Summary form only given. Single Langmuir probe (SLP) is one of the well-known electrostatic diagnostic methods, which can measure various plasma parameters, such as electron temperature, plasma density, and plasma potential. However, the SLP cannot be applied in some plasmas, such as dust plasmas and processing plasmas containing deposition gases or dust particles, without probe tip cleaning. To overcome the weakness of the SLP, a floating harmonic method (FHM) has been recently developed and extended researches based on the FHM have been studied. This FHM measures plasma parameters using the relation between a fundamental frequency current and a second harmonic current, and thus, a careful consideration for the stray current is needed when the FHM is used. In this study, a sideband method (SBM), which is based on the FHM but no consideration of the stray current, is studied and the comparisons of the measured electron temperature and the plasma density from the conventional FHM and the SBM are investigated. The SBM can be helpful to the plasma diagnostics for the large-area plasma reactor or fusion device reactor, which has a long measurement cable length or a large amount of the stray current.
