NATIONAL COLLEGE OF SCIENCE AND TECHNOLOGY Amafel Bldg. Aguinaldo Highway Dasmariñas City, Cavite ASSIGNMENT 2 MICROWAVE TECHNOLOGYCauan, Sarah Krystelle P. October 03, 2011Communications 1/ BSECE 41A1 Score: Engr. Grace Ramones Instructor
MICROWAVE TECHNOLOGYMicrowaves are electromagnetic waves withwavelengths ranging from as long as one meter to asshort as one millimeter, or equivalently, withfrequencies between 300 MHz (0.3 GHz) and 300 GHz.This broad definition includes both UHF and EHF(millimeter waves), and various sources use differentboundaries. In all cases, microwave includes the entireSHF band (3 to 30 GHz, or 10 to 1 cm) at minimum, withRF engineering often putting the lower boundary at1 GHz (30 cm), and the upper around 100 GHz (3mm).Apparatus and techniques may be describedqualitatively as "microwave" when the wavelengths ofsignals are roughly the same as the dimensions of theequipment, so that lumped-element circuit theory isinaccurate. As a consequence, practical microwavetechnique tends to move away from the discrete resistors, capacitors, and inductors usedwith lower frequency radio waves. Instead, distributed circuit elements and transmission-line theory are more useful methods for design and analysis. Open-wire and coaxialtransmission lines give way to waveguides and stripline, and lumped-element tunedcircuits are replaced by cavity resonators or resonant lines. Effects of reflection,polarization, scattering, diffraction and atmospheric absorption usually associated withvisible light are of practical significance in the study of microwave propagation. The sameequations of electromagnetic theory apply at all frequencies.While the name may suggest a micrometer wavelength, it is better understood as indicatingwavelengths much shorter than those used in radio broadcasting. The boundaries betweenfar infrared light, terahertz radiation, microwaves, and ultra-high-frequency radio wavesare fairly arbitrary and are used variously between different fields 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 in theso-called infrared and optical window frequency ranges.
Microwave sourcesVacuum tube devices operate on the ballistic motion of electrons in a vacuum under theinfluence of controlling electric or magnetic fields, and include the magnetron, klystron,traveling-wave tube (TWT), and gyrotron. These devices work in the density modulatedmode, rather than the current modulated mode. This means that they work on the basis ofclumps of electrons flying ballistically through them, rather than using a continuousstream.Low power microwave sources use solid-state devices such as the field-effect transistor (atleast at lower frequencies), tunnel diodes, Gunn diodes, and IMPATT diodes.A maser is a device similar to a laser, which amplifies light energy by stimulating photons.The maser, rather than amplifying light energy, amplifies the lower frequency, longerwavelength microwaves and radio frequency emissions.The sun also emits microwave radiation, and most of it is blocked by Earths atmosphere.The Cosmic Microwave Background Radiation (CMBR) is a source of microwaves thatsupports the science of cosmologys Big Bang theory of the origin of the Universe.
