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lar to the helical twt however instead of the rf signal propagating in the same or similar direction as the electron beam the original signal travels at right angles to the beam this is normally accomplished by drilling a hole through a rectangular waveguide and shooting the beam through the hole the waveguide then goes through two right angle turns forming a c shape and crossing the beam again this basic pattern is repeated along the length of the tube so the waveguide passes across the beam several times forming a series of s shapes 2 the original rf signal enters from what would be the far end of the twt where the energy would be extracted the effect of the signal on the passing beam causes the same velocity modulation effect but because of the direction of the rf signal and specifics of the waveguide this modulation travels backward along the beam instead of forward this propagation the slow wave reaches the next hole in the folded waveguide just as the same phase of the rf signal does this causes amplification just like the traditional twt 2 in a traditional twt the speed of propagation of the signal in the induction system has to be similar to that of the electrons in the beam this is required so that the phase of the signal lines up with the bunched electrons as they pass the inductors this places limits on the selection of wavelengths the device can amplify based on the physical construction of the wires or resonant chambers 2 this is not the case in the bwo where the electrons pass the signal at right angles and their speed of propagation is independent of that of the input signal the complex serpentine waveguide places strict limits on the bandwidth of the input signal such that a standing wave is formed within the guide but the velocity of the electrons is limited only by the allowable voltages applied to the electron gun which can be easily and rapidly changed thus the bwo takes a single input frequency and produces a wide range of output frequencies 2 carcinotron edit this image shows the effect of four carcinotron carrying aircraft on a typical 1950s pulse radar the aircraft are located at roughly the 10 00 and 11 30 locations the display is filled with noise any time the antenna s main lobe or sidelobes pass the jammer rendering the aircraft invisible the device was originally given the name carcinotron after the greek name for the crayfish which swim backwards 4 by simply changing the supply voltage the device could produce any required frequency across a band that was much larger than any existing microwave amplifier could match the cavity magnetron worked at a single frequency defined by the physical dimensions of their resonators and while the klystron amplified an external signal it only did so efficiently within a small range of frequencies 2 previously jamming a radar was a complex and time consuming operation operators had to listen for potential frequencies being used set up one of a bank of amplifiers on that frequency and then begin broadcasting when the radar station realized what was happening they would change their frequencies and the process would begin again in contrast the carcinotron could sweep through all the possible frequencies so rapidly that it appeared to be a constant signal on all of the frequencies at once typical designs could generate hundreds or low thousands of watts so at any one frequency there might be a few watts of power that is received by the radar station however at long range the amount of energy from the original radar broadcast that reaches the aircraft is only a few watts at most so the carcinotron can overpower them 2 the system was so powerful that it was found that a carcinotron operating on an aircraft would begin to be effective even before it rose above the radar horizon as it swept through the frequencies it would broadcast on the radar s operating frequency at what were effectively random times filling the display with random dots any time the antenna was pointed near it perhaps 3 degrees on either side of the target there were so many dots that the display simply filled with white noise in that area as it approached the station the signal would also begin to appear in the antenna s sidelobes creating further areas that were blanked out by noise at close range on the order of 100 miles 160 km the entire radar display would be completely filled with noise rendering it useless 2 the concept was so powerful as a jammer that there were serious concerns that ground based radars were obsolete airborne radars had the advantage that they could approach the aircraft carrying the jammer and eventually the huge output from their transmitter would burn through the jamming however interceptors of the era relied on ground direction to get into range using ground based radars this represented an enormous threat to air defense operations 5 for ground radars the threat was eventually solved in two ways the first was that