Commodity software steerable antennas for mesh networks Jim Kajiya MSR

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.

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

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

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

Coplanar Waveguide (CPW) Phase shifter Dielectric

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

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

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.

Simulation of 4 element patch Beam Patterns

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