A new fishnet-based waveguide metamaterial structure for the microwave region is introduced and investigated both numerically and experimentally. The proposed model is designed and fabricated on both sides of the substrate and exhibits strong metamaterial behavior (such as negative material parameters: i.e. negative permittivity, negative permeability, and negative index of refraction) at the resonance. Only one single slab is used in the simulation and experiment which provides a reduction in the number of the required samples with respect to its free-space and/or waveguide counterparts. This means that a small-sized metamaterial structure is simulated, measured, and characterized by placing the sample in the waveguide. The effective medium theory is employed for the characterization of the structure and the left-handed region is identified. The measured results are in good agreement with the simulated ones which show that the proposed structure operates well in terms of metamaterial behavior and can be used in waveguide miniaturization and waveguide-based applications such as antennas, filters, sensors, absorbers, imaging systems, and so on. To validate this claim, sensor and absorber applications are selected and the simulation results show that the proposed sensor and absorbers devices operate well under the defined conditions.