摘要:

We describe a step-frequency radar (SFR) imaging system that is suitable for microwave nondestructive evaluation (NDE) applications. The system includes a computer-automated microwave measurement apparatus, calibration software, and nonlinear inverse scattering imaging algorithms. Through the use of an inverse Fourier transform, the raw SFR data is transformed into a synthetic time-domain pulse. A calibration procedure involving the use of calibration targets may then be used to remove pulse distortions due to the effective aperture and dispersive nature of the antennas and measurement system. Nonlinear inverse scattering algorithms described here are then applied to the corrected data to produce quantitative spatial images of various electromagnetic parameters. Reconstructions of metallic and dielectric scattering objects including metallic rods, glass rods and plastic PVC pipes from real measurement data collected in our laboratory are shown.

ISSN:0920-5071    

DOI:10.1163/156939300X01382

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The classical Coulomb and radiation fields from a relativistic charged particle or beam of particles passing out of a conductor into vacuum are calculated in detail, and certain features are pointed out and clarified. The similar case of pulsed acceleration is also studied. For the beam case, field structure is unusual in that Coulomb fields overlap radiation fields for an extended time. Radiation fields are proportional to beam current I (t) , not dI /dt . It is shown that for all practical times for beams of interest, the Coulomb fields drop off like 1/R , not 1/R2. The fields evolve through an "immersion" phase where the beam is still immersed in its own radiation fields, to a "separation" phase in which the radiation field has separated from the beam. We explain how the radiation fields break away from the beam, with field lines always remaining connected. Relation to more familiar field configurations (radiation by accelerated charges, dipole radiation, transition radiation, scattering from small conductors) is discussed, and energy radiated away is calculated. A radiation formula is presented for the general case in which the net current profile changes as the beam propagates (in air). We also discuss beams exiting an openended pipe. It is shown that the maximum radiation angle, = 1/γ, has a simple physical, geometric origin. Likewise the maximum angle of a longitudinally accelerated charge is shown to have a similar, readily understood, physical origin, making it intuitively clear why an accelerated electron radiates most at the angle ~ 1/2γ .

ISSN:0920-5071    

DOI:10.1163/156939300X01391

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We develop a numerical solution to the scattering problem with regard to perpendicularly crossed multilayered strip gratings. This structure is regarded as a microscopic model of electromagnetic wave absorbing sheet of the fiber type. The boundary value problem is formulated into the set of integral equations, which is discretized to the linear equations by applying the moment method. Numerical computation is carried out for the distribution of the incident power to the reflected, transmitted, and absorbed powers. The absorbing rate exceeds 94% by a proper choice of grating parameters. The equivalent circuit parameters of the crossed resistive grating is also obtained.

ISSN:0920-5071    

DOI:10.1163/156939300X01409

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In this paper, a vector wave function expansion of dyadic Green's functions is made to characterize electromagnetic waves in lossless, reciprocal and homogeneous chirowaveguides. Using orthogonalities among these vector wave functions, the Ohm-Rayleigh expansion, and the method of Gm, we represent the Green's dyadic in terms of the modified vector wave functions. It is realized that the conventional procedure of the vector wave expansion described in the normal texts cannot be directly applied to the formulation of the Green's dyadic in chirowaveguides. Some generalized orthogonalities among these vector wave functions in the chirowaveguides have to be considered when deriving the dyadic Green's functions. References

ISSN:0920-5071    

DOI:10.1163/156939300X01418

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A Physical Optics approximation is applied to evaluate the Radar Cross Section of polygonal flat-plate structures with dielectric parts. Suitable closed form expressions for the field scattered in the far zone are provided. Samples of numerical results are shown with reference to simple configurations to discuss the application of the proposed procedure.

ISSN:0920-5071    

DOI:10.1163/156939300X01427

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A method for the prediction of the slant path rain attenuation statistics is proposed, based on the Weibull distribution for the representation of the point rainfall rate statistics. The inhomogeneity of the rainfall medium is described by means of the spatial autocorrelation function. Numerical results derived by using the proposed model have been compared with available experimental data taken from the most recent ITU-R database. Comparison is also made with another prediction method recommended by the International Radio Consultative Committee and some useful conclusions are deduced. More particularly, the present method has been found to give improved results for the higher percentages of time. On the other hand, the CCIR method is superior for the lowest levels (0.003% and 0.001%) .

ISSN:0920-5071    

DOI:10.1163/156939300X01436

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

By using transmission line theory, contributions to the output from a right angle bend are extracted explicitly for a microstrip line of printed circuit board. A simplified approach to the signal integrity for a three-conductor printed circuit board is presented. Parameters to estimate rings caused by reflections are derived. Numerical results for the above discussions agree well with the symbolic solutions.

ISSN:0920-5071    

DOI:10.1163/156939300X01445

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939300X01454

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939300X01463

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor