To provide a waveguide which is used to connect two waveguides having different cross-sectional dimensions, has an excellent VSWR (Voltage Standing Wave Ratio) characteristic and is easily designed and manufactured, and to provide its manufacturing method.

This tapered waveguide has a simple shape obtained by connecting two straight tapered waveguides at opening ends of common dimensions. Therefore, the tapered waveguide is comparatively easy to both design and manufacture. Simultaneously, an excellent VSWR characteristic is achieved because the tapered waveguide related to this invention generates two reflected waves in an operating frequency and then offsets the reflected waves.