Scientists and mathematicians of the nineteenth century laid the foundation of telecommunication and wireless technology, which has affected all facets of modern society. In 1864, James C. Maxwell put forth fundamental relations of electromagnetic ®elds that not only summed up the research ®ndings of Laplace, Poisson, Faraday, Gauss, and others but also predicted the propagation of electrical signals through space. Heinrich Hertz subsequently veri®ed this in 1887 and Guglielmo Marconi successfully transmitted wireless signals across the Atlantic Ocean in 1900. | Radio-Frequency and Microwave Communication Circuits Analysis and Design Devendra K. Misra Copyright 2001 John Wiley Sons Inc. ISBNs 0-471-41253-8 Hardback 0-471-22435-9 Electronic 1 INTRODUCTION Scientists and mathematicians of the nineteenth century laid the foundation of telecommunication and wireless technology which has affected all facets of modem society. In 1864 James C. Maxwell put forth fundamental relations of electromagnetic fields that not only summed up the research findings of Laplace Poisson Faraday Gauss and others but also predicted the propagation of electrical signals through space. Heinrich Hertz subsequently verified this in 1887 and Guglielmo Marconi successfully transmitted wireless signals across the Atlantic Ocean in 1900. Interested readers may find an excellent reference on the historical developments of radio frequencies RF and microwaves in the IEEE Transactions on Microwave Theory and Technique Vol. MTT-32 September 1984 . Wireless communication systems require high-frequency signals for the efficient transmission of information. There are several factors that lead to this requirement. For example an antenna radiates efficiently if its size is comparable to the signal wavelength. Since the signal frequency is inversely related to its wavelength antennas operating at radio frequencies and microwaves have higher radiation efficiencies. Further their size is relatively small and hence convenient for mobile communication. Another factor to favor RF and microwaves is that the transmission of broadband information signals requires a high-frequency carrier signal. In the case of a single audio channel the information bandwidth is about 20 kHz. If amplitude modulation is used to superimpose this information on a carrier then it requires at least this much bandwidth on one side of the spectrum. Further commercial AM transmission requires a separation of 10 kHz between the two transmitters. On the other hand the required bandwidth increases .
