The concept and design of Multiple-state diplexer are explored and investigated recently due to its advantages in multiple duplexing functions integrated in a single circuit. It means that for each of the proposed multiple-state diplexer, two frequency channels can be propagated to the specific other two ports for transmitting/receiving, while the remaining ports will be isolated. Triple-state diplexer (TSD) as the simplest multiple state diplexer structure, is firstly investigated and demonstrated in the planar and waveguide structure. Each channel of the presented multiple state diplexer is followed by filtering synthesis design method so as to achieve higher order response with higher out-ofband attenuation. Simulated and measured results verify the accurate design methodology.