Two novel directional couplers composing of two parallel-plate waveguides filled with layered right-handed material (RHM) and left-handed material (LHM) are proposed in this paper. Transverse magnetic (TM) modes are generated by an infinite-long line source at the input port of one waveguide. In general, the energy will be coupled into another waveguide through small holes on the common wall. Under certain conditions the energy will be enhanced in one direction which is called as the coupled port and will be isolated in another direction which is called as the isolated port. If the coupled waveguide is filled with LHM, the power density will change its direction, which is opposite to that of the coupler filled with pure RHM. If the coupled waveguide is filled with layered RHM and LHM, there will be two directional couplers simultaneously in one waveguide. Exact analysis is given and numerical results validate our conclusions.
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