EEE381B Aerospace Systems

1
EEE381BAerospace Systems Avionics

• Foundation
• Waves Propagation
• Plus a dB tutorial

2
Outline

• Electromagnetic spectrum
• Wave propagation
• Basic wave characteristics
• Aside dB in review
• Propagation losses
• The link equation
• In-class exercises

3
1. The EM spectrum
4
1.1.1 EM spectrum components

• DC to light, and beyond
• Radio
• Infrared
• Visible (optical)
• Ultraviolet
• X-Rays
• Gamma Rays

Increasing Frequency
Increasing Energy
Decreasing Wavelength
5
1.2.1 The radio spectrum

• DC to 300 GHz
• 30-300 Hz Extremely Low Frequency ELF
• 300-3000 Hz Ultra Low Frequency (Voice
  Frequency) ULF (VF)
• 3-30 KHz Very Low Frequency VLF
• 30-300 KHz Low Frequency LF
• 300 KHz-3 MHz Medium Frequency MF
• 3-30 MHz High Frequency HF
• 30-300 MHz Very High Frequency VHF
• 300 MHz-3 GHz Ultra High Frequency UHF
• 3-30 GHz Super High Frequency SHF
• 30-300 GHz Extra High Frequency EHF

6
1.3.1 Military Avionics spectrum
7
1.3.2 Military Avionics spectrum
Infrared
Visible
Radio Frequency
Ultraviolet
Millimeterwave
Microwave
LF / MF / HF / VHF / UHF
Near
Mid
Long
Laser
Synthetic Aperture Radar
Night Imaging
Fire Control Combat ID
Ground Penetrating Radar
UV Threat Warning
8
1.4.1 DND Spectrum Use
Largest user in Canada
9
1.4.2 DND Spectrum Use
10
2. Wave propagation

• The energy in an electromagnetic (radio) wave
  exists partly in the form of its electric field
  and partly in the form of its magnetic field.

This is an MIT OpenCourseWare movie4 that
demonstrates the propagation of a wave in free
space.
11
2.1 Electric fields

• An electric field exists in the presence of a
  charged particle.
• Whenever an electric field flows, a magnetic
  field is produced.
• If the electric field varies sinusoidally so too
  will the magnetic field.

12
2.2 Magnetic fields

• A magnetic field exists around electric currents,
  magnetic dipoles, and changing electric fields.
• Whenever a magnetic field flows, an electric
  field is produced.
• Moving a magnet back and forth within a coil
  induces an alternating current.

13
3. Basic wave characteristics

• Speed
• Direction
• Polarization
• Intensity
• Wavelength
• Frequency
• Period
• Phase

14
3.1 Speed of radio waves (c)

• In a vacuum, radio waves travel at the speed of
  light.
• c 299.7925 x 106 meters / second
• In the atmosphere, depending upon pressure and
  temperature, radio waves travel slightly slower.
• 299.7122 x 106 meters / second

We will mostly use c 300 x 106 m/s
15
3.2 Direction of propagation
E

• In free space, a waves magnetic field (H) is
  always orthogonal to the electric field (E).
• The direction of wave travel is always orthogonal
  to both.

H
16
3.3 Polarization
E

• The polarization of a wave refers to the
  orientation of the E and H fields.
• By convention polarization is stated in terms of
  the E field.
• Examples include vertical, horizontal,

H
17
3.4 Intensity

• The intensity of a wave is the rate at which it
  carries energy through space, and is the product
  of the two field strengths.
• Power density is a measure of the waves average
  intensity over time.
• The power of a received signal is then the power
  density times the area of the receiving device
  (antenna).

18
3.5 Wavelength (?)

• The physical distance between two successive
  crests of the waves undulating intensity defines
  its wavelength.
• Wavelength is usually given in meters.

Wavelength, ?
19
3.7 Frequency (f)

• The number of cycles per second defines the
  waves frequency.
• f c/? (in Hertz, Hz)

f1 3 f2
20
3.7 Periodicity (T)

• The period of a wave is another measure of its
  frequency. It is the length of time it takes to
  complete one cycle.
• T 1/f

Period, T
21
3.8 Phase (F)

• The phase difference between two waves is the
  degree to which one signal differs in time from
  another wave of the same frequency.
• Usually measured in angles (radians).

