Two Cavity Klystron Amplifier: Construction, Operation, and HF Tube Limitations

hello and welcome you all dear students today's topic is two cavity KRON amplifier before uh discussing this

working and construction of a two cavity Clon amplifier first let us discuss the high frequency HF means high frequency

high frequency limitations of the conventional tubes from the exam point of view you may expect the question like

this what are high frequency limitations of the conventional tubes and how these liit itations can be overcome or can be

minimized so first limitation is lead inductance and Inter electrode capacitance effect there are different

electrodes between which the capacitance is created as well as the leads are present so it it produces certain effect

that is the lead inductance effect as the frequency increases we know that microwave is having a very high

frequency so as the frequency increases especially if frequency becomes more than 1 GHz then the capacitance between

the electrodes of a vacuum tube and the lead inductance of a wire goes on increasing this upward Arrow indicates

values goes on increasing in case of high frequencies the real part of input admittance re

means real part real part of the input admittance is very very large so the operating frequency of the tube goes on

reducing it affects the performance of a tube remedy uh to this problem to this limitation is reduce the lead length as

well as reduce the electrode area so it will reduce down the effect of lead inductance and Inter electrode

capacitance second limitation is Transit time effect Transit time is the time taken by the electrons uh to move from

cathode to anode the transit time is doned by notation to it is given by D by V 0 where small D is the distance

between anode and cathode V 0 is the velocity of electrons at micro frequency this Transit time is large so electrons

can ulate back and forth and it may happen that some of the electrons May return back to the cathode So to avoid

this or to minimize this effect accelerate Electron Beam with a high DC voltage and it should be followed by the

voltage by the velocity modulation process third limitation is gain bandwidth product the gain bandwidth is

having a fixed value at the higher frequencies that is at the uh micro frequencies and particularly at the

resonance condition the gain of device is increased but gain is increased and gain bandwidth product is fixed so it

will reduceed on the bandwidth of the device so So to avoid such limitations to minimize this limitation use

re-entrant cavities or you may use slow W structure it will reduce down the uh speed so fourth limitation is RF losses

radio frequency losses at the higher frequencies the current which is flowing through the circuit is confined to a

very small cross-sectional area so as the frequency increases this type of losses RF losses goes on

increasing this can be avoided by increasing the size of the conductor fifth type of limitation is dialectric

losses we know that uh different types of insulating materials are used for example glass envelopes are used which

causes dialectric losses so to reduce down uh this dialectric loss effect or this limitation reduce the surface area

of the glass and last type of limitation is radiation losses whenever the dimensions of a wire approaches towards

wavelength Lambda then the radiation starts that means the wire starts emitting the radiation it will affect

the performance of the uh circuit as well as it will reduce down the efficiency to avoid radiation losses

there should be a proper sing so this is about the high frequency limitations of the conventional tube and how to

minimize this effect So to avoid all these limitations we are going to make use of some microwave tubes

next part is classification of micro tubes the broad classification is there are two types of micro tubes one is

cross filled tubes it is also called M type tubes and another is linear beam tubes which is also called O type tubes

in case of Cross Field or M type tubes as the name indicates the fields are crossed that means in this case the DC

magnetic field and DC electric field are perpendicular to each other as well as the motion of electrons is also

perpendicular to both these things that is both to both DC magnetic and DC electric field so three things DC

electric field DC magnetic field and the motion of electrons are mutually perpendicular to each other so it is

called Crossfield microwave tubes examples are magnetron or Crossfield devices second type is linear beam tube

or O type of tube in this case the DC magnetic field is in parallel with DC electric field and the Electron Beam is

aligned with both these fields examples are KRON then twt that is traveling W tubes and so on as such we are going to

study all these devices uh in detail in this unit next part is two cavity Clon

amplifier let us first discuss the construction of two cavity Clon amplifier from the exam point of view

you may expect the like this draw the constructional details of two cavi Clon amplifier and explain its operation so

this diagram shows the construction of two cavity Chron amplifier as the name indicates there are two cavities one at

the input side this is called input cavity or buncher cavity second cavity is at the output side it is output

cavity or it is also called catcher cavity now this this part shows the cathode

which is used to emit the Electron Beam the focusing electrodes are placed on both sides of this cathode which are

used to focus the beam of electrons which is generated by the cathode now this part is the part of the

glass tube at the output side collector is shown more positive voltage is applied to the collector end now the gap

of input cavity is denoted by X and gap of output cavity is denoted by y the gap between the two cavities is called Drift

space in between these two cavities the different electron bunches are created now the RF input voltage is applied at

this point I mean is applied at the input cavity which is shown in this diagram now let us discuss the operation

of this two cavity Clon amplifier as I said the cathode is used to emit the Electron

