tailieunhanh - Electromagnetic Waves Propagation in Complex Matter Part 11

Tham khảo tài liệu 'electromagnetic waves propagation in complex matter part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 7 Field Estimation through Ray-Tracing for Microwave Links Ada Vittoria Bosisio National Research Council of Italy CNR IEIIT c o Politecnico di Milano Italy 1. Introduction Engineers using microwave radio links have to address the effects of multipath propagation that arise when several rays arrive at the receiver after travelling along different paths from the transmitter. Rays along their propagation undergo reflections at the earth s surface or at variations in the refractive index or its gradient. Since the 60s standard ray theories for radio wave applications use effective earth radius concepts ray bending based on Snell s law in a layered spherical atmosphere or analytical method limited to simple refractive index profiles Du Castel 1966 Livingston 1970 . At that time scientists were interested in statistics of fading distinguishing between fast or slow fading and the typical results were either nomograms of attenuation as a function of distance for a set of common frequency and height values or cumulative distribution functions representing the fraction of time that the signal was expected to be received at or below a given level CCIR 1978 . Several techniques were employed to calculate the field strength such as Cornu s spiral derived by the Huygens principle together with the introduction of the specular and the diffuse reflection contribution Hall 1979 . In that approach the field amplitude was determined assuming the principle of conservation of energy . the flux of the energy along a ray is the same at every cross section of a narrow tube of rays Keller 1957 . Nowadays radio communications live a renaissance due to the development of mobile and wireless communications and the increasing demand of wideband services. The need of greater rate of transmission is accomplished using higher frequencies for which effects like the tropospheric scatter can affect dramatically the quality of the received signal. Thus aspects such as analysis of delay power .