UNIT-1 - BASIC MICROWAVE COMPONENTS
INTRODUCTION TO F MICROWAVE ENGINEERING
Modern electromagnetic theory was formulated in 1873 by James Clerk Maxwell solely from mathematical considerations. Maxwell’s formulation was cast in its modern form by Oliver Heaviside, during the period 1885 to 1887.Heinrich Hertz, a German professor of physics understood the theory published by Maxwell, carried out a set of experiments during 1887-1891 that completely validated Maxwell’s theory of electromagnetic waves. It was only in the 1940’s (World War II) that microwave theory received substantial interest that led to radar development. Communication systems using microwave technology began to develop soon after the birth of radar. The advantages offered by microwave systems, wide bandwidths and line of sight propagation, provides an impetus for the continuing Development of low cost miniaturized microwave components. APPLICATIONS OF MICROWAVE ENGINEERING
* Antenna gain is proportional to the electrical size of the antenna. At higher frequencies, more antenna gain is therefore possible for a given physical antenna size, which has important consequences for implementing miniaturized microwave systems. * More bandwidth can be realized at higher frequencies. Bandwidth is critically important because available frequency bands in the electromagnetic spectrum are being rapidly depleted. * Microwave signals travel by line of sight are not bent by the ionosphere as are lower frequency signals and thus satellite and terrestrial communication links with very high capacities are possible. * Effective reflection area (radar cross section) of a radar target is proportional to the target’s electrical size. Thus generally microwave frequencies are preferred for radar systems * Various molecular, atomic, and nuclear resonances occur at microwave frequencies, creating a variety of unique applications in the areas of basic science, remote sensing, medical diagnostics and treatment, and heating methods. * Microwave communication systems handle a large fraction of the world’s international and other long haul telephone, data and television transmissions.
MICROWAVE TELECOMMUNICATION TOWER
* Most of the currently developing wireless telecommunications systems, such as direct broadcast satellite (DBS) television, personal communication systems (PCSs), wireless local area networks (WLANS), cellular video (CV) systems, and global positioning satellite (GPS) systems rely heavily on microwave technology. USES
* Before the advent of fiber optic transmission, most long distance telephone calls were carried via microwave point-to-point links through sites like the AT&T Long Lines. Starting in the early 1950's, frequency division multiplex was used to send up to 5,400 telephone channels on each microwave radio channel, with as many as ten radio channels combined into one antenna for the hop to the next site, up to 70 km away. * Wireless LAN protocols, such as Bluetooth and the IEEE 802.11 specifications, also use microwaves in the 2.4 GHz ISM band, although 802.11a uses ISM band and U-NII frequencies in the 5 GHz range. Licensed long-range (up to about 25 km) Wireless Internet Access services can be found in many countries (but not the USA) in the 3.5–4.0 GHz range. * Metropolitan Area Networks: MAN protocols, such as WiMAX (Worldwide Interoperability for Microwave Access) based in the IEEE 802.16 specification. The IEEE 802.16 specification was designed to operate between 2 to 11 GHz. The commercial implementations are in the 2.3GHz, 2.5 GHz, 3.5 GHz and 5.8 GHz ranges. * Wide Area Mobile Broadband Wireless Access: MBWA protocols based on standards specifications such as IEEE 802.20 or ATIS/ANSI HC-SDMA (e.g. iBurst) are designed to operate between 1.6 and 2.3 GHz to give mobility and in-building penetration characteristics similar to mobile phones but with...
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