Part 1 of my short introduction to antennas for space applications. Space Challenges, Sofia, September 2015

1. An Introduction to
Antennas
for Space Applications
Dr. ing. Marco Lisi
(marco.lisi@ieee.org)
Space Challenges, Sofia, 2015

2. “(…) et homines dum docent discunt”
Lucius Annaeus Seneca (c. 4 BC – A.D. 65)
Epistulae Morales ad Lucilium, Liber I, 7-8
2

3. Course Objectives
• To explain what antennas are, why they are important
in our every day life and why they are so especially key
in space applications;
• To explain some fundamental concepts and definitions
about antennas;
• To suggest some quick and dirty methods to evaluate
the performance of an antenna, with almost no
mathematics and just a few formulas involved;
• To offer a synthetic overview of antenna technologies
and configurations for on-board satellite applications.
3

4. Outline
LESSON 1
• Etymology of the word “antenna”
• Electromagnetic waves and electromagnetic spectrum
• Wavelength and period
• The antenna as a transducer
• Reciprocity principle
• Antenna directivity and beam patterns
• Antenna polarization
• How to calculate directivity and gain
• Antenna beam-width and gain-area product
• Antenna temperature
4

5. Antennas are everywhere…
5

6. …and very important in space applications
6

7. Antenna Etymology
• From Latin antenna, nautical term for yard and common
term for pole, of uncertain origin, but possibly from Proto-
Indo-European *temp- (“to stretch, extend”).
7

8. Antenna Etymology
The origin of the word antenna relative
to wireless apparatus is attributed to
Italian radio pioneer Guglielmo
Marconi.
In the summer of 1895, Marconi
began testing his wireless system
outdoors on his father's estate near
Bologna and soon began to
experiment with long wire "aerials".
Marconi discovered that by raising the
"aerial" wire above the ground and
connecting the other side of his
transmitter to ground, the transmission
range was increased.
Soon he was able to transmit signals
over a hill, a distance of approximately
2.4 kilometres (1.5 mi).
In Italian a tent pole is known as
“l'antenna centrale”, and the pole with
the wire was simply called “l'antenna”.
8

9. Antennas “radiate” EM Waves
9

10. The Electromagnetic Spectrum
10

11. Electromagnetic Wave E and H fields
11

12. EM Waves Wavelength and Period
12
λ = c T =
𝒄𝒄
𝑭𝑭
c = speed of light = 3 𝟏𝟏𝟏𝟏𝟖𝟖 m/s
λ (m) =
𝟎𝟎.𝟑𝟑
𝑭𝑭 (𝑮𝑮𝑮𝑮𝑮𝑮)

13. The Antenna as a Transducer
13

14. From guided wave to free space wave
14

15. The Principle of Reciprocity
15
Reciprocity is one of the most useful (and fortunate)
property of antennas.
Reciprocity states that the receive and transmit
properties of an antenna are identical. Hence, antennas
do not have distinct transmit and receive radiation
patterns - if you know the radiation pattern in the
transmit mode then you also know the pattern in the
receive mode.
NOTA BENE: the reciprocity does not apply to active
antennas, i.e. antennas that include active components,
such as low-noise amplifiers (receive antennas) and
power amplifiers (transmit antennas)

16. Antenna Directivity (1/2)
16

17. Antenna Directivity (2/2)
17

18. Definition of Directivity
• The directive gain of an antenna measures the power
density the antenna radiates in one direction, versus the
power density radiated by an ideal isotropic radiator (which
emits uniformly in all directions) radiating the same total
power;
• The directive gain, D(θ, φ), depends on the direction;
• The directivity D of an antenna is the maximum value of its
directive gain;
• The directivity is usually expressed in dBi, which is ten time
the logarithm (base 10) of the ratio defined before:
D (dBi) = 10𝑙𝑙𝑙𝑙 𝑙𝑙10 (
𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 𝑑𝑑 𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 𝑖𝑖𝑖𝑖 𝑜𝑜𝑜𝑜𝑜𝑜 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 𝑑𝑑
𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 𝑑𝑑 𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖 𝑖𝑖
)
18