radars were upgraded to operate on many different frequencies and switch among them randomly from pulse to pulse a concept now known as frequency agility some of these frequencies were never used in peacetime and highly secret with the hope that they would not be known to the jammer in wartime the carcinotron could still sweep through the entire band but then it would be broadcasting on the same frequency as the radar only at random times reducing its effectiveness the other solution was to add passive receivers that triangulated on the carcinotron broadcasts allowing the ground stations to produce accurate tracking information on the location of the jammer and allowing them to be attacked 5 the slow wave structure edit a forward fundamental space harmonic n 0 b backward fundamental the needed slow wave structures must support a radio frequency rf electric field with a longitudinal component the structures are periodic in the direction of the beam and behave like microwave filters with passbands and stopbands due to the periodicity of the geometry the fields are identical from cell to cell except for a constant phase shift φ this phase shift a purely real number in a passband of a lossless structure varies with frequency according to floquet s theorem see floquet theory the rf electric field e z t can be described at an angular frequency ω by a sum of an infinity of spatial or space harmonics e n e z t n e n e j ω t k n z displaystyle e z t sum _ n infty infty e_ n e j omega t k_ n z where the wave number or propagation constant k n of each harmonic is expressed as k n φ 2nπ p π φ π z being the direction of propagation p the pitch of the circuit and n an integer two examples of slow wave circuit characteristics are shown in the ω k or brillouin diagram on figure a the fundamental n 0 is a forward space harmonic the phase velocity v n ω k n has the same sign as the group velocity v g dω dk n synchronism condition for backward interaction is at point b intersection of the line of slope v e the beam velocity with the first backward n 1 space harmonic on figure b the fundamental n 0 is backward a periodic structure can support both forward and backward space harmonics which are not modes of the field and cannot exist independently even if a beam can be coupled to only one of them as the magnitude of the space harmonics decreases rapidly when the value of n is large the interaction can be significant only with the fundamental or the first space harmonic m type bwo edit schematic of an m bwo the m type carcinotron or m type backward wave oscillator uses crossed static electric field e and magnetic field b similar to the magnetron for focussing an electron sheet beam drifting perpendicularly to e and b along a slow wave circuit with a velocity e b strong interaction occurs when the phase velocity of one space harmonic of the wave is equal to the electron velocity both e z and e y components of the rf field are involved in the interaction e y parallel to the static e field electrons which are in a decelerating e z electric field of the slow wave lose the potential energy they have in the static electric field e and reach the circuit the sole electrode is more negative than the cathode in order to avoid collecting those electrons having gained energy while interacting with the slow wave space harmonic o type bwo edit the o type carcinotron or o type backward wave oscillator uses an electron beam longitudinally focused by a magnetic field and a slow wave circuit interacting with the beam a collector collects the beam at the end of the tube o bwo spectral purity and noise edit the bwo is a voltage tunable oscillator whose voltage tuning rate is directly related to the propagation characteristics of the circuit the oscillation starts at a frequency where the wave propagating on the circuit is synchronous with the slow space charge wave of the beam inherently the bwo is more sensitive than other oscillators to external fluctuations nevertheless its ability to be phase or frequency locked has been demonstrated leading to successful operation as a heterodyne local oscillator frequency stability edit the frequency voltage sensitivity is given by the relation δ displaystyle delta f f 1 2 1 1 v φ v g δ displaystyle delta v 0 v 0 the oscillation frequency is also sensitive to the beam current called frequency pushing the current fluctuations at low frequencies are mainly due to the anode voltage supply and the sensitivity to the anode voltage is given by δ displaystyle delta f f 3 4 ω q ω 1 v φ v g δ displaystyle delta v a v a this sensitivity as compared to the cathode voltage sensitivity is reduced by the ratio ω q ω where ω q is the angular plasma frequency this ratio is of the order of a few times 10 2 noise edit measurements on submillimeter wave bwo s de graauw et al 1978 have shown that a signal to noise ratio of 120 db per mhz could be expected in this wavelength range in heterodyne detection using a bwo as a local oscillator this figure