UsesCommunicationBefore the advent of fiber-optic transmission, most long distance telephone calls werecarried via networks of microwave radio relay links run by carriers such as AT&T LongLines. Starting in the early 1950s, frequency division multiplex was used to send up to5,400 telephone channels on each microwave radio channel, with as many as ten radiochannels 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 usemicrowaves in the 2.4 GHz ISM band, although 802.11a uses ISM band and U-NIIfrequencies in the 5 GHz range. Licensed long-range (up to about 25 km) Wireless InternetAccess services have been used for almost a decade in many countries in the 3.5–4.0 GHzrange. The FCC recently[when?] carved out spectrum for carriers that wish to offer services inthis range in the U.S. — with emphasis on 3.65 GHz. Dozens of service providers across thecountry are securing or have already received licenses from the FCC to operate in this band.The WIMAX service offerings that can be carried on the 3.65 GHz band will give businesscustomers another option for connectivity.Metropolitan area network (MAN) protocols, such as WiMAX (Worldwide Interoperabilityfor Microwave Access) are based on standards such as IEEE 802.16, designed to operatebetween 2 to 11 GHz. Commercial implementations are in the 2.3 GHz, 2.5 GHz, 3.5 GHz and5.8 GHz ranges.Mobile Broadband Wireless Access (MBWA) protocols based on standards specificationssuch as IEEE 802.20 or ATIS/ANSI HC-SDMA (such as iBurst) operate between 1.6 and2.3 GHz to give mobility and in-building penetration characteristics similar to mobilephones but with vastly greater spectral efficiency.Some mobile phone networks, like GSM, use the low-microwave/high-UHF frequenciesaround 1.8 and 1.9 GHz in the Americas and elsewhere, respectively. DVB-SH and S-DMBuse 1.452 to 1.492 GHz, while proprietary/incompatible satellite radio in the U.S. usesaround 2.3 GHz for DARS.Microwave radio is used in broadcasting and telecommunication transmissions because,due to their short wavelength, highly directional antennas are smaller and therefore morepractical than they would be at longer wavelengths (lower frequencies). There is also morebandwidth in the microwave spectrum than in the rest of the radio spectrum; the usablebandwidth below 300 MHz is less than 300 MHz while many GHz can be used above300 MHz. Typically, microwaves are used in television news to transmit a signal from aremote location to a television station from a specially equipped van. See broadcastauxiliary service (BAS), remote pickup unit (RPU), and studio/transmitter link (STL).
Most satellite communications systems operate in the C, X, Ka, or Ku bands of themicrowave spectrum. These frequencies allow large bandwidth while avoiding thecrowded UHF frequencies and staying below the atmospheric absorption of EHFfrequencies. Satellite TV either operates in the C band for the traditional large dish fixedsatellite service or Ku band for direct-broadcast satellite. Military communications runprimarily over X or Ku-band links, with Ka band being used for Milstar.RadarRadar uses microwave radiation to detect the range, speed, and other characteristics ofremote objects. Development of radar was accelerated during World War II due to its greatmilitary utility. Now radar is widely used for applications such as air traffic control,weather forecasting, navigation of ships, and speed limit enforcement.A Gunn diode oscillator and waveguide are used as a motion detector for automatic dooropeners.Radio astronomyMost radio astronomy uses microwaves. Usually the naturally-occurring microwaveradiation is observed, but active radar experiments have also been done with objects in thesolar system, such as determining the distance to the Moon or mapping the invisiblesurface of Venus through cloud cover.NavigationGlobal Navigation Satellite Systems (GNSS) including the Chinese Beidou, the AmericanGlobal Positioning System (GPS) and the Russian GLONASS broadcast navigational signalsin various bands between about 1.2 GHz and 1.6 GHz.PowerA microwave oven passes (non-ionizing) microwave radiation (at a frequency near2.45 GHz) through food, causing dielectric heating by absorption of energy in the water,fats, and sugar contained in the food. Microwave ovens became common kitchen appliancesin Western countries in the late 1970s, following development of inexpensive cavitymagnetrons. Water in the liquid state possesses many molecular interactions whichbroaden the absorption peak. In the vapor phase, isolated water molecules absorb ataround 22 GHz, almost ten times the frequency of the microwave oven.Microwave heating is used in industrial processes for drying and curing products.Many semiconductor processing techniques use microwaves to generate plasma for suchpurposes as reactive ion etching and plasma-enhanced chemical vapor deposition (PECVD).
