Abstract: In quantitative microwave remote sensing applications, high-precision and highly stable blackbody radiation calibration targets are crucial for ensuring the quality of remote sensing data. Coated pyramidal arrays and inverted conical cavity microwave thermal calibration targets, as two typical calibration target structures, are widely used in imager and detector payloads, and their radiation brightness temperature performance directly determines the calibration accuracy. This study employs a multi-physics coupling analysis method, using the finite-difference time-domain method to calculate the electromagnetic characteristics of the pyramidal array and ray tracing to compute the electromagnetic characteristics of the cavity calibration target, combined with thermal simulation to obtain the temperature field distribution, systematically comparing the radiation brightness temperature performance of the two calibration targets at different frequencies. The results show that the temperature gradient of the coated pyramidal array is concentrated in the tip region. When there is a 10 K temperature difference between the substrate and the ambient background, its brightness temperature deviation reaches 0.1～0.2 K, and the bias increases significantly with coating thickness. The inverted conical cavity microwave thermal calibration target exhibits excellent brightness temperature radiation characteristics. Under an environmental temperature difference of 150 K, even with an 8 mm coating thickness taken into account, the brightness temperature bias remains below 0.05 K, showing significant advantages over the array-type pyramid calibration target. When the ambient temperature difference is less than 10 K, the brightness temperature bias can be reduced to below 0.01 K. This study analyzes the underlying physical mechanisms responsible for the differences in the radiation brightness temperature characteristics of the two calibration targets, providing a reference for the selection and performance optimization of calibration targets in microwave remote sensing.