NATIONAL COLLEGE OF SCIENCE AND TECHNOLOGY Amafel Bldg. Aguinaldo Highway Dasmariñas City, Cavite ASSIGNMENT # 2 Microwave TechnologyRizwan, Akbar Alison October 03, 2011Communications 1/ BSECE 41A1 Score: Engr. Grace Ramones Instructor
MICROWAVE TECHNOLOGYMicrowaves are electromagnetic waves with wavelengths ranging from as long as onemeter to as short as one millimeter, or equivalently, with frequencies between 300 MHz(0.3 GHz) and 300 GHz. This broad definition includes both UHF and EHF (millimeterwaves), and various sources use different boundaries. In all cases, microwave includesthe entire SHF band (3 to 30 GHz, or 10 to 1 cm) at minimum, with RF engineeringoften putting the lower boundary at 1 GHz (30 cm), and the upper around 100 GHz(3mm).Apparatus and techniques may be described qualitatively as "microwave" when thewavelengths of signals are roughly the same as the dimensions of the equipment, sothat lumped-element circuit theory is inaccurate. As a consequence, practical microwavetechnique tends to move away from the discrete resistors, capacitors, and inductorsused with lower frequency radio waves. Instead, distributed circuit elements andtransmission-line theory are more useful methods for design and analysis. Open-wireand coaxial transmission lines give way to waveguides and stripline, and lumped-element tuned circuits are replaced by cavity resonators or resonant lines. Effects ofreflection, polarization, scattering, diffraction and atmospheric absorption usuallyassociated with visible light are of practical significance in the study of microwavepropagation. The same equations of electromagnetic theory apply at all frequencies.While the name may suggest a micrometer wavelength, it is better understood asindicating wavelengths much shorter than those used in radio broadcasting. Theboundaries between far infrared light, terahertz radiation, microwaves, and ultra-high-frequency radio waves are fairly arbitrary and are used variously between differentfields of study.Electromagnetic waves longer (lower frequency) than microwaves are called "radiowaves". Electromagnetic radiation with shorter wavelengths may be called "millimeterwaves", terahertz radiation or even T-rays. Definitions differ for millimeter wave band,which the IEEE defines as 110 GHz to 300 GHz.Above 300 GHz, the absorption of electromagnetic radiation by Earths atmosphere is sogreat that it is effectively opaque, until the atmosphere becomes transparent again inthe so-called infrared and optical window frequency ranges.
MICROWAVE TRANSMISSIONMicrowave transmission refers to the technology of transmitting information or powerby the use of radio waves whose wavelengths are conveniently measured in smallnumbers of centimeters; these are called microwaves. This part of the radio spectrumranges across frequencies of roughly 1.0 gigahertz (GHz) to 30 GHz. These correspondto wavelengths from 30 centimeters down to 1.0 cm.Microwaves are widely used for point-to-point communications because their smallwavelength allows conveniently-sized antennas to direct them in narrow beams, whichcan be pointed directly at the receiving antenna. This allows nearby microwaveequipment to use the same frequencies without interfering with each other, as lowerfrequency radio waves do. Another advantage is that the high frequency of microwavesgives the microwave band a very large information-carrying capacity; the microwaveband has a bandwidth 30 times that of all the rest of the radio spectrum below it. Adisadvantage is that microwaves are limited to line of sight propagation; they cannotpass around hills or mountains as lower frequency radio waves can.Microwave radio transmission is commonly used in point-to-point communicationsystems on the surface of the Earth, in satellite communications, and in deep spaceradio communications. Other parts of the microwave radio band are used for radars,radio navigation systems, sensor systems, and radio astronomy.The next higher part of the radio electromagnetic spectrum, where the frequencies areabove 30 GHz and below 100 GHz, are called "millimeter waves" because theirwavelengths are conveniently measured in millimeters, and their wavelengths rangefrom 10 mm down to 3.0 mm. Radio waves in this band are usually strongly attenuatedby the Earthly atmosphere and particles contained in it, especially during wet weather.Also, in wide band of frequencies around 60 GHz, the radio waves are stronglyattenuated by molecular oxygen in the atmosphere. The electronic technologies neededin the millimeter wave band are also much more difficult to utilize than those of themicrowave band.Properties Suitable over line-of-sight transmission links without obstacles Provides large useful bandwidth when compared to lower frequencies (HF, VHF, UHF) Affected by the refractive index (temperature, pressure and humidity) of the atmosphere, rain (see rain fade), snow and hail, sand storms, clouds, mist and fog, strongly depending on the frequency.