Microwave frequencies typically ranging from 110 – 140 GHz are used in stellarators andmore notably in tokamak experimental fusion reactors to help heat the fuel into a plasmastate. The upcoming ITER Thermonuclear Reactoris expected to range from 110–170 GHzand will employ Electron Cyclotron Resonance Heating (ECRH).Microwaves can be used to transmit power over long distances, and post-World War IIresearch was done to examine possibilities. NASA worked in the 1970s and early 1980s toresearch the possibilities of using solar power satellite (SPS) systems with large solararrays that would beam power down to the Earths surface via microwaves.Less-than-lethal weaponry exists that uses millimeter waves to heat a thin layer of humanskin to an intolerable temperature so as to make the targeted person move away. A two-second burst of the 95 GHz focused beam heats the skin to a temperature of 130 °F (54 °C)at a depth of 1/64th of an inch (0.4 mm). The United States Air Force and Marines arecurrently using this type of active denial system.SpectroscopyMicrowave radiation is used in electron paramagnetic resonance (EPR or ESR)spectroscopy, typically in the X-band region (~9 GHz) in conjunction typically withmagnetic fields of 0.3 T. This technique provides information on unpaired electrons inchemical systems, such as free radicals or transition metal ions such as Cu(II). Themicrowave radiation can also be combined with electrochemistry as in microwaveenhanced electrochemistry.
Microwave frequency bandsThe microwave spectrum is usually defined as electromagnetic energy ranging fromapproximately 1 GHz to 100 GHz in frequency, but older usage includes lower frequencies.Most common applications are within the 1 to 40 GHz range. Microwave frequency bands,as defined by the Radio Society of Great Britain (RSGB), are shown in the table below:Letter Designation Frequency rangeL band 1 to 2 GHzS band 2 to 4 GHzC band 4 to 8 GHzX band 8 to 12 GHzKu band 12 to 18 GHzK band 18 to 26.5 GHzKa band 26.5 to 40 GHzQ band 33 to 50 GHzU band 40 to 60 GHzV band 50 to 75 GHzE band 60 to 90 GHzW band 75 to 110 GHzF band 90 to 140 GHzD band 110 to 170 GHz
Microwave frequency measurementMicrowave frequency can be measured by either electronic or mechanical techniques.Frequency counters or high frequency heterodyne systems can be used. Here the unknownfrequency is compared with harmonics of a known lower frequency by use of a lowfrequency generator, a harmonic generator and a mixer. Accuracy of the measurement islimited by the accuracy and stability of the reference source.Mechanical methods require a tunable resonator such as an absorption wavemeter, whichhas a known relation between a physical dimension and frequency.Wavemeter for measuring in the Ku bandIn a laboratory setting, Lecher lines can be used to directly measure the wavelength on atransmission line made of parallel wires, the frequency can then be calculated. A similartechnique is to use a slotted waveguide or slotted coaxial line to directly measure thewavelength. These devices consist of a probe introduced into the line through alongitudinal slot, so that the probe is free to travel up and down the line. Slotted lines areprimarily intended for measurement of the voltage standing wave ratio on the line.However, provided a standing wave is present, they may also be used to measure thedistance between the nodes, which is equal to half the wavelength. Precision of this methodis limited by the determination of the nodal locations.
