coaxial waveguides; microstrip lines; power dividers; substrate integrated waveguides; waveguide transitions; coaxial waveguide; coaxial-SIW transition structure; eight way power divider; hybrid waveguide power divider; microstrip line power divider; phase balance; substrate integrated waveguide; Cavity resonators; Microwave amplifiers; Microwave circuits; Microwave filters; Power dividers; Substrates; Yttrium; Substrate Integrated Waveguide (SIW); coaxial waveguide power divider; eight-way;