NATIONAL COLLEGE OF SCIENCE AND TECHNOLOGY Amafel Bldg. Aguinaldo Highway Dasmariñas City, Cavite ASSIGNMENT # 2 Microwave TechnologyBani, Arviclyn C. October 03, 2011Communications 1/ BSECE 41A1 Score: Engr. Grace Ramones Instructor
MICROWAVE DEFINITIONElectromagnetic energy with wavelengths in free space ranging roughly from 0.3 to 30 cm.Corresponding frequencies range from 1 to 100 GHz. Frequency and wavelength are related byfλ = c, where f is the frequency, λ is the free-space wavelength, and c is the velocity of light invacuum, approximately 3×108 m/s.Characteristic transmission media for microwaves are hollow-pipe waveguides, where thecross-sectional dimensions are of the order of the wavelength and thus are of convenient size.Coaxial transmission lines are also used, however, especially in the lower-frequency bands, andvarious stripline techniques are used on microwave integrated circuits. Resonant cavities arecommonly used as circuit elements, and radiation or reception of the energy is typically byhorns, parabolic reflectors, or arrays.GenerationFor most applications, microwaves are generated in electronic devices that produce oscillationsat microwave frequencies. The devices may be single-frequency or tunable, and continuous-wave (cw) or pulsed. Vacuum-tube generators include klystrons, magnetrons, and backward-wave oscillators; solid-state generators include tunnel diodes, Gunn diodes, IMPATT diodes,transistor oscillators, masers, and harmonic generators using varactor diodes. The vacuum-tubegenerators are used to produce higher powers, which can be as much as thousands ofkilowatts. Solid-state generators were formerly limited in power to a few watts, but their powercapabilities are continually increasing and now may reach hundreds of watts.
A radio signal in the frequency range from 1 to 40 GHz or from 1 to 300 GHz, depending on therating system. Numerous transmission systems use microwaves including line-of-sight betweenbuildings and across vast distances, as well as communications satellites, cellular systems andwireless LANs. Early Microwave TowerLine-of-sight microwaves were first used to transmit across long distances where the terrain wastoo difficult to lay cable. This tower was installed in 1969 in Boulder Junction, Colorado. (Imagecourtesy of AT&T.)
APPLICATIONSAreas in which microwave radiation is applied include radar, communications, radiometry,medicine, physics, chemistry, and cooking food.Radar is used in military applications, commercial aviation, remote sensing of the atmosphere,and astronomy. The high antenna directivity and the excellent propagation characteristics ofmicrowaves in the atmosphere make this the preferred band for radar applications. Microwavesare also used in electronic countermeasures to radar. See also Electronic warfare; Radar.There is at least 100 times as much frequency space available for communications in themicrowave band as in the entire spectrum below microwaves. In addition, the high directivityobtainable at microwave frequencies allows reuse of these frequencies many times in the samearea, a practice not possible at lower frequencies. The high directivity also makes possiblecommunication to satellites and deep-space probes. See also Radio spectrum allocations;Space communications.All objects, including liquids and gases, emit electromagnetic radiation in the form of noise, theamount of the noise being proportional to the absolute temperature of the object. A noisetemperature can be assigned to the object corresponding to the amount of noise radiating fromit. A microwave radiometer is a sensitive receiver which measures the noise power received byan antenna; from this measurement, the noise temperature of the source object can bedetermined. Radiometers are used extensively for remote sensing. Microwave radiometers areused to study astronomical sources of noise and to observe planets from deep space probes.See also Passive radar; Radiometry; Remote sensing.Applications of microwaves in medicine include (1) thermography, the measurement of tissuetemperature; (2) hyperthermia, microwave heating used in the treatment of cancer and in thetreatment of hypothermic subjects; and (3) biomedical imaging, the use of microwaves to studythe structure of tissue beneath the skin. See also Radiology.Physics and chemistryMicrowave energy is used in large particle accelerators to accelerate charged particles such aselectrons and protons to very high energies and cause them to collide. Knowledge of thestructure of matter is also obtained from microwave spectroscopy. See also Microwavespectroscopy; Particle accelerator.Microwave energy is absorbed in most foods and has been found to be a source of quick,uniform heating or cooking. Microwave ovens based upon this principle are now widely used.Microwaves are also used for the industrial heating of foodstuffs and other materials.
