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Mwoc Unit 2

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Mwoc Unit 2

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muskan s
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(Magnetron Oscillator) Microwave Tubes {-! ne Linear Beam Tubes (Ordinary type) 0-Type Cross-Field Tubes (Magnetic Type) (M- Type) yh Magnetron ¥ CFA Y y Y j Klystron TWT Twystrons Carcinotrong (Cross field Amplifier) | ss ' ' Helix Backwardwave Couple Ring bar Oscillator (BWO) Cavity Ring loop Two cavity Klystron Multicavity Klystron Reflex Klystron Amplifier Amplifier Oscillator Mechanism _of_ oscillations in Magnetron- The magnetron requires an external magnetic field with flux lines parallel to the axis of cathode. This field is provided by a permanent magnet or electromagnet. The dc magnetic field is normal to the dc electric field between the cathode and anode. Because of the cross-field between the cathode and anode, the electrons emitted from the cathode are affected by the cross-field to move in curved paths. 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Document Nome: (©2017 Xeox Copeation Al Rh Rese ‘rou, Xara ond Das ore Pacemaster Crpsieton nthe Unted States anor thes counties SAS Wea’ Trek AL mode d_ eran com eect Yb AN As Gx el anmmees Ag RN trew y= Pew wrod pp filoronun ef called Oh AR- Mode - N= 6 trow Py=o THM ph called U the zero mode Zeca there will fo no RF Elecbut fee afur te awh amd Oe codhrat . ws alboCalley as frimging fcUp Ong Thin ede tb wet ped “im op Cowd ' ‘ele iy tage coal , bse Mat ipl shes te oof + Can le fir thaw bee idk op oleclrwd, Ca oan fle pve 9 . e Wh OW Gary NE LRG) Go chindly zack @ puoi sued ahha Aerox WOrKLENLE 3655 XeLOXx © Workflow Scanning Confirmation Report _» Job Details: Job Status: Cae oh 0 out of 1 filed successfully. ee ob Infomation Destin: Sts rausD Catan wwoacs ues 0630 Sansa coat Sarena tomo Sams Te oso Fenton Deft tk Fon Maine Sewn Tangles tomato ae pm Prot oom Fanaa Aino Due Doar Name Fle Settings ra Ioge-OnFOF Destin 2 usin atone Seneoeo onesie ° Frenne Bytes led: ° ‘ServerName: am Scam Setngs Prt capone o rahe. Croat tine Prato Tt Dramer Ne vowhodsed Peter Orpratreton Peat Oss Orgrelsar ode Dentin 3 Becki Pasig Siren on Sausbeate Uspeenater Nal Fredy const ea one supe Nema mae Saunton nema Protect Sato Set roar. reawen yeoss Dearne DieprPt x Onna ‘tobe Outyriesee Patera Desinion sous Cres ne AER MULT Sensors Fredy Nae ioonine ne Peek fanaa Doom Destin: Soon Sousa frente ert rate Peet Fargo Boaee Nan Detain sa Sensei fren Name sport ae ei fanaa. Dramer None 0 opin. pth Xerox, Xerox and Oesign af derma of Xerox Copan nthe Unted Sates andl other outs. 10/22/21, 4:25 PM Microwave Engineering - Magnetrons Microwave Engineering - Magnetrons Unlike the tubes discussed so far, Magnetrons are the cross-field tubes in which the electric and magnetic fields cross, i.e. run perpendicular to each other. In TWT, it was observed that electrons when made to interact with RF, for a longer time, than in Klystron, resulted in higher efficiency. The same technique is followed in Magnetrons. wee ih a dnie a Types of Magnetrons There are three main types of Magnetrons fede nike ope of ok ver Tegnche , cited A Negative Resistance Type Covbilibed ob tA ee pane * The negative resistance between two anade segments, is used a cyoted ~feeld + They have low efficiency. + They are used at low frequencies < 500M Hz Cyclotron Frequency Magnetrons + The synchronism between the electric component and oscillating electrons is considered + Useful for frequencies higher than 100MHz. Travelling Wave or Cavity Type + The interaction between electrons and rotating EM ficid is taken into account + High peak power oscillations are provided. + Useful in radar applications Cavity Magnetron The Magnetron is called as Cavity Magnetron because the anode is made into resonant cavities and a permanent magnet is used to produce a strong magnetic field, where the action of both of these make the device work. Construction of Cavity Magnetron A thick cylindrical cathode is present at the center and a cylindrical block of copper, is fixed axially, which acts as an anode. This anode block is made of a number of slots that acts as resonant anode cavities. https wu tutorialspoint conmicrowave_engineering/microwave_engineering_magnetrons him 16 10722721, 425 PM Microwave Engineering - Magnetrons The space present between the anode and cathode is called as Interaction space. The electric field is present radially while the magnetic field is present axially in the cavity magnetron. This