Lecture 2 Radio Wave Propagaton KTH V228;lkommen till KTH講座2無線電波傳播 k V及 228；lkommen到k

1、lecture 2:radio wave propagationanders vstberg08-790 44 55vastbergkth.semaxwells equationsdfb0ebthjfdtmaxwells equations electrical field lines may either start and end on charges, or are continuous magnetic field lines are continuous an electric field is produced by a time-varying magnetic field a

2、magnetic field is produced by a time-varying electric field or by a currentradiationonly accelerating charges produce radiationsaunders, 1999uniform motionreversing directiondirection changeosscillating periodic motionpropagation mechanisms the higher frequency the more radio waves resamble the prop

3、erties of light at lower frequencies electrical properties of obstacles are important (but we tend to express these in terms of optical properties) if the wave length is of the same order of magnitude (or larger), diffraction or surface effects dominatepropagation mechanisms when the dimension of th

4、e object is: very large compared to the wavelength reflection larger compared to the wavelength diffraction small compared to the wavelength scattering very small compared to the wavelength unaffecteddiffractionsaunders, 1999propagation between two antennas (not to scale)no ground wave for frequencies 2 mhzno ionospheric wave for frequencies 30 mhzfree space propagation2244rapasprpseterrtrknife edge lossout12=4224v51