In this paper, the design of three-port K-band resonating filters, including an SPDT with RF MEMS switches and triangular Sierpinski-shaped resonators, has been studied. This contribution is intended to improve the performance of switched metamaterial-inspired resonators using a three-port configuration instead of a two-port structure to enhance the isolation between the resonators and the electrical matching for K-Band operation, decreasing, at the same time, the insertion losses. Electromagnetic simulations have been performed to optimize the performance of the SPDT, the individual filters, and the whole structure. Preliminary experimental results are also presented.