A plasma is produced in 1–10 mTorr Ar using 200–700 W of power at 2.45 GHz in a 20‐cm‐diam vessel. Electron cyclotron resonance (ECR) conditions are produced with an array of permanent magnets arranged over the surface of the dielectric waveguide window. No electromagnet coils are used. The microwave circuit is nonresonant and can be easily matched to the power source using an E–H waveguide tuner. The 20‐cm‐diam plasma is 16 cm long, and is surrounded mainly by grounded metal walls. The plasma expands from the ECR source region at the window and completely fills the chamber. Measurements of the electron density, electron temperature, and plasma space potential have been made as functions of spatial position using Langmuir probes. The density ranges up to 6×1011cm−3and the electron temperature is in the 2 eV range. The density axial and radial profiles are described by an ambipolar diffusion model which accounts for ionization in the bulk plasma. By applying the same permanent magnet arrangement to a rectangular waveguide, rectangular modules can be made which can be arranged in an array to produce a large‐area plasma source with independent power control for each waveguide channel.