title 47 Part 15 restricts maximum gain of non-FCC approved antennas • Limit is 20dB • I expect attenuation near 12 or 15 dB so it shouldn’t be a major concern

  15. Progress • Constructed parabolic arrays • Waiting on parts (matched N-Connectors) for the Yagi antenna. • No testing yet.

  16. Setbacks • Parts backordered • Matched connectors for Yagi array • If I can’t get the order in time or find it locally I may have to use an unmatched N connector

  17. Projected Schedule • Testing over Spring Break • Draft of report by 1 Apr.

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