WiFi Antennas

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 3.0 108 (1 / 2.412) 10-9 m
• L (3.0 / 2.412) 10-1 m
• L 4.88 inches
• Channel 11
• L 3.0 108 (1 / 2.462) 10-9 m
• L (3.0 / 2.462) 10-1 m
• L 4.80 inches
• Split a ¼ ?
• 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 lt D lt 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 APs antenna dm
distance of mobile The mobile will see better
signal strength at distances that are multiples
of the ¼ ? 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
  shouldnt 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 cant 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.