magnetron_theory-operation_and_design .pdf

magnetron operation and design

1. UNIT-III (PART A)
MICROWAVE TUBES
Basic operating principle of microwave tube is
to produce the power required for maximum
frequency
LIMITATIONS OF CONVENTIONAL TUBES AT
MICROWAVE FREQUENCIES: -
1.Effects of inter electrode capacitance
2.Effect due to lead inductance
3.Effect due to transit time
4.Limitations of gain bandwidth product

2. EFFECTS OF INTER ELECTRODE CAPACITANCE 1
2
c
c
X
f

OPERATION:-
As fc increases,
Xc decreases,
voltage deceases,
power decreases
Distance between plates
decreases,
Short circuit occurs
Circuit may damage
REMEDY:-
To increase the plate distance


A= area of the electrode
d= distance between electrode
= free space permittivity
= relative permittivity 0r
A
C
d

 0
 r


3. EFFECT DUE TO LEAD INDUCTANCE 2
LL
Xf
OPERATION:-
As fL increases,
XL increases,
gain deceases,
bandwidth decreases
REMEDY:-
To decrease XL



A= area of the electrode
l= length of the coil
= free space permeability
= relative permeability 0r
l
L
A
 0
 r


4. EFFECT DUE TO TRANSIT TIME
The time required for the electrons to travel from cathode to anode plate is
called transit time(Ʈ)

5. LIMITATIONS OF GAIN BANDWIDTH PRODUCT
OPERATION:-
Maximum gain is achieved at a
particular frequency
As frequency increases,
gain deceases,
bandwidth decreases
REMEDY:-
To use RE-ENTRANT CAVITY
Which produces maximum gain at
larger frequencies m
m
g
AXBW
C
 m
A
= maximum voltage gain at resonance
BW= bandwidth
= trans conductance
C=the capacitance of the tank circuit m
g

6. LOSSES OF CONVENTIONAL TUBES
AT MICROWAVE FREQUENCIES: -

•SKIN EFFECT LOSSES OR CONDUCTOR LOSSES
OR I2R LOSSES
•DIELECTRIC LOSSES
•RADIATION LOSSES

7. CLASSIFICATION OF MICROWAVE TUBES

8. RE-ENTRANT CAVITIES

9. COAXIAL CAVITY RADIAL CAVITY

10. •Used to produce high frequencies by
reducing inductance & capacitance values
•Easily incorporated into microwave device
structures
•Easily couples and take out the signal
from these devices
•Commonly used re-entrant cavity is
coaxial cavity
• re-entrant cavity reduces inductance
losses, resistance losses and radiation
losses
RE-ENTRANT CAVITIES / IRREGULAR-SHAPED
RESONATORS

11. LINEAR BEAM (O TYPE) TUBES
SCHEMATIC DIAGRAM OF A GENERIC LINEAR BEAM TUBE

12. TYPES OF LINEAR BEAM (O TYPE)
TUBES
(1)One type of tube uses electromagnetic cavities
(2)Other type of tube uses slow-wave structure
Both types of tubes uses electron beam

OPERATION:-
Electrons from cathode posses kinetic energy interacts with electron
beam and RF input interacts with electron beam and both gets converted
in microwave energy. At the RF output this microwave energy is
extracted by using re-entrant cavity which is present in electron beam
and remaining portion of electron beam is dissipated in the form of heat
to the collector. Magnetic fields are used to propagate the electrons into
electron beam from cathode with out any reflections.

