Search

Advances in Microwave and mm-Wave Oscillator and VCO Technology Challenge System Designers' Creativity Multioctave, Microwave Gunn VCO Sources Introduction In recent years, the need for military and commercial microwave systems [...]

The theory for finding the internal field within a dielectric helix when the radiation has a wavelength larger than the diameter of the helical wire is presented. Intensities are calculated and compared to an experiment and to the theoretical results of an earlier paper that does not include the self-interaction effect. The internal field is defined in terms of a polarization matrix that is assumed to be constant across any cross section of the helix. It is found that target self-iteractions have a significant effect on the internal field. It is also noted that this effect for the far field intensities, although significant and generally a better fit to the data, is not profoundly different. That is, the effects of a more appropriately constructed internal field are less important than the geometry effect in the far field.

A method for calculating the electric field scattered from a helical dielectric target is compared to an equivalent experiment. The wavelength of the incident light is 3.18 cm, and the right-handed helix has a radius of 1.83 cm and wire radius of 0.24 cm, a pitch of 0.553 cm, and seven turns. The index of refraction of the target is 1.626−i 0.012. A brief description of the Shifrin theory generalized to this application is given along with a discussion of the experiment, and the experimental intensities are compared to the first-order theory.

The perturbation theory suggested by Shifrin is applied through the second order to the scattering of light from dielectric spheroids and finite cylinders. In the case of short dielectric cylinders, this technique provides an accurate prediction of the scattering pattern in its range of applicability, and this prediction is especially useful as no exact scattering solution exists. The validity of the perturbation theory is established by comparison with exact results for the spheroid, and excellent agreement is shown for ka(m − 1) ≈ 1, where k = 2π/λ, a is a representative target dimension, and m is the index of refraction. The results for the finite cylinder are refined from our previous work by a careful construction of the internal electrostatic solution. This allows the calculation of intensities for short cylinders. Comparisons are made between the spheroids and cylinders of equal volumes for aspect ratios ranging from ½ to 5, and significant differences are noted in some cases.

A technique for computing the electromagnetic fields scattered by spheres, cylinders, spheroids, spirals, toroids, and other targets which can be subdivided into circular disks is given. First-order calculations are performed for targets the size and refractive index of which preclude the creation of standing waves within the target. It is found that the scattering signatures of these various shapes are distinguishable for wavelengths larger than the target, but the differences rapidly diminish, as expected, with increasing wavelength. Finite cylinders are compared to prolate spheroids of equal volume, toroids are compared with oblate spheroids of equal volume, and calculations of the CIDS ratio for a spiral target are made for various wavelengths. It is found, on comparing these spiral calculations to other work on essentially 1-D spirals, that giving the spiral wire even a very small radius significantly affects the CIDS pattern for backscattering.