Microwave metamaterials show promise in numerous low-power applications, ranging from strip lines to antennas. In general, metamaterials allow microwave designers to obtain electromagnetic characteristics not typically available in nature, leading to new behavior as well as reductions in the size of typical devices. High-power microwave (HPM) sources were efficient in the conventional microwave source community. We consider a specific use of metamaterials as a method to reduce the size of waveguide used for power transmission, particularly, a configuration in which an array of split-ring resonators (SRRs), forming a “mu-negative” structure, allows transmission of power in a waveguide well below the cutoff frequency. This configuration would not be used in an actual HPM device, but explores the methods and considerations that might be required for developing a metamaterial structure for either making HPM sources more compact or developing new types of interaction at these high powers. For any HPM application, a microwave structure must be able to sustain high electric and magnetic fields, as well as high peak and possibly average power. The challenge for metamaterials consists of devising the subwavelength structures (a defining characteristic of metamaterials) that can sustain such fields. In particular, one must understand the sensitivity of any metamaterial system to changes in the individual elements, which in high power pertains mainly to the loss of an individual resonator element. As such a sample system, we explore the physical operating characteristics of the waveguide system loaded with an array of SRRs, particularly the role of defects on its properties. Such defects would form an important feature in any high-power application in which subwavelength structures can be damaged by high field stresses.