Commodity software steerable antennas for mesh networks

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Commodity software steerable antennas for mesh
networks

• Jim Kajiya
• MSR

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Why software steerable antennas?

• High gain antenna significantly improves mesh
  networks.
• Narrow beam antennas are key to network topology
  control for minimizing interference.
• High gain, low sidelobe design enables indoor
  placement
• Software antenna control integrates routing and
  propagation.
• Much nearer term than smart antennas/MIMO.

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Challenges for steerable antennas in mesh networks

• Exacerbates hidden terminal problem
• FCC regulations for unlicensed bands limit ERP
• Aimed at access point abuse, current regulations
  preclude neighborhood mesh
• Cost increment over omni
• High gain antenna is currently very expensive

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First Prototype

• 8x8 dipole array
• Designing feed network was the hard part

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Phased array Antenna

• Induce time delays
• Phase shifters are currently expensive

d
2d
3d
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Coplanar Waveguide (CPW) Phase shifter
Dielectric
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CPW Phase shifter uses elementary transmission
line physics

• Delay is given by
• Impedance is given by
• As distance varies relative permittivity changes

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Simulation Results

• Phase shifter design is best done with dielectric
  penetrating the air gap in a coplanar waveguide.

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Simulation Results, contd

• High dielectric constant material not necessary
  alumina with 10 is fine.
• Variable characteristic impedance does not
  materially affect antenna pattern or VSWR.

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Simulation of 4 element patch Beam Patterns
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Next Design

• Coplanar Waveguide phase shifters compatible with
  corporate feed.
• Form factor for indoor wall mounting