13. 2 CAVITY KLYSTRON AMPLIFIER

14. INTERNAL STRUCTURE OF 2 CAVITY KLYSTRON AMPLIFIER

15. •Consists of 2 cavities
–One is buncher cavity :-produces RF i/p signal which is
to be amplified
–Another is Cather cavity:- produces RF amplified o/p
signal
•VDC provides 300v energy to electron beam and emits
electrons by potential energy
•At GAP A electrons from cathode interacts with RF i/p
signal and form a bunch
•One bunch consists of one complete cycle
•Remaining electrons which consists of low frequency
will be dissipated from collector

OPERATION OF 2 CAVITY KLYSTRON
AMPLIFIER

16. APPLE GATE DIAGRAM OF 2 CAVITY
KLYSTRON(operation at drift space)
r
e-reference
electron
l
e-late
electron
e
e- earlier
electron

17. •DC BEAM VOLTAGE (Vdc upto 300v)
•DRIFT SPACE (SPACE BETWEEN GAP A & GAP
B)
•SIGNAL AMPLITUDE
PARAMETERS IN APPLE GATE

18. REFLEX KLYSTRON
•It is a single cavity klystron
•It provides variable frequency (4GHZ-
200GHZ)
•Generates low power(1mW-2.5mW) and low
efficiency (22.78%)
•Maximum theoretical efficiency ranges from
20% to 30%

19. STRUCTURE OF REFLEX KLYSTRON

20. OPERATION OF REFLEX KLYSTRON
•It consists of an electron gun, anode cavity (RF
output) and a repeller.
•It uses only a single re-entrants microwave
cavity as resonator. The electron beam
emitted from the electron gun(-ve charge)
which passes to the repeller space(-ve charge)
, repelles back and attract to the anode cavity
(+ve charge), form a bunch of electrons and
comes out as a output

22. SCHEMATIC DIAGRAM OF SIMPLE
REFLEX KLYSTRON

23. APPLEGATE DIAGRAM OF REFLEX
KLYSTRON
T=n+3/4

24. OSCILLATING MODES AND OUTPUT
CHARACTERISTICS OF REFLEX KLYSTRON
T=n+3/4
Where n is any integer that depends on repeller voltage & anode voltage

25. EFFECT OF REPELLER VOLTAGE ON POWER
OUTPUT

26. INTRODUCTION
•TWTs represents Travelling Wave Tubes
•It is nonresonant circuit
•Wave will propagate in helical line
•It is a slow wave structure
•It provides high output
•It has very long life period
•It consists of high gain of about 40dB, with low
noise , high power and high bandwidth.
•Its frequency range is about 300MHz-50GHz

27. TYPES OF SLOW WAVE
STRUCTURES
HELICAL LINE FOLDED BACK LINE ZIGZAG LINE
INTER DIGITAL LINE CORRUGATED WAVE GUIDE

28. HELICAL LINE
•It is the most commonly
used slow wave structure
•It consists of a thin
ribbon of metal that is
wound into a helical
structure
•It is constructed with a
round wire that act as a
slow wave structure

29. DIAGRAM FOR HELICAL STRUCTURE 
•The diagram is
very useful in designing
a helix slow-wave
structure.


30. DIAGRAM FOR SPACIAL HARMONICS
OF A HELICAL STRUCTURE 

31. SCHEMATIC DIAGRAM OF A TRAVELLING-
WAVE-TUBE

32. AMPLIFICATION PROCESS

33. INTRODUCTION
•M represents magnetic, which deals with the
propagation of electric field and magnetic
field in cylindrical wave guide.
•Both electric field and magnetic field are
perpendicular to each other

34. M-TYPE TUBES
CROSSED-FIELD TUBES
LINEAR BEAM TUBES

35. OUTER VIEW OF CYLINDRICAL
MAGNETRON

36. 8-CAVITY CYLINDRICAL
MAGNETRON
STRUCTURE OF A CAVITY
MAGNETRON
CYLINDRICAL
CONFIGURATION
MAGNETIC FIELD

37. ELECTRON TRAJECTORIES AT
VARIOUS MAGNETIC FIELDS
NO MAGNETIC FIELD
MAGNETIC FIELD =Bc
SMALL MAGNETIC FIELD
MAGNETIC FIELD > Bc

38. MODES OF RESONANCE &
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39. HARTREE CONDITION

40. STRAPPING OF MAGNETRONS