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A small inductively coupled plasma source has been developed for use in an ion thruster. A 10.1-mm-diameter thick film silver spiral antenna is fabricated on a low-temperature cofired ceramic with a 35-μm dielectric over the antenna. The antenna has been able to sustain an argon plasma over a frequency range from 448 to 1020 MHz with pressures ranging from 50 mtorr to 1.75 torr. Plasma start powers ranged from 3 to 50 W with minimum sustain powers down to 0.1 W. Antenna electric field measurements have been made in air and compared with simulation of the antenna field using COMSOL. These results show that the antenna pattern is dominated by the standing wave pattern of the spiral antenna. Simulations of the RF power density versus frequency compare well with the plasma start power variation except for a large start power peak between 600 and 700 MHz.