History and researchThe existence of electromagnetic waves was predicted by James Clerk Maxwell in 1864from his equations. In 1888, Heinrich Hertz was the first to demonstrate the existence ofelectromagnetic waves by building an apparatus that produced and detected microwavesin the UHF region. The design necessarily used horse-and-buggy materials, including ahorse trough, a wrought iron point spark, Leyden jars, and a length of zinc gutter whoseparabolic cross-section worked as a reflection antenna. In 1894 J. C. Bose publiclydemonstrated radio control of a bell using millimeter wavelengths, and conducted researchinto the propagation of microwaves.Perhaps the first, documented, formal use of the term microwave occurred in 1931: "When trials with wavelengths as low as 18 cm were made known, there was undisguised surprise that the problem of the micro-wave had been solved so soon." Telegraph & Telephone Journal XVII. 179/1In 1943: the Hungarian engineer Zoltán Bay sent ultra-short radio waves to the moon,which, reflected from there worked as a radar, and could be used to measure distance, aswell as to study the moon.Perhaps the first use of the word microwave in an astronomical context occurred in 1946in an article "Microwave Radiation from the Sun and Moon" by Robert Dicke and RobertBeringer. This same article also made a showing in the New York Times issued in 1951.In the history of electromagnetic theory, significant work specifically in the area ofmicrowaves and their applications was carried out by researchers including:Specific work on microwavesWork carried out by Area of workBarkhausen and Kurz Positive grid oscillatorsHull Smooth bore magnetronVarian Brothers Velocity modulated electron beam → klystron tubeRandall and Boot Cavity magnetron
Microwave transmissionMicrowave transmission refers to the technology of transmitting information or power bythe use of radio waves whose wavelengths are conveniently measured in small numbers ofcentimeters; these are called microwaves. This part of the radio spectrum ranges acrossfrequencies of roughly 1.0 gigahertz (GHz) to 30 GHz. These correspond to wavelengthsfrom 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, which canbe pointed directly at the receiving antenna. This allows nearby microwave equipment touse the same frequencies without interfering with each other, as lower frequency radiowaves do. Another advantage is that the high frequency of microwaves gives themicrowave band a very large information-carrying capacity; the microwave band has abandwidth 30 times that of all the rest of the radio spectrum below it. A disadvantage isthat microwaves are limited to line of sight propagation; they cannot pass around hills ormountains as lower frequency radio waves can.Microwave radio transmission is commonly used in point-to-point communication systemson the surface of the Earth, in satellite communications, and in deep space radiocommunications. Other parts of the microwave radio band are used for radars, radionavigation 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 their wavelengthsare conveniently measured in millimeters, and their wavelengths range from 10 mm downto 3.0 mm. Radio waves in this band are usually strongly attenuated by the Earthlyatmosphere and particles contained in it, especially during wet weather. Also, in wide bandof frequencies around 60 GHz, the radio waves are strongly attenuated by molecularoxygen in the atmosphere. The electronic technologies needed in the millimeter wave bandare also much more 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 gridsTo direct microwaves in narrow beams for point-to-point communication links orradiolocation (radar, a parabolic antenna is usually used. This is an antenna that uses aparabolic reflector to direct the microwaves. To achieve narrow beamwidths, the reflectormust be much larger than the wavelength of the radio waves. The relatively shortwavelength of microwaves allows reasonably sized dishes to exhibit the desired highlydirectional response for both receiving and transmitting.A parabolic antenna for Erdfunkstelle Raisting, based in Raisting, Bavaria, Germany.
Microwave power transmissionMicrowave power transmission (MPT) is the use of microwaves to transmit power throughouter space or the atmosphere without the need for wires. It is a sub-type of the moregeneral 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 equipped witha combination antenna and rectifier device called a rectenna. The rectenna convertedmicrowave power into electricity, allowing the helicopter to fly. In principle, the rectennais capable of very high conversion efficiencies - over 90% in optimal circumstances.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 without havingto build cable-based infrastructure is being studied at Grand Bassin on Reunion Island inthe 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. Microwave alsoused 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 the factthat they are used in microwave ovens. While high power microwaves can be painful anddangerous as in the United States Militarys Active Denial System, MPT systems aregenerally 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 radiation ofthis or higher intensity, and no health issues have been found
Proposed usesMPT is the most commonly proposed method for transferring energy to the surface of theEarth from solar power satellites or other in-orbit power sources. MPT is occasionallyproposed for the power supply in [beam-powered propulsion] for orbital lift space ships.Even though lasers are more commonly proposed, their low efficiency in light generationand reception has led some designers to opt for microwave based systems.Microwave spyingCurrent statusWireless Power Transmission (using microwaves) is well proven. Experiments in the tensof kilowatts have been performed at Goldstone in California in 1975 and more recently(1997) at Grand Bassin on Reunion Island. In 2008 a long range transmission experimentsuccessfully transmitted 20 watts 92 miles (148 km) from a mountain on Maui to the mainisland of Hawaii
Microwave radio relayMicrowave radio relay is a technology for transmitting digital and analog signals, such aslong-distance telephone calls and the relay of television programs to transmitters, betweentwo locations on a line of sight radio path. In microwave radio relay, radio waves aretransmitted between the two locations with directional antennas, forming a fixed radioconnection between the two points. Long daisy-chained series of such links formtranscontinental telephone and/or television communication systems.How microwave radio relay links are formedRelay towers on Frazier Mountain, Southern CaliforniaBecause a line of sight radio link is made, the radio frequencies used occupy only a narrowpath between stations (with the exception of a certain radius of each station). Antennasused must have a high directive effect; these antennas are installed in elevated locationssuch as large radio towers in order to be able to transmit across long distances. Typicaltypes of antenna used in radio relay link installations are parabolic reflectors, shellantennas and horn radiators, which have a diameter of up to 4 meters. Highly directiveantennas permit an economical use of the available frequency spectrum, despite longtransmission distances.
