A method is developed for computing the near field transmitted by a monomode rectangular waveguide aperture into a homogeneous lossy material. The principle of this method is discussed, and its results are verified by experiments both in an active process (when the antenna transmits a signal toward the material) and in a passive process (when the antenna receives the thermal noise transmitted by the different subvolumes of the material). The method has been applied to the computation of radiometric signals for both power and correlation radiometry. Comparison of the radiometric with experimental data points out quite a good agreement in the case of models made of water near 1.5 and 3 GHz. Consequently, this method of computing the radiometric signals can be used for medical applications, in which high-water-content tissues are often examined.
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