The idea of similarity between the processes of electromagnetic scattering of plane waves by physical objects (scatters) in free space and the processes of scattering of quasi-optical wave beams by the same objects or their scaled patterns placed inside HDW-type QO directional structures has been used as the basis for the general approach. The waveguides of this type are featured by the presence of a hollow waveguiding channel having great electrical dimensions, which is formed by the boundary structures of different types (one-layered, multi-layered, purely dielectric, magneto-dielectric, etc.). The latter give a number of valuable properties to HDWs. Availability of the above hollow waveguiding channel is also the greatest advantage of waveguides of this type. These boundary structures, when combined with the QO principle of forming the directional modes in a waveguiding channel, make it possible to form in a quite large space domain inside the channel an electromagnetic beam with the needed quasi-optical amplitude-phase field distribution without resort to any collimators, provided that the HDW parameters and prerequisites for its excitation are chosen properly. The HDW itself plays the role of such “natural” collimator. When a studied object (a scatterer or its scaled pattern) is placed in the above-mentioned domain of a quasi-plane field it appears to be possible, provided that a number of specific requirements are satisfied, to investigate its scattering properties by measuring the scattering waveguide parameters - reflection and transmission coefficients. These latter, as the theory implies, prove to be unambiguously connected with this object's scattering characteristics in free space.
Physical principles of measuring the scattering characteristics of objects in a HDW have been devised. A new method of scaled electromagnetic modeling of the object's scattering characteristics - the quasi-optical waveguide modeling method (QWMM) - has been proposed and theoretically and experimentally justified. Here, the QWMM employs the electromagnetic properties of quasi-optical directional structures of a “hollow dielectric waveguide” type. The one-to-one correspondence between the observed quantities - the reflection and transmission coefficients of the fundamental HE11 mode at the object placed in the HDW - and the scattering characteristics of the same object in free space in the plane wave field has been established.
The theory has been developed and the principles have been elaborated dealing with the creation of a new class of radio measurement systems for scientific research and practical applications, namely, quasi-optical waveguide micro-compact ranges (MCR). They are intended for experimental study of the scattering characteristics of physical objects or their scaled patterns by the QWMM in the NMM and SMM wavelength ranges. Physically and metrologically justified criteria and requirements related to the main MCR parameters have been worked out and the corresponding techniques of parameter calculation, measurement, calibration, analysis of the performance and MCR error estimation have been developed.
The MCRs made on the basis of circular HDWs of a ”hollow dielectric beamguide” type and complexes of QO devices and components covering a wide wavelength range from 0.3 mm to 4 mm have been developed, implemented and investigated. A large body of measurements of power, amplitude-phase and polarization characteristics of direct and inverse scattering by a number of the sample objects in the NMM and SMM wavelength ranges have completely proved practical feasibility, expediency and effectiveness of the use of the QWM method.
The polarization-frequency homodyne method ensuring simultaneous and continuous measurement of all complex coefficients of a polarization scattering matrix (PSM) of the reflecting object has been proposed. The feasibility of the method, in principle, for the NMM and SMM wavelength ranges has been shown based on the QO instrumental base developed by us.
The modified polarization-frequency homodyne QWM method has been proposed and studied. It is used for investigation of the dynamic polarization characteristics of inverse scattering of the objects in a HDW. A concept of the design has been proposed and an experimental mock-up of the device has been constructed on the basis of a circular HDW and QO functional elements, which use the mentioned methods of measurement of an object's PSM in the NMM and SMM wavelength ranges.
A theory of ultra-broadband quasi-optical optimal sectional tapers (OST) for a QO system made on the basis of a HDW has been developed and experimentally approved. The feasibility and expediency of employing OST in QO systems of EDM using the QWM method are shown. A number of radio measuring schemes and QO functional devices ensuring the possibility to employ the QWM method in the NMM and SMM wavelength ranges have been proposed and implemented. The prospects of progress and extension of the developed QO methods and EMM means to the short wave part of the SMM wavelength range are studied.
The results of the studies may be widely used in the scientific and applied research aimed at the experimental study of the scattering properties of various physical objects and, in a number of cases, may be an alternative to large, sophisticated and rather costly systems used presently for these purposes.
Key words: physical electrodynamics modeling, scattering characteristics, quasi-optical structures, hollow dielectric waveguide, near millimeter and submillimeter waves.
Володимир Костянтинович Кісельов
Фізичне моделювання електромагнітного розсіювання
в квазіоптичних спрямовуючих структурах
Відповідальний за випуск Є.М. Кулешов
Підписано до друку 2002 р.
Формат 60х90/16. Папір офсет. Ум. друк. арк. 2,0. Замовлення. № 6
Тираж 100 прим.
Ротапринт ІРЕ ім. О.Я.Усикова НАН України.
м. Харків-85, вул. Акад. Проскури, 12