magnetic field is produced by a permanent magnet, which is placed such that the magnetic lines are parallel to cathode and perpendicular to the electric field present between the anode and the cathode. The following figures show the constructional details of a cavity magnetron and the magnetic lines of flux present, axially Q >. Ir “Ss 5 Construction details of » Cavity Magnetron Magnetic flux lines in Magnetron (axial) pP BB NY A This Cavity Magnetron has 8 cavities tightly coupled to each other. An N-cavity magnetron has NN modes of operations. These operations depend upon the frequency and the phase of oscillations. The total phase shift around the ring of this cavity resonators should be 2nm where n_ is an integer. If dy represents the relative phase change of the AC electric field across adjacent cavities, then 2m N Ss Where n=0, +1, +2, + (4-1), + wz Which means that mode of resonance can exist if N is an even number. lz https: tutoralspoint corv/microwave_engineeringimicrowave_engineering_magnetrons him tomar, 425 crave Engeerng-Magnovons TR uff router n=X then d= Ef ope os [rroctivce Lcftesund frre Tor adjuamb arcade (ai tromme o phate ifpens n=0 then $y =0 TK hada This mode of resonance is called as 7 — mode and Calle of Ma woods This is called as the Zero mode, because there will be no RF electric field between the anode and the cathode. This is also called as Fringing Field and this mode is not used in magnetrons. Operation of Cavity Magnetron When the Cavity Klystron is under operation, we have different cases to consider. Let us go through them in detail. Case 1 If the magnetic field is absent, i.e. B = 0, then the behavior of electrons can be observed in the following figure. Considering an example, where electron a directly goes to anode under radial electric force ‘Anode block Interaction space Cathode no magne! field is present Case 2 If there is an increase in the magnetic field, a lateral force acts on the electrons. This can be observed in the following figure, considering electron b which takes a curved path, while both forces are acting on it hitps:/immwtutoralspoint.com/microwave_ongineering/microwave_engineering_magnetrons htm 36 sate / war an Movement of electron b when small magnetic field is present Radius of this path is calculated as mv R-B It varies proportionally with the velocity of the electron and it is inversely proportional to the magnetic field strength. Case 3 If the magnetic field B is further increased, the electron follows a path such as the electron c, just grazing the anode surface and making the anode current zero. This is called as "Critical magnetic ich is the cut-off magnetic field. Refer the following figure for better field” (B.) , wi understanding. ‘Anode block space Cathode Movement of electron ¢ when the magnetic field is critical magnetic fieldie. B= Be Case 4 tps: tutorialspoint com/microwave_engineering/microwave_engineering_magnetrons.htm 10122/21, 425 PM ‘Microwave Engineering - Magnetions If the magnetic field is made greater than the critical field, B>B, Then the electrons follow a path as electron d, where the electron jumps back to the cathode, without going to the anode. This causes "back heating" of the cathode. Refer the following figure. Anode block Interaction space Cathode Movement of electron d when excessive magnetic field is present This is achieved by cutting off the electric supply once the oscillation begins. If this is continued, the ‘emitting efficiency of the cathode gets affected Operation of Cavity Magnetron with Active RF Field We have discussed so far the operation of cavity magnetron where the RF field is absent in the cavities of the magnetron staticcase . Let us now discuss its operation when we have an active RF field, As in TWT, let us assume that initial RF oscillations are present, due to some noise transient. The oscillations are sustained by the operation of the device. There are three kinds of electrons emitted in this process, whose actions are understood as electrons a, b and ¢, in three different cases. Case 1 Wren oscillations are present, an electron a, slows down transferring energy to oscillate. Such electrons that transfer their energy to the oscillations are called as favored electrons. These electrons are responsible for bunching effect. Case 2 In this case, another electron, say b, takes energy from the Oscillations and increases its velocity. As and when this is done, tps / ww tutorilepoint com/microwave_engineeringimicrowave_engineering_magnetrons hm L4 1072221, 425 PM Microwave Engineering - Magnetrons + Itbends more sharply. + It spends