NATIONAL COLLEGE OF SCIENCE AND TECHNOLOGY Amafel Bldg. Aguinaldo Highway Dasmariñas City, Cavite ASSIGNMENT # 2 Microwave Technology Agdon, Berverlyn B. October 03, 2011 Communications 1/ BSECE 41A1 Score:_________ Engr. Grace Ramones Instructor
MicrowaveThe term microwave refers to electromagnetic energy having a frequency higher than1 gigahertz (billions of cycles per second), corresponding to wavelength shorter than 30centimeters.Microwave signals propagate in straight lines and are affected very little by thetroposphere. They are not refracted or reflected by ionized regions in the upperatmosphere. Microwave beams do not readily diffract around barriers such as hills,mountains, and large human-made structures. Some attenuation occurs whenmicrowave energy passes through trees and frame houses. Radio-frequency (RF)energy at longer wavelengths is affected to a lesser degree by such obstacles.The microwave band is well suited for wireless transmission of signals having largebandwidth. This portion of the RF electromagnetic radiation spectrum encompassesmany thousands of megahertz. Compare this with the so-called shortwave band thatextends from 3 MHz to 30 MHz, and whose total available bandwidth is only 27 MHz. Incommunications, a large allowable bandwidth translates into high data speed. Theshort wavelengths allow the use of dish antennas having manageable diameters. Theseantennas produce high power gain in transmitting applications, and have excellentsensitivity and directional characteristics for reception of signals.
Microwave transmission refers to the technology of transmitting information orpower by the use of radio waves whose wavelengths are convenientlymeasured in small numbers of centimeters; these are called microwaves. Thispart of the radio spectrum ranges across frequencies of roughly 1.0 gigahertz(GHz) to 30 GHz. These correspond to wavelengths from 30 centimeters down to1.0 cm.Microwaves are widely used for point-to-point communications because theirsmall wavelength allows conveniently-sized antennas to direct them in narrowbeams, which can be pointed directly at the receiving antenna. This allowsnearby microwave equipment to use the same frequencies without interferingwith each other, as lower frequency radio waves do. Another advantage is thatthe high frequency of microwaves gives the microwave band a very largeinformation-carrying capacity; the microwave band has a bandwidth 30 timesthat of all the rest of the radio spectrum below it. A disadvantage is thatmicrowaves are limited to line of sight propagation; they cannot pass aroundhills or mountains as lower frequency radio waves can.Microwave radio transmission is commonly used in point-to-pointcommunication systems on the surface of the Earth, in satellite communications,and in deep space radio communications. Other parts of the microwave radioband are used for radars, radio navigation systems, sensor systems, and radioastronomy.The next higher part of the radio electromagnetic spectrum, where thefrequencies are above 30 GHz and below 100 GHz, are called "millimeter waves"because their wavelengths are conveniently measured in millimeters, and theirwavelengths range from 10 mm down to 3.0 mm. Radio waves in this band areusually strongly attenuated by the Earthly atmosphere and particles containedin it, especially during wet weather. Also, in wide band of frequencies around60 GHz, the radio waves are strongly attenuated by molecular oxygen in theatmosphere. 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 thatuses a parabolic reflector to direct the microwaves. To achieve narrowbeamwidths, the reflector must be much larger than the wavelength of theradio waves. The relatively short wavelength of microwaves allows reasonablysized dishes to exhibit the desired highly directional response for both receivingand transmitting.
Microwave sourcesVacuum tube devices operate on the ballistic motion of electrons in a vacuum underthe influence of controlling electric or magnetic fields, and include the magnetron,klystron, traveling-wave tube (TWT), and gyrotron. These devices work in the densitymodulated mode, rather than the current modulated mode. This means that they workon the basis of clumps of electrons flying ballistically through them, rather than using acontinuous stream.Low power microwave sources use solid-state devices such as the field-effect transistor(at least at lower frequencies), tunnel diodes, Gunn diodes, and IMPATT diodes.A maser is a device similar to a laser, which amplifies light energy by stimulatingphotons. The maser, rather than amplifying light energy, amplifies the lower frequency,longer wavelength microwaves and radio frequency emissions.The sun also emits microwave radiation, and most of it is blocked by Earthsatmosphere.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 tenradio channels combined into one antenna for the hop to the next site, up to 70 kmaway.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) WirelessInternet Access services have been used for almost a decade in many countries in the3.5–4.0 GHz range. The FCC recently[when?] carved out spectrum for carriers that wish tooffer services in this range in the U.S. — with emphasis on 3.65 GHz. Dozens of serviceproviders across the country are securing or have already received licenses from theFCC to operate in this band. The WIMAX service offerings that can be carried on the3.65 GHz band will give business customers 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 tooperate between 2 to 11 GHz. Commercial implementations are in the 2.3 GHz,2.5 GHz, 3.5 GHz and 5.8 GHz ranges.Mobile Broadband Wireless Access (MBWA) protocols based on standardsspecifications such as IEEE 802.20 or ATIS/ANSI HC-SDMA (such as iBurst) operatebetween 1.6 and 2.3 GHz to give mobility and in-building penetration characteristicssimilar to mobile phones 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-DMB use 1.452 to 1.492 GHz, while proprietary/incompatible satellite radio in the U.S.uses around 2.3 GHz for DARS.Microwave radio is used in broadcasting and telecommunication transmissionsbecause, due to their short wavelength, highly directional antennas are smaller andtherefore more practical than they would be at longer wavelengths (lowerfrequencies). There is also more bandwidth in the microwave spectrum than in the restof the radio spectrum; the usable bandwidth below 300 MHz is less than 300 MHz whilemany GHz can be used above 300 MHz. Typically, microwaves are used in televisionnews to transmit a signal from a remote location to a television station from a speciallyequipped van. See broadcast auxiliary service (BAS), remote pickup unit (RPU), andstudio/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 characteristicsof remote objects. Development of radar was accelerated during World War II due toits great military utility. Now radar is widely used for applications such as air trafficcontrol, weather forecasting, navigation of ships, and speed limit enforcement.A Gunn diode oscillator and waveguide are used as a motion detector for automaticdoor openers.Radio astronomyMost radio astronomy uses microwaves. Usually the naturally-occurring microwaveradiation is observed, but active radar experiments have also been done with objectsin the solar system, such as determining the distance to the Moon or mapping theinvisible surface of Venus through cloud cover.NavigationGlobal Navigation Satellite Systems (GNSS) including the Chinese Beidou, the AmericanGlobal Positioning System (GPS) and the Russian GLONASS broadcast navigationalsignals in 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 thewater, fats, and sugar contained in the food. Microwave ovens became commonkitchen appliances in Western countries in the late 1970s, following development ofinexpensive cavity magnetrons. Water in the liquid state possesses many molecularinteractions which broaden the absorption peak. In the vapor phase, isolated watermolecules absorb at around 22 GHz, almost ten times the frequency of the microwaveoven.Microwave heating is used in industrial processes for drying and curing products.Many semiconductor processing techniques use microwaves to generate plasma forsuch purposes as reactive ion etching and plasma-enhanced chemical vapordeposition (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
plasma state. The upcoming ITER Thermonuclear Reactoris expected to range from110–170 GHz and 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 1980sto research 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 ofhuman skin to an intolerable temperature so as to make the targeted person moveaway. A two-second burst of the 95 GHz focused beam heats the skin to a temperatureof 130 °F (54 °C) at a depth of 1/64th of an inch (0.4 mm). The United States Air Forceand Marines are currently 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.