Abstract: The near sensing techniques with millimeter wave play an important part in many fields. To make precise measurements of the radiometric brightness temperature of a target, one must be able to mathematically model the interaction between the electromagnetic radiation properties of the antenna and the incident radiation from the environment. This interaction can be described by Fredholm integral equation. In order to calculate the radiometric brightness temperature of a target, in this paper, a method was presented and then applied to estimate the brightness temperatures of targets in millimeter wave radiometric measurements.