little time in interaction space + Itreturns to the cathode. These electrons are called as unfavored electrons. They don't participate in the bunching effect. Also, these electrons are harmful as they cause "back heating" Case 3 In this case, electron ¢, which is emitted a little later, moves faster. It tries to catch up with electron a. The next emitted electron d, tries to step with a. As a result, the favored electrons a, ¢ and d form electron bunches or electron clouds. It called as "Phase focusing effect” This whole process is understood better by taking a look at the following figure. Figure A shows the electron movements in different cases while figure B shows the electron clouds. formed. These electron clouds occur while the device is in operation. The charges present on the internal surface of these anode segments, follow the oscillations in the cavities. This creates an electric field rotating clockwise, which can be actually seen while performing a practical experiment. While the electric field is rotating, the magnetic flux lines are formed in parallel to the cathode, under whose combined effect, the electron bunches are formed with four spokes, directed in regular intervals, to the nearest positive anode segment, in spiral trajectories. Per aks [Paled noes) 19900 (OME b Powers OfP > In exces End) Gk Cat EMS) ere fuenuy 2 ate (eG ‘ety eye 2 0-117 Ye SET, Ped He gh mt Dnt op ond & mibaak 2 te oe & ao are Aa AS itl oe § Le 8e ake o i sniapmaguthon Bs The mest comm w (2 common parallel pals % thd Crobigield a = Bev vs Db giver bq : l hee Vj oh, Ene ai Aime : - > lM Zz ALE: o a aa rts ae — Yee ee Tp = PF cape tit antl =. a? lee crore Ae > d[agxme’] © febhoele qinsiie Taeape Cade. 1S a “hie: e-p-bp:B es amp dh mF ab é. ) ‘ C0998. 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Baked 07 taaba'condtouction . « Pycwt condo dO : : ' Scholthy darrne* + metal onrdo abst) deve etal imblalion Aces - above bold Make ee Frome row ae Wp PI wedulal ot dn comin yp Comrie 1 Oscillations e Let the cavity magnetron has 8 cavities, by which it supports varieties of modes depending upon the phase difference between fields in two adjacent cavities. Boundary conditions are satisfied when total phase shift around the eight cavities is multiplied by 27 radians. However, the most important mode for magnetron operation is one where in the phase shift between the fields of adjacent cavities is m radians. This is known as 2-Mode. Hull cut- off voltage & Hartee condition In a cylindrical magnetron, several re-entrant cavities are connected to the gaps. Thus it is also called as Cavity Magnetron. Assume the radius of cathode is ‘a’ and anode is ‘b’. The dc voltage V)is applied between the cathode and anode. When the dc voltage and the magnetic flux (i.e. which is in the +ve z-direction) are adjusted properly, the electrons will follow parabolic path in the presence of cross field. These parabolic paths are formed in the cathode-anode space under the combined force of both electric and magnetic fields which are perpendicular to each other. quejsuod Bulje/3ajU! = 9 pue 7/21 = 4'(3p/4P4)/ ‘QJ0UM (ur + (2/ed@9) = (esu)x(3p/p) <= A, 44 Muolenba anoge BuljeiZa}uU! 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G & these ” peer anee Re wiser thot Selpete, gnake a dod exhibit tor p ry 06 Pevalanchetraubst tine, At hate ace IM PAT? 2) TRAPATT 3) BreltT: Th prouss ep having a dulay go precise ef bf Vottag ImpatT Diode — — Tonio Prvalonht © qmpart (® Abode bh aw ext used b tee tit cel he ATT ed ag fe deal att > yeu b ot fal bee ur the trams tis cont ET impact: we teualcow ee tpsaiht leew ep INATT “lt Le two tyr: ) cimgle Ag 2) Dokl dbf OU LL DIATE Ay Uwe INGE it NEN ntper. ponon. we comkdt tke PY Nt Lovie, Te pry junction jh Connceted nr houerseoumd Pham ie COMMAAN oNalauckedreok haru Th ranks The tage 7 Pt te igech into N NF bythe a Lecbuhaldo velo- antl Pen né drift region er —>!2um |3um'4—— 104m (400kv/em) IMPATT diode schematic “dS 5 alee 2 anid 100-8 thes Wighs — Tae primespte } cyjahantte breakedam a —banit pve Abi ea roa, 10:52 AM Avalanche Transit Tane Devices Due to this effect, the current pulse takes a phase shift of 90°. However, instead of being there, it moves towards cathode due to the reverse bias applied. The time taken for the pulse to reach cathode depends upon the thickness of n+ layer, which is adjusted to make it 90° phase shift. Now, a dynamic RF negative resistance is proved to exist. Hence, IMPATT diode acts both as an oscillator and an amplifier. The following figure shows the constructional details of an IMPATT diode. Cu cathode z Je