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For weak scatterers, simple relations have been discovered between physical properties and the Fourier transforms of their scattering fields, but they are invalid under strong-scattering conditions. In this paper, a microwave networking technique is used to investigate the one-dimensional inverse scattering problem, from which a novel inverse scattering solution for the permittivity profile is derived by considering the equivalent microwave network of the permittivity profile discontinuity at the interface of free space with the medium. This novel solution is essentially different from previous relations and is valid for both weak-scattering and strong-scattering conditions. Closed-form and numerical reconstruction examples show that the novel solution is accurate in comparison with exact theory and is applicable to both continuous and discontinuous permittivity profiles.

The multilayered medium modelled by the Cantor bar is a kind of self-similar structure, which has found wide applications in some optical and quantum areas. In this paper, reflection and transmission properties of arbitrary fractal Cantor bar layers are investigated first by using a self-similar networking method. Furthermore, the inverse scattering approach for this fractal structure is then researched, in which the fractal dimension, the dielectric characteristics, and the self-similar structure of the fractal system are reconstructed from the reflection spectrum illuminated by a normally incident plane-polarized electromagnetic wave. Some reconstruction examples are given to show the validity of this method.

The time-domain characteristics of terahertz radiations emitted from a biased large-aperture photoconductive antenna trigged by an ultra-short optical pulse are studied. Succinct explicit expressions in the surface field and in the far field for the emitted THz radiation fields are deduced based on the well-known current-surge model. The expressions indicate that the THz radiations in the surface and far fields are mainly affected by the incident light intensity, the incident light wavelength, the carrier relaxation time, the reflectivity illuminated at the photoconductor, the carrier lifetime, and the incident light pulse width. The characteristics of THz radiation in the surface and far fields are discussed, and the phenomena of changes in the radiation peak values, the radiation pulse width, and the rising edges are explained in details. Especially the changes in surface fields are explained with the increasing of the ratio of luminous flux. The numerical results indicate that the emitted THz radiation intensity can be increased by enhancing the ratio of luminous flux, prolonging the carrier lifetime, or reducing the incident light pulse width. To avoid the shielding effect of the radiation field, an effectively method is presented that the intense of the incident laser pulse could be divided into multiple beams with low energy to trigger the photoconductive antenna, thus the THz radiation power can be further increased significantly.