Radio Wave Transmission
Radio systems form part of our daily routine and their applications are diverse. Examples include (i) long range and short range radio communications and on-body radio networks, (ii) radio imaging, (iii) radio remote sensing and (iv) radio frequency identification. The successful implementation of such systems requires knowledge of how radio waves are transmitted in various media and the available power to the receiver. Transmission loss, also known as path loss or attenuation, refers to the gradual loss of power density of a signal in a medium. This phenomenon applies to a number of areas other than radio transmission, such as the attenuation of sound and light in sea water, and losses over an optical link or electric power transmission line. Attenuation in a radio or an optical fibre link limits the rate of digital data transmission and hence has to be taken into account when designing a communication system. While in optical fibre the main source of attenuation is due to scattering, a number of factors contribute to transmission loss of radio waves such as atmospheric effects, terrain and propagation through buildings. Estimation of transmission loss is important in ensuring an acceptable quality of service by locating transmitters at appropriate locations and with appropriate power levels to provide coverage over the desired geographic area.
This chapter discusses transmission loss starting with the basic form of propagation in free space to ...