seal Gold wire Ne 0 Gold wire Pe 23mm hi erer ic Gold alloy =e contact < Cuanode Constructional details of IMPATT The efficiency of IMPATT diode is represented as Where, + Pye = AC power + Pye =DC power . V, & I, = AC voltage & current . Va & Ig = DC voltage & current Disadvantages Following are the disadvantages of IMPATT diode. https Aww tutorialspoint com/microwave_engineering/microwave_engineering_avalanche_transit_time_devices.htm a a 10/29/21, 10:52 AM ‘Avalanche Transit Time Devices It is noisy as avalanche is a noisy process Tuning range is not as good as in Gunn diodes Applications Following are the applications of IMPATT diode. . Microwave oscillator . Microwave generators + Modulated output oscillator . Receiver local oscillator 8 + Negative resistance amplifications + Intrusion alarm networks highQIM PATT + Police radar highQIM PATT + Low power microwave transmitter highQIM PATT + FMtelecom transmitter lowQIM PATT * CWDoppler radar transmitter lowQIM PATT TRAPATT Diode The full form of TRAPATT diode is TRApped Plasma Avalanche Triggered Transit diode. A microwave generator which operates between hundreds of MHz to GHz. These are high peak power diodes usually n+- p-p+ or p+-n-n+ structures with n-type depletion region, width varying from 2.5 to 1.25 Aum. The following figure depicts this. :ngineeting/microwave_engineering_avalanche_tansittime_devices. htm 39 10123,21, 10:52 AM Avalanche Transit Time Devices: Square wave current drive F 50m for cw & 750 um for low frequency ¥_ high peak power . 25t012.5 um depletion layer Arrangement in TRAPATT diode The electrons and holes trapped in low field region behind the zone, are made to fill the depletion region in the diode. This is done by a high field avalanche region which propagates through the diode. The following figure shows a graph in which AB shows charging, BC shows plasma formation, DE shows plasma extraction, EF shows residual extraction, and FG shows charging Let us see what happens at each of the points. A: The voltage at point A is not sufficient for the avalanche breakdown to occur. At A, charge carriers due to thermal generation results in charging of the diode like a linear capacitance. A-B: At this point, the magnitude of the electric field increases. When a sufficient number of carriers are generated, the electric field is depressed throughout the depletion region causing the voltage to decrease from B to C. C: This charge helps the avalanche to continue and a dense plasma of electrons and holes is created. The field is further depressed so as not to let the electrons or holes out of the depletion layer, and traps the remaining plasma tps: ww tutorialspoint com/microwave_engineering/microwave_engineering_avalanche_transit_time_devices.htm \ EE 1072921, 1052 AM ‘valonche Transit Tine Devices D: The voltage decreases at point D. A long time is required to clear the plasma as the total plasma charge is large compared to the charge per unit time in the external current E: At point E, the plasma is removed. Residual charges of holes and electrons remain each at ‘one end of the deflection layer. E to F: The voltage increases as the residual charge is removed. F: At point F, all the charge generated internally is removed. F to G: The diode charges like a capacitor. G: At point G, the diode current comes to zero for half a period. The voltage remains constant as shown in the graph above. This state continues until the current comes back on and the cycle repeats. The avalanche zone velocity V, is represented as de J 4-2 -— dt @Na Where + J = Current density . q = Electron charge 1.6 x 10°'9 + N4_ = Doping concentration The avalanche zone will quickly sweep across most of the diode and the transit time of the carriers is represented as Where V,_ = Saturated carrier drift velocity . L = Length of the specimen ‘tips wv tutorialspoint com/microwave_engineeringimicrowave_engineering_avalanche_transittime_devices.him 1012921, 10:52AM ‘Avalanche Transit Time Devices The transit time calculated here is the time between the injection and the collection. The repeated action increases the output to make it an amplifier, whereas a microwave low pass filter connected in shunt with the circuit can make it work as an oscillator. Applications There are many applications of this diode. * Low power Doppler radars + Local oscillator for radars + Microwave beacon landing system + Radio altimeter * Phased array radar, etc. BARITT Diode The full form of BARITT Diode is BARrier Injection Transit Time diode. These are the latest invention in this family. Though these diodes have long drift regions