ECE4312_Lecture 01_2024_Summer course.pdf

What is RF?
RF = Radio frequency
Used as shorthand for
Alternating voltages at radio frequencies
Alternating currents at radio frequencies
Electromagnetic waves at radio frequencies
Power carried in electromagnetic waves
Apparatus generating RF power
What are radio frequencies?
Long waves~200 kHz
Medium waves~1 MHz
Short waves~3–30 MHz
VHF radio~100 MHz
TV~500 MHz
Mobile phones~1000–2000 MHz
Satellite TV~10000 MHz
Accelerators~1 MHz –10000 MHz
http://www.ofcom.org.uk/static/archive/ra/publication/ra_info/ra365.htm#table
Wavelengths and frequencies?
c= lf
Velocity = wavelength ×frequency
Velocity of light= 3×108metres/second
= 186,000 miles/second
= 670,000,000 miles/hour
= 300 m/μs
Alternating voltages, currents, electric fields, magnetic fields, ...
Need to describe by three quantities
Frequency, amplitude and phase
E.g. three-phase AC mains:
All phases “240 V”
But different phases are very different!
Phase varies along a wire carrying alternating current
How much phase changes depends on wavelength and hence on frequency

1. Lecture 01: Introduction to RF
ECE 4312: RF Circuit Design
6/7/2024 DR. ENG. MOHAMED ISMAIL 1

2. DR. ENG. MOHAMED ISMAIL 2
Course
Grading
method Score %
Quizzes 5
Lab performance 7
Midterm exam 18
Final exam 70
Total 100

3. 3
What is RF?
RF = Radio frequency
Used as shorthand for
Alternating voltages at radio frequencies
Alternating currents at radio frequencies
Electromagnetic waves at radio frequencies
Power carried in electromagnetic waves
Apparatus generating RF power
...

4. 4
What are radio frequencies?
Long waves ~200 kHz
Medium waves~1 MHz
Short waves~3–30 MHz
VHF radio ~100 MHz
TV ~500 MHz
Mobile phones~1000–2000 MHz
Satellite TV~10000 MHz
Accelerators~1 MHz –10000 MHz
http://www.ofcom.org.uk/static/archive/ra/publication/ra_info/ra365.htm#table

5. 5
Wavelengths and frequencies?
c= lf
Velocity = wavelength ×frequency

6. 6
Wavelengths and frequencies?
c= lf
Velocity = wavelength ×frequency
Velocity of light= 3×10
8
metres/second
= 186,000 miles/second
= 670,000,000 miles/hour
= 300 m/µs

7. 7

8. 8
Frequencies Wavelengths
Long waves ~200 kHz ~1500 m
Medium waves~1 MHz ~300 m
Short waves~3–30 MHz ~10–100 m
VHF radio ~100 MHz ~3 m
TV ~500 MHz ~2 feet
Mobile phones~1000–2000 MHz~6–12 inches
Satellite TV~10000 MHz ~1 inch
Accelerators~1 MHz –10000 MHz
240 VAC mains50 Hz ~4000 miles

9. 9
Relative size
matters

10. BBC Droitwich transmitter —Long wave Radio 4

11. Marconi’s transmitter, 1902 —Nova Scotia

12. Marconi’s spark transmitter, 1910

13. Steam engine and alternator

14. Two of four 5 kV DC generators

15. 12 kV stand-by battery (6000 cells! 2 GJ stored energy!)
(cf.RAL SC3: 5 J)

16. Marconi’s 1920 valve transmitter

17. 17
Alternating voltages, currents, electric fields,
magnetic fields, ...
Need to describe by three quantities
Frequency, amplitude and phase
E.g. three-phase AC mains:
All phases “240 V”
But different phases are very different!
Phase varies along a wire carrying alternating current
How much phase changes depends on wavelength and
hence on frequency

18. 18y = sin (2 f t + )
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
0 90 180 270 360 450 540 630 720 810 900 990 1080
Degrees
Amplitude
Alternating voltage V(t) = A sin (2pf t + f)
f= 240°120°0°
E.g.three-phase AC mains
Phase

19. 19
Why is RF used at all in accelerators?
Cathode ray tube in TV set doesn’t need RF

20. 20
Particles accelerated using electric field
For 100 keV can use 100 kV DC power supply
unit. Even 665 kV for old Cockcroft-Walton
But 800,000,000 V DC power supply unit for
accelerating protons in ISIS not possible
Instead, for high energies, use RF fields, and
pass particles repeatedly through these fields
RF fields produce bunchedbeams
DC
RF
ns –µs spacing

21. 21
Air
Sound waves
set up inside
milk bottle
RF
Electromagnetic
waves set up
inside hollow
metal cylinder

