A waveguidebased twodimensional meniscus thin lens is proposed for mmwave quasioptical power combining in a closed structure. The proposed waveguide lens is operated in TE10 mode, and the effects of the dispersion are discussed. A matching layer is included to improve the combining efficiency. A tenway power combiner using Rexolite material is given as a designed example at 30 GHz. Simulations show that the designed meniscus lens can achieve a combining efficiency of 92.6% at the design frequency of 30 GHz, and cover the entire Kaband with more than 80% efficiency.