USES[Wireless]] transmission of information One-way (e.g. television broadcasting) and two-way telecommunication using communications satellite Terrestrial microwave radio broadcasting relay links in telecommunications networks including e.g. backbone or backhaul carriers in cellular networks linking BTS-BSC and BSC-MSC.Wireless transmission of power Proposed systems e.g. for connecting solar power collecting satellites to terrestrial power gridsParabolic (microwave) antennaTo direct microwaves in narrow beams for point-to-point communication links or radiolocation(radar, a parabolic antenna is usually used. This isan antenna that uses a parabolic reflector to directthe microwaves. To achieve narrow beamwidths,the reflector must be much larger than thewavelength of the radio waves. The relativelyshort wavelength of microwaves allows reasonablysized dishes to exhibit the desired highlydirectional response for both receiving andtransmitting.
MICROWAVE POWER TRANSMISSIONMicrowave power transmission (MPT) is the use of microwaves to transmit powerthrough outer space or the atmosphere without the need for wires. It is a sub-type ofthe more general wireless energy transfer methods.HistoryFollowing World War II, which saw the development of high-power microwave emittersknown as cavity magnetrons, the idea of using microwaves to transmit power wasresearched. In 1964, William C. Brown demonstrated a miniature helicopter equippedwith a combination antenna and rectifier device called a rectenna. The rectennaconverted microwave power into electricity, allowing the helicopter to fly. In principle,the rectenna is capable of very high conversion efficiencies - over 90% in optimalcircumstances.Most proposed MPT systems now usually include a phased array microwave transmitter.While these have lower efficiency levels they have the advantage of being electricallysteered using no moving parts, and are easier to scale to the necessary levels that apractical MPT system requires.Using microwave power transmission to deliver electricity to communities withouthaving to build cable-based infrastructure is being studied at Grand Bassin on ReunionIsland in the Indian Ocean.During the Cold War, the US intelligence agencies, such as NSA, were reportedly able tointercept Soviet microwave messages using satellites such as Rhyolite. Microwavealso used in mobile communication.Common safety concernsThe common reaction to microwave transmission is one of concern, as microwaves aregenerally perceived by the public as dangerous forms of radiation - stemming from thefact that they are used in microwave ovens. While high power microwaves can bepainful and dangerous as in the United States Militarys Active Denial System, MPTsystems are generally proposed to have only low intensity at the rectenna.Though this would be extremely safe as the power levels would be about equal to theleakage from a microwave oven, and only slightly more than a cell phone, the relativelydiffuse microwave beam necessitates a large rectenna area for a significant amount ofenergy to be transmitted.Research has involved exposing multiple generations of animals to microwave radiationof this or higher intensity, and no health issues have been found
Proposed usesMPT is the most commonly proposed method for transferring energy to the surface ofthe Earth from solar power satellites or other in-orbit power sources. MPT isoccasionally proposed for the power supply in [beam-powered propulsion] for orbital liftspace ships. Even though lasers are more commonly proposed, their low efficiency inlight generation and reception has led some designers to opt for microwave basedsystems.Current statusWireless Power Transmission (using microwaves) is well proven. Experiments in thetens of kilowatts have been performed at Goldstone in California in 1975 and morerecently (1997) at Grand Bassin on Reunion Island. In 2008 a long range transmissionexperiment successfully transmitted 20 watts 92 miles (148 km) from a mountain onMaui to the main island of Hawaii
MICROWAVE RADIO RELAYMicrowave radio relay is a technology for transmitting digital and analog signals, suchas long-distance telephone calls and the relay of television programs to transmitters,between two locations on a line of sight radio path. In microwave radio relay, radiowaves are transmitted between the two locations with directional antennas, forming afixed radio connection between the two points. Long daisy-chained series of such linksform transcontinental telephone and/or television communication systems.How microwave radio relay links are formedBecause a line of sight radio link is made, the radio frequencies used occupy only anarrow path between stations (with the exception of a certain radius of each station).Antennas used must have a high directive effect; these antennas are installed inelevated locations such as large radio towers in order to be able to transmit across longdistances. Typical types of antenna used in radio relay link installations are parabolicreflectors, shell antennas and horn radiators, which have a diameter of up to 4 meters.Highly directive antennas permit an economical use of the available frequencyspectrum, despite long transmission distances.Planning considerationsBecause of the high frequencies used, a quasi-optical line of sight between the stationsis generally required. Additionally, in order to form the line of sight connection betweenthe two stations, the first Fresnel zone must be free from obstacles so the radio wavescan propagate across a nearly uninterrupted path. Obstacles in the signal field causeunwanted attenuation, and are as a result only acceptable in exceptional cases. Highmountain peak or ridge positions are often ideal: Europes highest radio relay station,the Richtfunkstation Jungfraujoch, is situated atop the Jungfraujoch ridge at an altitudeof 3,705 meters (12,156 ft) above sea level.Obstacles, the curvature of the Earth, the geography of the area and reception issuesarising from the use of nearby land (such as in manufacturing and forestry) areimportant issues to consider when planning radio links. In the planning process, it isessential that "path profiles" are produced, which provide information about the terrainand Fresnel zones affecting the transmission path. The presence of a water surface,such as a lake or river, in the mid-path region also must be taken into consideration asit can result in a near-perfect reflection (even modulated by wave or tide motions),creating multipath distortion as the two received signals ("wanted" and "unwanted")swing in and out of phase. Multipath fades are usually deep only in a small spot and anarrow frequency band, so space and/or frequency diversity schemes would be appliedto mitigate these effects.
