High switching speed in next-generation power devices such as silicon carbide allows increased switching frequencies in power converters. Higher switching frequencies increase power densities, but also increase frequencies of electromagnetic noise accompanying switching operations, resulting in more serious electromagnetic interference (EMI). Radiated EMI will thus soon become a major concern when developing power converters. Most previous works have focused on conducted EMI, resulting in a dearth of research on radiated EMI from power converters. We thus investigated the generation mechanism of radiated noise from power converters to identify effective reduction methods. We identify two propagation paths of high-frequency (HF) common-mode (CM) noise currents, primary CM (PCM) and secondary CM (SCM). SCM constructs a large propagation loop, thus becoming a major source of radiated noise. To suppress HF CM current flow through each mode, we fabricate two types of CM inductors (CMI). HF CM currents are measured in a simple buck converter system. CM current measurements verify the effectiveness of CMI for reduction of HF CM currents and clarify how SCM voltage source is generated. The described generation mechanism of SCM voltage source and radiated noise is verified by measurements of radiated noise in a fully anechoic chamber.