MICROWAVE TRANSMISSIONMicrowave transmission refers to the technology of transmitting information or power by the useof radio waves whose wavelengths are conveniently measured in small numbers of centimeters;these are called microwaves. This part of the radio spectrum ranges across frequencies ofroughly 1.0 gigahertz (GHz) to 30 GHz. These correspond to wavelengths from 30 centimetersdown to 1.0 cm.Microwaves are widely used for point-to-point communications because their small wavelengthallows conveniently-sized antennas to direct them in narrow beams, which can be pointeddirectly at the receiving antenna. This allows nearby microwave equipment to use the samefrequencies without interfering with each other, as lower frequency radio waves do. Anotheradvantage is that the high frequency of microwaves gives the microwave band a very largeinformation-carrying capacity; the microwave band has a bandwidth 30 times that of all the restof the radio spectrum below it. A disadvantage is that microwaves are limited to line of sightpropagation; they cannot pass around hills or mountains as lower frequency radio waves can.Microwave radio transmission is commonly used in point-to-point communication systems onthe surface of the Earth, in satellite communications, and in deep space radio communications.Other parts of the microwave radio band are used for radars, radio navigation systems, sensorsystems, and radio astronomy.The next higher part of the radio electromagnetic spectrum, where the frequencies are above30 GHz and below 100 GHz, are called "millimeter waves" because their wavelengths areconveniently measured in millimeters, and their wavelengths range from 10 mm down to3.0 mm. Radio waves in this band are usually strongly attenuated by the Earthly atmosphereand particles contained in it, especially during wet weather. Also, in wide band of frequenciesaround 60 GHz, the radio waves are strongly attenuated by molecular oxygen in theatmosphere. The electronic technologies needed in the millimeter wave band are also muchmore difficult to utilize than those of the microwave 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, aparabolic antenna is usually used. This is an antennathat uses a parabolic reflector to direct the microwaves.To achieve narrow beamwidths, the reflector must bemuch larger than the wavelength of the radio waves.The relatively short wavelength of microwaves allowsreasonably sized dishes to exhibit the desired highlydirectional response for both receiving andtransmitting.
MICROWAVE POWER TRANSMISSIONMicrowave power transmission (MPT) is the use of microwaves to transmit power through outerspace or the atmosphere without the need for wires. It is a sub-type of the more generalwireless energy transfer methods.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 the fact thatthey are used in microwave ovens. While high power microwaves can be painful and dangerousas in the United States Militarys Active Denial System, MPT systems are generally proposed tohave only low intensity at the rectenna.Though this would be extremely safe as the power levels would be about equal to the leakagefrom a microwave oven, and only slightly more than a cell phone, the relatively diffusemicrowave beam necessitates a large rectenna area for a significant amount of energy to betransmitted.Research has involved exposing multiple generations of animals to microwave radiation of thisor higher intensity, and no health issues have been foundProposed usesMPT is the most commonly proposed method for transferring energy to the surface of the Earthfrom solar power satellites or other in-orbit power sources. MPT is occasionally proposed for thepower supply in [beam-powered propulsion] for orbital lift space ships. Even though lasers aremore commonly proposed, their low efficiency in light generation and reception has led somedesigners to opt for microwave based systems.Current statusWireless Power Transmission (using microwaves) is well proven. Experiments in the tens ofkilowatts have been performed at Goldstone in California in 1975 and more recently (1997) atGrand Bassin on Reunion Island. In 2008 a long range transmission experiment successfullytransmitted 20 watts 92 miles (148 km) from a mountain on Maui to the main island of Hawaii
MICROWAVE RADIO RELAYMicrowave radio relay is a technology for transmitting digital and analog signals, such as long-distance telephone calls and the relay of television programs to transmitters, between twolocations on a line of sight radio path. In microwave radio relay, radio waves are transmittedbetween the two locations with directional antennas, forming a fixed radio connection betweenthe two points. Long daisy-chained series of such links form transcontinental telephone and/ortelevision communication systems.How microwave radio relay links are formedBecause a line of sight radio link is made, the radio frequencies used occupy only a narrow pathbetween stations (with the exception of a certain radius of each station). Antennas used musthave a high directive effect; these antennas are installed in elevated locations such as largeradio towers in order to be able to transmit across long distances. Typical types of antenna usedin radio relay link installations are parabolic reflectors, shell antennas and horn radiators, whichhave a diameter of up to 4 meters. Highly directive antennas permit an economical