magnetron_theory-operation_and_design .pdf
- 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 0 r A C d 0 r
- 3. EFFECT DUE TO LEAD INDUCTANCE 2 L L X f 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 0 r 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 A XBW 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
- 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) re-reference electron le-late electron ee- 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
- 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 & 𝝅 𝑴𝑶𝑫𝑬 𝑶𝑷𝑬𝑹𝑨𝑻𝑰𝑶𝑵