In order to extend the speed-operation range for constant generating voltage or constant motoring power of the electrical machine, a new hybrid excitation machine with isolated magnetic paths (HEIMP) is presented in this paper. Its structure, operation mechanism, and two crucial design points are described in detail. A conceptual prototype machine is designed and manufactured in integration with a rotating-armature ac exciter (brushless). It is then simulated by finite element analysis software and tested in order to verify the efficient field-adjusting characteristics, the high efficiency, and the feasible design technique of the HEIMP machine. It is also shown that the integrated brushless design makes the system more compact and reliable.