Tracking foreign aircrafts in a designated airspace is of utmost importance for defense security. Such tracking is conventionally performed by RADARs. RADARs throw microwave radiation in all directions in an airspace and pick up signals reflected off an aircraft. But sending these picked up microwave signals, to a base station for analysis, has been a bottleneck for efficiency of these systems. This is because traditional coaxial cable links used for microwave signal transfer are noisy and susceptible to high signal loss. However, recent advances in photonics technology offer a multitude of advantages over coaxial links, like ultralow noise, wide bandwidth, low cost, immunity to electromagnetic interference, etc to name a few. Thus modern electronic warfare systems are replacing coaxial cable links with microwave photonic links for enhanced bandwidth and processing speed. This presentation will present an overview of electronic warfare, its history, principles and different strategies. Then in the next part microwave photonic links are introduced and its attractive noiseless amplification features are discussed. Then its implementation on a RADAR system are discussed.

1. Microwave Photonics in Electronic Warfare
presented by
Debanuj Chatterjee
ENS Paris-Saclay
Research Club Talk
21/02/2020

2. Contents
1 Electromagnetic Waves
2 Electronic Warfare
3 Microwave Photonics
4 Phase Sensitive Amplifiers

3. Contents
1 Electromagnetic Waves
2 Electronic Warfare
3 Microwave Photonics
4 Phase Sensitive Amplifiers

4. Electric Field Lines

5. Field Disturbance Propagation

6. Dipole Radiation

7. History of Electromagnetic Waves
Figure: James Clerk Maxwell (1831-1879).
1873 Developed theory of electromagnetism. Predicted
coupled electric and magnetic fields can travel
through vacuum as electromagnetic waves.
Predicted the speed of these waves is equal to the
speed to light.

8. History of Electromagnetic Waves
Figure: Heinrich Hertz (1857-1894).
1886 Demonstrated existence of electromagnetic waves
as predicted by Maxwell. Produced 450 MHz
waves.
1887 Showed these waves are reflected off metallic
surfaces.
1894 Died at age 36.

9. History of Electromagnetic Waves
Figure: Setup used by Hertz to produce electromagnetic waves.

10. History of Electromagnetic Waves
Figure: Jagadish Chandra Bose (1858-1937).
1894 Produced 60 GHz waves. First generation of mm
waves.

11. Electromagnetic Spectrum

12. Atmospheric Opacity

13. Doppler Effect

14. Examples of Doppler Effect
Figure: An approaching train’s sound becomes more and more shrill.

15. Examples of Doppler Effect
Figure: A bat preying by echolocation using Doppler shift of reflected
sound waves.

16. Principle of Radar

17. Contents
1 Electromagnetic Waves
2 Electronic Warfare
3 Microwave Photonics
4 Phase Sensitive Amplifiers

18. Meaning of Electronic Warfare
The use of electromagnetic spectrum to :
Detect Interception of enemy communication.
Exploit Use of acquired information to inflict damage on
enemy.
Inhibit Prevent the enemy to execute its offensives.

19. Russo-Japanese War
Figure: British cruiser HMS Diana
1904 HMS Diana at Suez canal intercepted Russian
wireless signals of mobilization of Russian fleet in
the eastern front. This message was passed to the
Japanese who were British allies. This helped the
Japanese win the Russo-Japanse war of 1904.

20. Battle of Beams in WWII
Figure: Reginald V. Jones (1911-1997)
1939 German aircrafts were bombing England at night
and bad weather. Jones, a young physicist
suspected the Germans were using radio waves for
communication. He looked for such signals near
bombing sights, but did not find them.

21. Battle of Beams in WWII
Figure: Transmitter beam shadow due to curvature of earth.
1939 Jones was not able to get the signals as he was
looking for it in the shadow region. Once he tried
it from an aircraft, he picked the signal.

22. Battle of Beams in WWII
Figure: Germans used the Knickbein system for aerial navigation.
1930 The Germans developed the Knickbein system for
aerial navigation. It worked in 30 MHz and used a
dot beam and a dash beam at an angle. The pilot
navigated in the constant tone region.

23. Battle of Beams in WWII
Figure: Knickbein system with an extra beam for bombing.
1939 An extra beam was used for bomb dropping.
When the pilot intersected, the extra tone he
dropped the bomb.

24. Battle of Beams in WWII

25. Battle of Beams in WWII
Figure: The British used a third beam of dots to confuse the pilot.
1939 As a counter measure, the British used a third
beam of dots to deceive the bombers. Thus most
of the dropped bombs fell short of target.