like IMPATT diodes, the carrier injection in BARITT diodes is caused by forward biased junctions, but not from the plasma of an avalanche region as in them In IMPATT diodes, the carrier injection is quite noisy due to the impact ionization. In BARITT diodes, to avoid the noise, carrier injection is provided by punch through of the depletion region The negative resistance in a BARITT diode is obtained on account of the drift of the injected holes to the collector end of the diode, made of p-type material The following figure shows the constructional details of a BARITT diode. ites! wiv tutorialspoint commicrowave_engineering/microwave_engineeting_avalanche_transittime_devices.htm a9 10729721, 10:52 AM Avalanche Transit Time Devices (3 * ntype c (Si wafer) , Drift region e } Electric — + Distance Construction of BARITT diode For a2 m-n-m BARITT diode, Ps-Si Schottky barrier contacts metals with n-type Si wafer in between. A rapid increase in current with applied voltage above30v_ is due to the thermionic hole injection into the semiconductor. The critical voltage (Vc) depends on the doping constant (N) , length of the semiconductor (L) and the semiconductor dielectric permittivity (€S) represented as qNL? 2eS Monolithic Microwave Integrated Circuit MMIC Microwave ICs are the best alternative to conventional waveguide or coaxial circuits, as they are low in weight, small in size, highly reliable and reproducible. The basic materials used for monolithic microwave integrated circuits are ~ + Substrate material + Conductor material https tutorialepoint.com/microwave_engineering/mictowave_engineering_avalanche. transit time_devices.htm 719 102321, 1052 AM * Dielectric films + Resistive films These are so chosen to have ideal characteristics and high efficiency. The substrate on which circuit elements are fabricated is important as the dielectric constant of the material should be high with low dissipation factor, along with other ideal characteristics. The substrate materials used are GaAs, Ferrite/gamet, Aluminum, beryllium, glass and rutile. The conductor material is so chosen to have high conductivity, low temperature coefficient of resistance, good adhesion to substrate and etching, etc. Aluminum, copper, gold, and silver are mainly used as conductor materials. The dielectric materials and resistive materials are so chosen to have low loss and good stability. Fabrication Technology In hybrid integrated circuits, the semiconductor devices and passive circuit elements are formed on a dielectric substrate. The passive circuits are either distributed or lumped elements, or a combination of both. Hybrid integrated circuits are of two types + Hybrid Ic + Miniature Hybrid IC In both the above processes, Hybrid IC uses the distributed circuit elements that are fabricated on IC using a single layer metaliization technique, whereas Miniature hybrid IC uses multi-level elements. Most analog circuits use meso-isolation technology to isolate active n-type areas used for FETs and diodes. Planar circuits are fabricated by implanting ions into semi-insulating substrate, and to provide isolation the areas are masked off. “Via hole” technology is used to connect the source with source electrodes connected to the ground, in a GaAs FET, which is shown in the following figure. https wm tuterialspoint com/microwave_engineering/microwave_engineering_avalanche_transittime_devices.htmn 10/29/21, 10:52 AM Avalanche Transit Time Devices contact layer Drain Source Drain —n channel layer ~ Buffer layer Semi insulating substrate Plated gold via hole connection Via-hole technology in monolithic IC’s There are many applications of MMICs + Military communication + Radar ECM Phased array antenna systems Spread spectrum and TDMA systems They are cost-effective and also used in many domestic consumer applications such as DTH, telecom and instrumentation, etc. BARITT Dota v- , Limilaralies figs Sacer cae fee tr ARITT Aire used @ ly Me sinaley we and 10 Us fa Gaks LAS Gly 1 Si ae Tipfawhac EARP AieH dc Qiete pe Tho te Baviett Arete USE L Hgiwentt. emildion ralkor thie avalan nelly reat) . > Brkiticicde Car provebuee Laws serie nnerpfl hail FAA BUMER evens meme tg = oh - Se Bho (PONE 8 apps WE of ALAS JTC ALM the, parse be Atode . > a4, tke Voltage MAtww Morreked witdl Kh chyes oy the ciphtiow hago met Ka a Condition Kmown a punchy troup oc FT =e feel Aiute 4s athe dye ofthe u ens pe oe thos te the io ar ee 7 z Colo ASS WAN gy vues So = TRL hackword Nove pedialh (B08) is Alow Wore — and alts en tte winuple M eelrlation 34 pee. 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