corresponds to a noise temperature added by the oscillator of only 1000 3000 k notes edit fr patent 1035379 bernard epsztein backward flow travelling wave devices published 1959 03 31 1 2 3 4 5 6 7 8 9 10 microwave principles us navy september 1998 p 103 gilmour a s 2011 klystrons traveling wave tubes magnetrons crossed field amplifiers and gyrotrons artech house pp 317 18 isbn 978 1608071852 minenna damien f g andré frédéric elskens yves auboin jean françois doveil fabrice puech jérôme duverdier élise 2019 01 16 the traveling wave tube in the history of telecommunication european physical journal h 44 1 1 36 arxiv 1803 11497 bibcode 2019epjh 44 1m doi 10 1140 epjh e2018 90023 1 1 2 morris alec 1996 uk control reporting system from the end of wwii to rotor and beyond in hunter sandy ed defending northern skies royal air force historical society pp 105 106 references edit johnson h r 1955 backward wave oscillators proceedings of the ire 43 6 684 697 ramo s whinnery j r van duzer t fields and waves in communication electronics 3rd ed 1994 john wiley sons kantorowicz g palluel p backward wave oscillators in infrared and millimeter waves vol 1 chap 4 k button ed academic press 1979 de graauw th anderegg m fitton b bonnefoy r gustincic j j 3rd int conf submm waves guilford university of surrey 1978 convert g yeou t in millimeter and submillimeter waves chap 4 1964 illife books london external links edit wikimedia commons has media related to backward wave oscillator virtual valve museum thomson csf cv6124 wayback machine v t e electronic components semiconductor devices mos transistors transistor nmos pmos bicmos biofet chemical field effect transistor chemfet complementary mos cmos depletion load nmos fin field effect transistor finfet floating gate mosfet fgmos insulated gate bipolar transistor igbt isfet ldmos mos field effect transistor mosfet multi gate field effect transistor mugfet power mosfet thin film transistor tft vmos umos qfet tunnel field effect transistor tfet high electron mobility transistor hemt rf cmos native transistor other transistors bipolar junction transistor bjt darlington transistor diffused junction transistor field effect transistor fet junction gate fet jfet organic fet ofet light emitting transistor let pentode transistor point contact transistor programmable unijunction transistor put static induction transistor sit tetrode transistor nanoscale vacuum channel transistor nvct single electron transistor set heterojunction bipolar transistor hbt mesfet heterostructure emitter bipolar transistor hebt itfet avalanche transistor junctionless nanowire transistor jlnt schottky transistor spin transistor ballistic collection transistor ballistic deflection transistor bdt drift field transistor organic electrochemical transistor oect spacistor surface barrier transistor synaptic transistor oxide thin film transistor nomfet grown junction transistor eosfet alloy junction transistor fe fet dna field effect transistor dnafet diodes avalanche diode shockley diode selenium rectifier fast diode single photon avalanche diode spad constant current diode cld crd gunn diode varicap impatt diode metal insulator metal diode mim diode transient voltage suppression diode tvs diode laser diode ld light emitting diode led organic light emitting diode oled photodiode pin diode p n diode tunnel diode avalanche photodiode apd solar cell multi junction solar cell mj hybrid solar cell schottky junction solar cell plasmonic solar cell heterojunction solar cell hjt schottky diode step recovery diode srd zener diode resonant tunneling diode rtd photoreflector backward diode geometric diode lr diode chua s diode baritt diode stabistor phosphorescent organic light emitting diode pholed thin film diode superluminescent diode sld josephson diode hole accumulation diode had silicon photomultiplier sipm metal rectifier bifacial solar cells bsc integrated circuits hybrid integrated circuit hic mixed signal integrated circuit mos integrated circuit mos ic three dimensional integrated circuit 3d ic photonic integrated circuit pic application specific integrated circuit asic field programmable gate array fpga system on a chip soc other devices diac heterostructure barrier varactor light emitting capacitor lec memistor memristor memtransistor memory cell metal oxide varistor mov organic semiconductor photodetector silicon controlled rectifier scr silicon controlled switch scs solaristor static induction thyristor sith thyristor trancitor triac varicap vertical cavity surface emitting laser vcsel gate turn off thyristor gto integrated gate commutated thyristor igct unijunction transistor ujt quantum cascade laser qcl photoresistor quantum dot display quantum dot solar cell photoelectrochemical cell dye sensitized solar cell plasmonic solar cell quantum dot laser quadrac interband cascade laser icl oscillistor mos composite static induction thyristor csmt mos controlled thyristor mct resistive opto isolator ro emitter turn off thyristor eto...