Beam the drift space is gap between input and output cavities initially uh whenever input is

not applied basically this RF input is applied at the input cavity that is Bucher

cavity this input is to be Amplified now if RF input is not applied then look at this initial lines actually if each line

is having certain slope this line represents distance between X and Y this is X at the output cavity we have

written y so distance between them uh is called the drift space so each L represents the distance between X and Y

if initially RF input signal is not applied then observe these initial lines the slope remains constant there is no

change in the slope of these lines now consider one electron B see this is the voltage vform this electron B can be

treated as a reference electron this electron B is transferred whenever the voltage is slightly positive so because

of this the slope of the line gets changed as I said consider this as a reference electron now consider one more

electron that is electron C electron B is passed through the cavity after that electron C enters because electron C is

having more positive voltage compared to electron B since the volage of electron C is more than that of B the

acceleration of electron C takes place compared to electron B so slope of the line this line corresponding to or

compared to the line of related to electron B will be different will be changed that means make it more

simper whenever the voltage is high compared to the voltage at electron voltage of electron B so acceleration of

this electron takes place compared to the motion of electron B consider one more electron a which is passed when the

voltage is negative for this electron the acceleration will be minimum because

this electron is at the negative cycle negative half cycle so there is a difference between

the acceleration provided to each electron depending on the position of the input or position of the voltage at

which these electrons are passing through the Gap so the point is that certain electrons are traveling with

high speed certain electrons are traveling with low speed this electron a was transmitted earlier before passing

of el Elon B and C the acceleration of electron B is more than a acceleration of electron C is more than b as well as

more than a so it may happen that in between this Gap in the drift space the uh slower electrons will be captured

will be catched by the faster electron so different bunches are created this is called the bunching process so these

different bunches are shown in this diagram now all these bunches are formed due to the fast and slow motion of the

corresponding electrons whenever the bunches are formed faster electrons transfer energy to the slower electron

and all these bunches are captured in the output cavity that is catcher cavity and from this point the output is

generated so this is how the amplification process takes place basically amplification takes place due

to the formation of different bunches or due to the bunching process so this is about the working of two cavity Clon

amplifier now let us solve a numerical given question is two cavity Clon amplifier has following characteristics

voltage gain which is given in DB it is 10 DB input power 5 mwatt shun resist impedance of input cavity that is rsh of

input cavity is 30 kilo then same CH impedance of output cavity 40 kilm total output impedance the notations can

notation can be r0 or RN so it is 40 Kil determine input voltage second part output voltage third part power deliver

to the load I have written the corresponding formula so first is input power is expressed as V in square that

is square of input voltage upon rsh for input power for at input side so this is at input side now we are supposed to

calculate input voltage initially so from this formula I can write v² is = p in into rsh of the input side now input

power is given as 5 m so it is 5 m means 5 into 10us 3 given value is in m so I have converted it into WS into rsh at

input side so rsh of input cavity is 30 30 kilm so it is 30 into 10 3 so you'll get value of v in square but

actually we need V in so take square root of this term this 10us 3 10 + 3 gets cancelled so square root of 150

will give you answer 12247 volt this is the answer of first part now for the second part we have the

formula of voltage gain 20 log V upon v0 upon V in do remember the voltage gain is given in DB so the corresponding

equation is 20 log of this ratio now let us put the values so in this equation a that is voltage gain is this value is

given in the question which is 10 DB so I can write 10 is = 20 log of v0 upon just now we have calculated value of V

that is 12247 so I can write it like this log of v0 upon

12247 is equal to 10 by 20 that is equals to.5 therefore v0 upon

12247 is anti log of5 therefore v0 is equals to I will

transfer this 12247 at the rhs side so it becomes 12247 into 10 to.5 because it is anti-log so answer of v0 is

38728 volt this is the answer of second part that is the answer of output voltage now third part power deliver to

the load we have SIMPLE formula V 0 squ upon RL the notation can be RL or r0 so PL I will get it as v0 squ that is

this value 38.78 squ upon RL 40 K that is 40 into 10 3 so this gives me the value of out

power deliver to the load which is .375 wat you may well convert it in mwatts that will be 37.5 M so this is

the way how to solve the uh for two cavity clone amplifier so dear students that's it for today's

session so thank you thanks a lot for watching this video