22. 22
RF

23. 23
+–+ –+ –+ –+ –
RF

24. 24

25. 25
–+– +– +– +– +

26. 26

27. 27
Two commercial
0.5 MW short
wave radio
transmitters

28. 28
RF powers
Big radio and TV transmitters0.5 MW
Mobile phone transmitters30 W
Mobile phones 1 W
Sensitivity of mobile phones10
–10
W

29. 29
Where does RF power come from?
Big amplifiers
Usually purpose built
The basics:
Accelerator
RF
amplifier
Frequency
source

30. ~1 W RF ~1 MW RF

31. 31
Devices that amplify RF
Transistors
~100 watts maximum per transistor
Couple lots together for kilowatts
Valves / vacuum tubes
Triodes, tetrodes
Largest can deliver several megawatts (peak)
Klystrons
High powers, high gains
Limited to frequencies >300 MHz
IOTs (inductive output tubes)
Often used in TV transmitters (esp. digital TV)
Output limited to ~50 kW

32. 32
Transistors usually junction transistors (NPN, PNP)
Essentially minority carrier device
But RF transistors usually field effect transistors
Majority carrier device

33. Field effect transistor

34. Typical RF MOSFET

35. Solid state RF amplifier: few watts in, 3 kW max out

36. 3 kW max. solid state amplifier mounted in rack

37. 1 kW solid state driver RF amplifier for synchrotron

38. Valves / vacuum tube made in 1915

39. Basic triode circuit
Load
Anode
power
supply
+
–
Anode
Heater
Cathode
Grid
Electrons

40. Valve-based audio hi-fi amplifiers

41. Debuncher amplifier: commercial TV transmitter

42. Linac triode
5 MW peak
75 kW mean
Synchrotron tetrode
1000 kW peak
350 kW mean

43. 43
Typical valve parameters at ISIS
TH116 4648
Type Triode Tetrode
Heater 20 V, 500 A 4 V, 1600 A
Anode volts 35 kV 16 kV
Anode current 175 A 8 A
Peak power o/p2 MW 75 kW
Mean power o/p 40 kW 40 kW
Cooling water 100 l/min 200 l/min

44. 44
Resonant circuits
Parallel LC-circuit
Impedance Z “infinite” at f= f
0
(2pf
0)²= 1 / LC
L C
length l
Shorted line
Impedance Z “infinite” at
l= l/4, 3l/4,5l/4, ...
Only ratioof diameters
matters

45. 45
Output
Input
HT (+ve)
Anode
Screen grid
Control grid
Cathode
Heater
Tetrode
Essence of a tuned RF amplifier —1

46. 46
Output
Input
HT (+ve)
Anode
Screen grid
Control grid
Cathode
Heater
Tetrode
Essence of a tuned RF amplifier —2

47. ISIS RFQ 200 kW tetrode driver
Input (grid)
tuned circuit
Output (anode)
tuned circuit
Tetrode

48. 48
Klystron gain ~50 dB
(×10
5
power gain)
E.g.10 W in, 1 MW out
IOT gain ~25 dB
(×300 power gain)
E.g.200 W in, 60 kW out

49. Toshiba E3740A 3 MW 324 MHz klystron
5 metres, 3 tons

50. 50
Skin depth
RF currents flow in surface of conductor only
Skin depth d 1  (frequency) (exponential)
In copper, d= 7 / (frequency) (cm)
50 Hz 1 cm
1 MHz 70 µm
200 MHz5 µm
In sea water
50 Hz ~100 feet ELF / submarines
10 kHz~10 feet VLF / submarines

51. ISIS RFQ —vessel copper-plated stainless steel

52. Different currents
on different
surfaces of same
piece of metal
Linac high power
RF amplifier

53. 53
– +– +– +– +
Electric field
Dielectric material
No external electric field
Atoms

54. 54
Dielectric material
Dielectric constant
Ceramic 6
Nylon 3
Perspex 3½
Polystyrene2½
Water 80
Loss tangent —leads to dielectric heating
Ceramic 0.001
Nylon 0.02
Perspex 0.01
Polystyrene0.0001
Water 0.1 —microwave ovens

55. 55
RF
amplifier
Accelerating cavity
Beam
Vacuum
Air
Air Vacuum
RF
Window

56. RF feed to linac tank

57. Window and aperture

58. Good and failed RF windows

59. Linac RF block diagram
Low
level
RF
Cavity n
RF amp. chain
Tuner

Vref. accel. field
Phase
comp.
Volt.
comp.
Phase
comp.
Motor
drive
beam
Servo systems on amplitude, phase and cavity tuning

60. Three amplifiers in
previous slide

61. Synchrotron high power RF systems

62. Synchrotron low-level RF systems block diagram
Beam
compensation
loop
Phase
loop
Voltage
loop
Frequency
sweeper
Cavity
tuning

63. Driver amplifier

64. Cavity and high power RF driver

65. High power RF drive