Phase, F
22
4. Aside dB in review

• Logarithms
• dB as a ratio
• dB as an absolute

23
4.1 Logarithms

• Unless stated otherwise logarithms are to the
  base 10 ie, log10(x)is simply log(x)
• log(ab) log(a) log (b)
• example
• log(200) log(2x 102)
• log 2 log 102
• 0.3 2

10n
N
N 10n Log10 N n
10
Only need to know logarithms for numbers between
1 and 10.
24
4.2 The decibel (dB) as a ratio

• The decibel is a logarithmic unit devised to
  express (power) ratios.
• Power ratio in dB 10 log10 (P2 / P1)

Decibels
Power Ratios
25
4.3 The decibel (dB) as an absolute

• Decibels can also be used to express absolute
  values in relation to some reference
• For example, by convention
• dBW dB value of power / 1 watt
• dBm dB value of power / 1 milliwatt
• Therefore
• 1.6 kilowatts 32 dBW or 62 dBm

26
4.4 The advantage of the decibel (dB)
The large, short range target may reflect more
than 10,000,000,000,000 times power than the
distant smaller target.
10-13 milliwatt -130 dBm
1 milliwatt 0 dBm
27
5. Propagation losses

• Spreading losses
• The spreading loss, or space loss, is the
  free-space propagation loss which accrues with
  distance travelled.
• Atmospheric losses
• The atmospheric loss is an additional propagation
  loss that accounts for the fact that energy is
  absorbed by the atmosphere.

28
5.1.1 Spreading loss equation, LS

• For line of sight propagation in good weather,
  spreading loss can be estimated as follows
• LS 20 log(4pr/?) , units dB
• where r is the distance in same units as ?,
• or as
• LS (dB) 32.4 20 log (dkm) 20 log (fMHz)

This last equation is only valid for the units
specified!
29
5.1.2 Spreading loss nomograph2
30
5.2.1 Atmospheric losses, LA

• Atmospheric attenuation is a nonlinear function
  of the signal frequency, and instead of an
  equation, a graph is typically used.
• Note from the next slide that the atmospheric
  loss is quite low for many RF applications.

31
5.2.2 Atmospheric loss monograph2
32
6. The link equation 2
33
6.1 Link equation example

• Transmitter power 1W 30 dBm
• Transmitter antenna gain 10 dB
• Spreading loss 100 dB
• Atmospheric loss 2 dB
• Receiving antenna gain 3 dB
• Receiver Power -59 dBm

34
7. In-class exercises
35
7.1 Quick response exercise 1

• What is the wavelength of
• an HF signal that operates at 3.5 MHz?
• the signal of AM radio station Fan590?
• a SATCOM operating at 1.6265 GHz?
• What is the period of
• the SATCOM signal above?

36
7.2 Quick response exercise 2

• From the example in section 6, what is the power
  of the signal at the receiver in Watts?

37
7.3 Link equation calculations

• Given a 20 GHz 5kW transmitter equipped with an
  antenna that yields a fourfold power gain, what
  is the received power in milliwatts at a matched
  zero gain receive antenna 400 km away?

38
References

• Moir Seabridge, Military Avionics Systems,
  American Institute of Aeronautics Astronautics,
  2006. Sections 2.6 2.7
• David Adamy, EW101 - A First Course in
  Electronic Warfare, Artech House, 2000.
  Chapters 2 3
• Antenna Fundamentals, laboratory manual, Lab-Volt
  (Quebec) Ltd, 1996. Unit 1
• Electromagnetics and Applications, 6.013, Fall
  2002, MIT OpenCourseWare, http//ocw.mit.edu/OcwWe
  b/Electrical-Engineering-and-Computer-Science/6-01
  3Electromagnetics-and-ApplicationsFall2002/CourseH
  ome/index.htm
• George W. Stimson, Introduction to Airborne
  Radar, SciTech Publishing Inc., 1998.
• Mark A. Hicks, "Clip art licensed from the Clip
  Art Gallery on DiscoverySchool.com"