The effects of atmospheric stratification cause the radio path to bend downward in atypical situation so a major distance is possible as the earth equivalent curvatureincreases from 6370 km to about 8500 km (a 4/3 equivalent radius effect). Rare eventsof temperature, humidity and pressure profile versus height, may produce largedeviations and distortion of the propagation and affect transmission quality. Highintensity rain and snow must also be considered as an impairment factor, especially atfrequencies above 10 GHz. All previous factors, collectively known as path loss, make itnecessary to compute suitable power margins, in order to maintain the link operativefor a high percentage of time, like the standard 99.99% or 99.999% used in carrierclass services of most telecommunication operators. [[File:TV remote pickup Pier 88jeh.JPG|thumb|left|Portable microwave rig for Electronic news gathering (ENG) fortelevision newsOver-horizon microwave radio relayIn over-horizon, or tropospheric scatter, microwave radio relay, unlike a standardmicrowave radio relay link, the sending and receiving antennas do not use a line ofsight transmission path. Instead, the stray signal transmission, known as "tropo -scatter" or simply "scatter," from the sent signal is picked up by the receiving station.Signal clarity obtained by this method depends on the weather and other factors, andas a result a high level of technical difficulty is involved in the creation of a reliable overhorizon radio relay link. Over horizon radio relay links are therefore only used wherestandard radio relay links are unsuitable (for example, in providing a microwave link toan island).USAGE OF MICROWAVE RADIO RELAY SYSTEMSDuring the 1950s the AT&T Communications system of microwave radio grew to carrythe majority of US Long Distance telephone traffic, as well as intercontinental televisionnetwork signals. The prototype was called TDX and was tested with a connectionbetween New York City and Murray Hill, the location of Bell Laboratories in 1946. TheTDX system was set up between New York and Boston in 1947. The TDX was improvedto the TD2, which still used klystrons, and then later to the TD3 that used solid stateelectronics. The main motivation in 1946 to use microwave radio instead of cable wasthat a large capacity could be installed quickly and at less cost. It was expected at thattime that the annual operating costs for microwave radio would be greater than forcable. There were two main reasons that a large capacity had to be introducedsuddenly: Pent up demand for long distance telephone service, because of the hiatusduring the war years, and the new medium of television, which needed more bandwidththan radio.Similar systems were soon built in many countries, until the 1980s when the technologylost its share of fixed operation to newer technologies such as fiber-optic cable andoptical radio relay links, both of which offer larger data capacities at lower cost per bit.
Communication satellites, which are also microwave radio relays, better retained theirmarket share, especially for television.At the turn of the century, microwave radio relay systems are being used increasingly inportable radio applications. The technology is particularly suited to this applicationbecause of lower operating costs, a more efficient infrastructure, and provision of directhardware access to the portable radio operator.Microwave linkA microwave link is a communications system that uses a beam of radio waves in themicrowave frequency range to transmit video, audio, or data between two locations,which can be from just a few feet or meters to several miles or kilometers apart.Microwave links are commonly used by television broadcasters to transmit programmesacross a country, for instance, or from an outside broadcast back to a studio.Mobile units can be camera mounted, allowing cameras the freedom to move aroundwithout trailing cables. These are often seen on the touchlines of sports fields onSteadicam systems.Properties of microwave links Involve line of sight (LOS) communication technology Affected greatly by environmental constraints, including rain fade Have very limited penetration capabilities through obstacles such as hills, buildings and trees Sensitive to high pollen count Signals can be degradedduring Solar proton events Uses of microwave links In communications between satellites and base stations As backbone carriers for cellular systems In short range indoor communicationsTunable microwave deviceA tunable microwave device is a device that works at radio frequency range with thedynamic tunable capabilities, especially an electric field. The material systems for such adevice usually have multilayer structure. Usually, magnetic or ferroelectric film on ferriteor superconducting film is adopted. The former two are used as the property tunablecomponent to control the working frequency of the whole system. Devices of this typeinclude tunable varators, tunable microwave filters, tunable phase shifters, and tunableresonators. The main application of them is re-configurable microwave networks, forexample, reconfigurable wireless communication, wireless network, and reconfigurablephase array antenna