Cerenkov and transition radiation in space‐time periodic media

The solution to the problem of determining the radiation emitted by a uniformly moving charged particle in a sinusoidally space‐time periodic medium is obtained. The space‐time periodicity can be considered as due to a strong pump wave and is expressed as a traveling‐wave‐type change in the dielectric constant or the plasma density. The solution covers also the limiting case of sinusoidally stratified media. The expression and spectrum of the radiated electromagnetic field are determined for different media: dielectric, isotropic and uniaxial plasma. Depending on the nature of the medium and the velocity of the particle, the radiated field is of the Cerenkov and∕or transition type. The Brillouin diagram is used extensively in understanding and determining the nature, extent, and spectrum of the different modes of radiation, and a focusing effect is also studied

Magnetic wave propagation in a periodic medium

The propagation of magnetic waves in an infinite medium with a periodic dielectric constant is studied as a simplified example to evaluate the applications of periodic structures. Specifically, the use of those structures for filtering and distributed feedback is investigated, and a new scheme for the generation of magnetic waves using drifting charges and a distributed feedback configuration similar to DFB lasers is studied in some detail

Electromagnetic wave propagation and wave-vector diagram in space-time periodic media

The electromagnetic wave propagation and wave-vector diagram in generally space-time periodic dielectric, plasma, and uniaxial plasma are studied for TE and TM waves. The case of a sinusoidal periodicity is solved numerically. Special properties due to the inhomogeneity are presented

Advances In Spaceborne Active Microwave Sensing

During the 90's, a number of new capabilities and techniques will be used to observe planetary (including earth) surfaces and atmospheres with active or microwave sensors. In 1992, SIR-C will provide the capability of full imaging radar polarimetry at two frequencies L and C-band. In combination with X-SAR, simultaneous imaging at three frequencies will be possible for the first time from space. The SIR-C-XSAR is the predecessor of the EOS SAR, which in addition to the multi-frequency and multi-polarization capability, will be able to provide very wide swath (500 to 600 km) imaging at moderate resolution of few hundred meters. The EOS SAR will also be capable of radar interferometric mapping of the surface topography by using data from repeat orbits

Distributed Feedback Acoustic Surface Wave Oscillator

The application of the distributed feedback concept to generate acoustic surface waves is discussed. It is shown that surface corrugation of the piezoelectric boundary in a semiconductor-piezoelectric surface acoustic wave amplifier could lead to self-sustained oscillation

Radar Scattering from a Diffuse Vegetation Layer over a Smooth Surface

A simple model is presented for the oblique backscatter and bistatic scatter from a smooth surface overlain by a diffuse layer. Only single scattering in the diffuse layer is taken into account. The model analysis shows that the combination of volume scattering and oblique reflection at the surface may increase appreciably the waves scattering. The scattering strongly depends on the properties of the smooth surface. These results support some of the observations made with the Seasat spaceborne imaging radar over flooded regions with heavy vegetation cover

Radiation Characteristics of a Source in a Thin Substrate Mounted Over a Dielectric Medium

The radiation pattern of a line source is calculated for the case where the source is lying on the top or the bottom surface of a lossless dielectric substrate that is mounted on the top of a semi-infinite dielectric medium. It is found that in both cases the pattern along interfaces has a null; that the pattern in the upper semi-infinite medium has a single lobe; and that the pattern in the lower semi-infinite medium has many lobes, the number of which varies with the substrate thickness. It is shown that in both cases the power radiated into the lower medium is more than that radiated into the upper medium. Applications of this calculation in remote sensing, microstrip antenna technology, and antenna arrays are discussed

Coherent electromagnetic losses by scattering from volume inhomogeneities

A parametric analysis of the coherent electromagnetic losses due to scattering from volume weak inhomogeneities is reported. It is shown that even in the case of very weak inhomogeneities, the loss could be appreciable in a resonance region and thus play a more dominant role than conductivity losses

Effects of random phase changes on the formation of synthetic aperture radar imagery

The effects of Gaussian random and linear phase change on the response of the matched azimuth processor of a synthetic aperture imaging radar is analyzed numerically