This paper develops a compact microwave plasma torch (CMPT) operating at 2.45 GHz with an ultrabandwidth of 30 MHz.  The structure and equivalent circuit of CMPT is established and analyzed based on theory of transmission line.  The effects of different microwave powers on the CMPT discharge are carried out on this system.  Finally, in order to demonstrate the performance of the CMPT, an experiment to modify the surface of polymethyl methacrylate (PMMA) is conducted.  It is found that the water contact angle is reduced from 85.4° to 32.3°, and the surface morphology characterized by atomic force microscope indicates significant improvement of the surface wettability of PMMA, which proves that the CMPT system is feasible and available.
CMPT
The simulation results indicate that the resonant frequency will drift downward with the presence of plasma. 
The simulation results indicate that the resonant frequency will drift downward with the presence of plasma.