use of theavailable frequency spectrum, despite long transmission distances.Planning considerationsBecause of the high frequencies used, a quasi-optical line of sight between the stations isgenerally required. Additionally, in order to form the line of sight connection between the twostations, the first Fresnel zone must be free from obstacles so the radio waves can propagateacross a nearly uninterrupted path. Obstacles in the signal field cause unwanted attenuation,and are as a result only acceptable in exceptional cases. High mountain peak or ridge positionsare often ideal: Europes highest radio relay station, the Richtfunkstation Jungfraujoch, issituated atop the Jungfraujoch ridge at an altitude of 3,705 meters (12,156 ft) above sea level.Obstacles, the curvature of the Earth, the geography of the area and reception issues arisingfrom the use of nearby land (such as in manufacturing and forestry) are important issues toconsider when planning radio links. In the planning process, it is essential that "path profiles"are produced, which provide information about the terrain and Fresnel zones affecting thetransmission path. The presence of a water surface, such as a lake or river, in the mid-pathregion also must be taken into consideration as it can result in a near-perfect reflection (evenmodulated 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 asmall spot and a narrow frequency band, so space and/or frequency diversity schemes wouldbe applied to mitigate these effects.The effects of atmospheric stratification cause the radio path to bend downward in a typicalsituation so a major distance is possible as the earth equivalent curvature increases from6370 km to about 8500 km (a 4/3 equivalent radius effect). Rare events of temperature,humidity and pressure profile versus height, may produce large deviations and distortion of thepropagation and affect transmission quality. High intensity rain and snow must also beconsidered as an impairment factor, especially at frequencies above 10 GHz. All previousfactors, collectively known as path loss, make it necessary to compute suitable power margins,in order to maintain the link operative for a high percentage of time, like the standard 99.99% or99.999% used in carrier class services of most telecommunication operators. [[File:TV remote
pickup Pier 88 jeh.JPG|thumb|left|Portable microwave rig for Electronic news gathering (ENG)for television newsOver-horizon microwave radio relayIn over-horizon, or tropospheric scatter, microwave radio relay, unlike a standard microwaveradio relay link, the sending and receiving antennas do not use a line of sight transmission path.Instead, the stray signal transmission, known as "tropo - scatter" or simply "scatter," from thesent signal is picked up by the receiving station. Signal clarity obtained by this method dependson the weather and other factors, and as a result a high level of technical difficulty is involved inthe creation of a reliable over horizon radio relay link. Over horizon radio relay links aretherefore only used where standard radio relay links are unsuitable (for example, in providing amicrowave link to an island).USAGE OF MICROWAVE RADIO RELAY SYSTEMSDuring the 1950s the AT&T Communications system of microwave radio grew to carry themajority of US Long Distance telephone traffic, as well as intercontinental television networksignals. The prototype was called TDX and was tested with a connection between New YorkCity and Murray Hill, the location of Bell Laboratories in 1946. The TDX system was set upbetween New York and Boston in 1947. The TDX was improved to the TD2, which still usedklystrons, and then later to the TD3 that used solid state electronics. The main motivation in1946 to use microwave radio instead of cable was that a large capacity could be installedquickly and at less cost. It was expected at that time that the annual operating costs formicrowave radio would be greater than for cable. There were two main reasons that a largecapacity had to be introduced suddenly: Pent up demand for long distance telephone service,because of the hiatus during the war years, and the new medium of television, which neededmore bandwidth than radio.Similar systems were soon built in many countries, until the 1980s when the technology lost itsshare of fixed operation to newer technologies such as fiber-optic cable and optical radio relaylinks, both of which offer larger data capacities at lower cost per bit. Communication satellites,which are also microwave radio relays, better retained their market share, especially fortelevision.At the turn of the century, microwave radio relay systems are being used increasingly inportable radio applications. The technology is particularly suited to this application because oflower operating costs, a more efficient infrastructure, and provision of direct hardware access tothe 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 canbe from just a few feet or meters to several miles or kilometers apart. Microwave links arecommonly used by television broadcasters to transmit programmes across a country, forinstance, or from an outside broadcast back to a studio.
Mobile units can be camera mounted, allowing cameras the freedom to move around withouttrailing cables. These are often seen on the touchlines of sports fields on Steadicam 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 communications