26. Battle of Beams in WWII

27. Beginning of Stealth Technology
Figure: Petr Ufimtsev (1931-present).
1964 Published a paper ”Method of edge waves in the
physical theory of diffraction”, describing
scattering of electromagnetic waves off different
surfaces. American company Lockheed developed
a software called Echo based on his theory.

28. Example of Stealth Technology
Figure: Lockheed F-117 Nighthawk.
1981 F-117 Nighthawk became the first stealth design
aircraft to be inducted in military. This design
reduced radar cross section by deflecting the
incoming waves. However it had low
maneuverability.
1991 Deployed successfully in the Gulf War.
1999 One aircraft downed in Yugoslavia by an
anti-aircraft missile in the Kosovo War.
2007 Retired from US Airforce.

29. Failure of Stealth Technology
Figure: Bomb door of a F-117 Nighthawk.
1 In spite of stealth design, the bomb-bay doors
when opened increased the radar cross section of
the aircraft.
2 It was designed for higher wavelength radars than
the radars were using. Bandwidth is important in
electronic warfare.

30. Modern Stealth Technology
Figure: Northrop Grumman B-2 Spirit Stealth Bomber.
1997 B-2 Spirit or Stealth Bomber was first inducted as
a nuclear weapon delivery platform. It has a
laminar shape devoid of sharp edges. It is coated
with radar absorbent material (probably tiny
spheres coated with ferrite). All these make it
almost radar invisible. (Details classified)
1999 First deployed successfully in the Kosovo War in
Serbia.

31. Phased Array Radar
Figure: Solid angle of scan of a directional radar antenna.
Problem To have a strong beam, the radar can only point
to one direction at a time. Thus to scan the sky
the antenna is mechanically rotated. This poses a
limitation on fast communication.
Solution Using a phased array antenna.

32. Phased Array Radar
Put phase difference φ between each adjacent antenna. The
resulting wavefront will propagate at an angle θ.

33. Phased Array Radar
Controlling φ we can change the beam direction.

34. Example of Phased Array Radar
Figure: Swathi weapon locating radar developed by DRDO.
1998 India wanted to buy high precision phased array
radars like AN/TPQ-37 Firefinder from USA and
France, but was turned down due to India’s
nuclear test at Pokhran the same year.
1999 Kargil war. India suffered high casualties due to
absence of a good radar.
2004 DRDO completed the first indigenous phased
array radar, Swathi. India is making it for 8.5
million USD each whereas the price of US made
AN/TPQ-37 was 17 million USD each.

35. Quantum Radar
Figure: Scheme of a quantum radar (Barjanjeh et al, 2020).
2015 Barjanjeh et al entangled microwave photons.
China claims to have this technology with a range
of 60 miles, while experts doubt it.
2020 Proof of concept of quantum radars at short length
scales. Field of ongoing research.

36. Quantum Radar

37. Contents
1 Electromagnetic Waves
2 Electronic Warfare
3 Microwave Photonics
4 Phase Sensitive Amplifiers

38. Meaning of Microwave Photonics
The optimized use of two different waves :
Microwaves 300 MHz(1 m) - 300 GHz(1 mm).
Photonics 30 THz(100 µm) - 300 THz(1µm).

39. Comparison of Microwaves and Photonics
Table
Attribute Microwaves Photonics
Wavelength High Low
Sensing resolution Low High
Atmospheric transparency High Low
Frequency Low High
Available bandwidth Low High
Transmission loss High Low
Conclusion
Microwaves are better for long range wireless sensing while
photonics is better for efficient data transmission link.

40. Transmission Loss Comparison of Coaxial Cables and
Optical Fibers

41. Microwave Photonic Link

42. E/O Conversion : Amplitude Modulation

43. Mach-Zehnder Modulator
Pockel’s effect is used to change the refractive index of a
medium on applying voltage.

44. Mach-Zehnder Modulator
Push-pull configuration leads to amplitude modulation.
Ein(t) = ξ0e−iωst + c.c.
Eout(t)
branch 2branch 1
Φ2(t) = −Φ1(t)Φ1(t)
MZM
(push-pull)

45. Mach-Zehnder Modulator
One Modulation Frequency : Ω
Modulation voltage Φ(t) :
Φ(t) = φ + A cos(Ωt). (1)
Output electric field Eout(t) :
Eout(t) =
ξ0
2
e−iωst
eiφ
eiA cos(Ωt)
+ e−iφ
e−iA cos(Ωt)
+ c.c. . (2)

46. Mach-Zehnder Modulator
Jacobi-Anger Identity
eiA cos(Ωt)
=
∞
n=−∞
in
Jn(A)einΩt
. (3)
where Jn is the Bessel function of first kind of order n.

