1. Commodity software steerable antennas for mesh networks
Jim Kajiya
MSR

2. 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.

3. 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

4. First Prototype 8x8 dipole array
Designing feed network was the hard part

5. Phased array Antenna Induce time delays
Phase shifters are currently expensive d 2d 3d

6. Coplanar Waveguide (CPW) Phase shifter
Dielectric

7. CPW Phase shifter uses elementary transmission line physics
Delay is given by
Impedance is given by
As distance varies relative permittivity changes

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

9. Simulation Results, cont’d
High dielectric constant material not necessary: alumina with =10 is fine.
Variable characteristic impedance does not materially affect antenna pattern or VSWR.

10. Simulation of 4 element patch Beam Patterns

11. Next Design
Coplanar Waveguide phase shifters compatible with corporate feed.
Form factor for indoor wall mounting