The concrete decontamination and decommissioning (D&D) process with a finite radiating microwave source is investigated theoretically in the present paper. For the microwave induced heating pattern, the microwave field with a two-dimensional radiating source within the concrete is evaluated by solving Maxwell's equation in a near field after the waveguide. An actual microwave power dissipation is incorporated in the two-dimensional heat transfer study. The effects of microwave frequency (f), the microwave operating mode, and the thermal boundary conditions on the front wall of the concrete are fully discussed in the present analysis. Three commonly used industrial microwave frequencies of 0.896, 2.45 and 10.6 GHz were selected for the current analysis. The results reveal that as the microwave frequency increases to, or higher than 10.6 GHz, the penetration of the microwave field and the microwave power dissipation decay significantly in the wave propagation direction. As the microwave operating mode changes from TE10 to TE30, the temperature distributions become more uniform, but the value of the peak temperature decreases at the higher mode.