47. Mach-Zehnder Modulator
One Modulation Frequency : Ω
Using Jacobi-Anger identity we get, Eout(t) :
Eout(t) =
ξ0
2
e−iωst
eiφ
∞
m=−∞
im
Jm(A)eimΩt
+ e−iφ
∞
p=−∞
ip
Jp(−A)eipΩt
+ c.c.
(4)

48. Mach-Zehnder Modulator
ω
Signal
ωs
ωs + Ω
ωs + 2Ω
ωs + 3Ω
ωs + 4Ω
Figure: Output spectrum of a Mach-Zehnder modulator with single
modulating frequency Ω. (Not to scale)

49. Mach-Zehnder Modulator
Two Modulation Frequency : Ω1, Ω2
Modulation voltage Φ(t) :
Φ(t) = φ + A (cos(Ω1t) + cos(Ω2t)). (5)
Output electric field Eout(t) :
Eout(t) =
ξ0
2
e−iωst
eiφ
∞
m=−∞
im
Jm(A)eimΩ1t
∞
n=−∞
in
Jn(A)einΩ2t
+ e−iφ
∞
p=−∞
ip
Jp(−A)eipΩ1t
∞
q=−∞
iq
Jq(−A)eiqΩ2t
+ c.c.
(6)

50. Mach-Zehnder Modulator
Large number of unwanted frequencies are generated.
ω
Signal
ω1,0ω0,1
ω2,1ω1,2
ω2,2
ω2,0
ω−2,2
ω1,−1
ωs = ω0,0
ω2,−2
ω−1,1
ω−1,2 ω2,−1
ω1,1
ω0,2
Ω1
Ω2
2Ω1 − Ω2
Figure: Output spectrum of a Mach-Zehnder modulator with two
modulating frequency Ω1 and Ω2. The frequencies are labelled as :
ωi,j = ωs + iΩ1 + jΩ2. (Not to scale)

51. Distortion in a Link
Two tone test
A modulator is modulated with two closely space
microwave frequencies.
Inter-modulation products are generated.
We look at the third order products (IMD3) and observe
its power as a function of the modulation power.
This helps us determine the operational range of the link.

52. Distortion in a Link
Figure: Spurious free dynamic range (SFDR) determines how
resistant the link is to distortion.

53. Distortion in a Link
Effect of amplification
What about optical amplification? Do we increase distortion
when we add an optical amplifier?

54. Contents
1 Electromagnetic Waves
2 Electronic Warfare
3 Microwave Photonics
4 Phase Sensitive Amplifiers

55. Linear Optics
Polarization
When an external electric field is applied to a material, it
creates dipoles. The dipole moment per unit volume is the
polarization P(t).
P(t) = 0χ(1)
E(t). (7)
where 0 is the electric permittivity of vacuum. χ(1) is the linear
susceptibility.

56. Nonlinear Optics
Nonlinear Polarization
In nonlinear optics, the optical response can be described by
expressing the polarization P(t) as a power series in the field
E(t) as :
P(t) = 0 χ(1)
E(t) + χ(2)
E(t)2
+ χ(3)
E(t)3
+ ... . (8)

57. Second Harmonic Generation
Frequency doubling
Electric field E(t) (scalar) is given by :
E(t) = E0e−iωt
+ c.c. . (9)
E(t)2
= 2E0E∗
0 + (E2
0e−i2ωt
+ c.c.) . (10)

58. Parametric Amplification
Nonlinear fiber : χ(2) = 0, χ(3) = 0
No frequency doubling as χ(2) = 0. But more complicated
four wave mixing processes due to χ(3) = 0.
Two pump photons can annihilate to create a signal and
idler photon.
ω
ωs ωP ωi
Signal
Pump
Idler

59. Parametric Gain
PIA vs PSA
PIA Only signal and pump is launched at input. Gain
of signal does not depend on relative phase of
waves.
PSA Signal, pump and idler is launched at input. Gain
of signal depends on relative phase between pump
signal and idler.

60. Parametric Gain
Relative phase Θ = 2θpump − θsignal − θidler.

61. Squeezed States of Light
Caves et al, 1982.

62. Microwave Photonic Link with PSA : Setup

63. Results
Thesis of Tarek Labidi 2017.
Conclusion
PSA does not degrade the SFDR of the microwave photonic
link.

64. Summary
Few basic concepts of electromagnetism.
History and overview of electronic warfare.
Role of microwave photonic links in radar systems.
What kind of amplifiers can be used for microwave
photonic links.
Does a phase sensitive amplifier add distortions to the link?
No!