Danish military radio relay nodePlanning 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 thetwo stations, the first Fresnel zone must be free from obstacles so the radio waves canpropagate across a nearly uninterrupted path. Obstacles in the signal field cause unwantedattenuation, and are as a result only acceptable in exceptional cases. High mountain peak orridge positions are often ideal: Europes highest radio relay station, the RichtfunkstationJungfraujoch, is situated 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 issuesto consider when planning radio links. In the planning process, it is essential that "pathprofiles" are produced, which provide information about the terrain and Fresnel zonesaffecting the transmission path. The presence of a water surface, such as a lake or river, inthe mid-path region also must be taken into consideration as it can result in a near-perfectreflection (even modulated by wave or tide motions), creating multipath distortion as thetwo received signals ("wanted" and "unwanted") swing in and out of phase. Multipathfades are usually deep only in a small spot and a narrow frequency band, so space and/orfrequency diversity schemes would be applied to 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 curvature increasesfrom 6370 km to about 8500 km (a 4/3 equivalent radius effect). Rare events oftemperature, humidity and pressure profile versus height, may produce large deviationsand distortion of the propagation and affect transmission quality. High intensity rain andsnow must also be considered as an impairment factor, especially at frequencies above10 GHz. All previous factors, collectively known as path loss, make it necessary to computesuitable power margins, in order to maintain the link operative for a high percentage oftime, like the standard 99.99% or 99.999% used in carrier class services of mosttelecommunication operators. [[File:TV remote pickup Pier 88 jeh.JPG|thumb|left|Portablemicrowave rig for Electronic news gathering (ENG) for television news
Over-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 of sighttransmission path. Instead, the stray signal transmission, known as "tropo - scatter" orsimply "scatter," from the sent signal is picked up by the receiving station. Signal clarityobtained by this method depends on the weather and other factors, and as a result a highlevel of technical difficulty is involved in the creation of a reliable over horizon radio relaylink. Over horizon radio relay links are therefore only used where standard radio relaylinks are unsuitable (for example, in providing a microwave 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 televisionnetwork signals. The prototype was called TDX and was tested with a connection betweenNew York City and Murray Hill, the location of Bell Laboratories in 1946. The TDX systemwas set up between New York and Boston in 1947. The TDX was improved to the TD2,which still used klystrons, and then later to the TD3 that used solid state electronics. Themain motivation in 1946 to use microwave radio instead of cable was that a large capacitycould be installed quickly and at less cost. It was expected at that time that the annualoperating costs for microwave radio would be greater than for cable. There were two mainreasons that a large capacity had to be introduced suddenly: Pent up demand for longdistance telephone service, because of the hiatus during the war years, and the newmedium of television, which needed more bandwidth than 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 and opticalradio 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, whichcan be from just a few feet or meters to several miles or kilometers apart. Microwave linksare commonly used by television broadcasters to transmit programmes across 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 on Steadicamsystems.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