19. Azimuth and Elevation
19

20. Antenna Patterns in 3D and 2D
20
3D
2D Polar Cuts 2D Rectangular Cuts

21. Antenna Radiation Pattern (1/2)
21

22. Antenna Radiation Pattern (2/2)
22

23. Which of the two is more directive?
23

24. Antenna Polarization (1/3)
24
Linear Polarization: Vertical (“V”) or Horizontal (“H”)
Circular Polarization: Right Hand Circular Polarization (“RHCP”) or
Left Hand Circular Polarization (“LHCP”)

25. Antenna Polarization (2/3)
25
• Polarization is defined as the orientation of the electric field
of an electromagnetic wave. Polarization is in general
described by an ellipse. Two special cases of elliptical
polarization are linear polarization and circular polarization.
• When the electric field always lays in the same plane, we
speak of linear polarization (either vertical or
horizontal).Two orthogonal linearly polarized EM waves
can propagate without interfering to each other.
• If the electric field rotates while propagating (either
clockwise or counter-clockwise) we speak of circular
polarization. Two circularly polarized EM waves with
opposite rotations are also orthogonal.

26. Antenna Polarization (3/3)
26
• A linearly polarized EM wave and a circularly polarized one
are not orthogonal.
• An antenna designed to receive (or transmit) in linear
polarization would experience up to a 3dB loss in receiving
a circularly polarized EM wave.
• Orthogonal polarizations are often used in satellite
communications systems to effectively double the available
frequency bandwidth.

27. Antenna Cross-Polarization
27
• An antenna is never 100% polarized in a single mode
(linear, circular, etc);
• Cross polarization (X-pol) is the polarization orthogonal to
the polarization being discussed. For instance, if the fields
from an antenna are meant to be horizontally polarized, the
cross-polarization in this case is vertical polarization. If the
polarization is Right Hand Circularly Polarized (RHCP), the
cross-polarization is Left Hand Circularly Polarized (LHCP);
• The cross polarization is specified for an antenna as a
power level in negative dB, indicating how many decibels
below the desired polarization's power level the x-pol power
level is.

28. Directivity Formula
D = ηrad
𝟒𝟒𝝅𝝅 𝑨𝑨𝒆𝒆𝒆𝒆𝒆𝒆
𝝀𝝀𝟐𝟐
where:
Aequ = is the equivalent area of the antenna (in case of an
aperture antenna like a reflector or a patch is the
physical area of the antenna);
λ = the electromagnetic wave wavelength;
ηrad = the radiation efficiency (including several non-ohmic,
i.e. non-dissipative, losses)
28

29. Antenna Directivity Nomogram
29

30. Directivity ≠ Gain
30
G = ηohmic D
in dB: G (dB) = D (dBi) - Lohmic (dB)

31. Beamwidth Formula
The Half Power Beamwidth (HPBW) is the angular separation
in which the magnitude of the radiation pattern decrease by
50% (or -3 dB) from the peak of the main beam.
HPBW (degrees) = k
λ
𝒅𝒅
where:
k = factor (in degrees) that depends from the type of aperture
(70 in case of circular aperture, such as reflectors);
d = physical dimension of the aperture (diameter in case of
circular aperture).
31

32. Gain Area Product (1/2)
Approximating the antenna pattern as a rectangular area:
D =
𝑨𝑨𝑨𝑨𝑨𝑨𝑨𝑨 𝒐𝒐𝒐𝒐 𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔
𝑨𝑨𝑨𝑨𝑨𝑨𝑨𝑨 𝒐𝒐𝒐𝒐 𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂𝒂 𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑
=
𝟒𝟒𝝅𝝅𝒓𝒓𝟐𝟐
𝒓𝒓𝟐𝟐 𝒔𝒔𝒔𝒔 𝒔𝒔 𝜽𝜽𝟑𝟑𝟑𝟑𝟑𝟑 𝒔𝒔𝒔𝒔 𝒔𝒔(∅𝟑𝟑𝟑𝟑𝟑𝟑)
≅
𝟒𝟒𝟒𝟒
𝜽𝜽𝟑𝟑𝟑𝟑𝟑𝟑∅𝟑𝟑𝟑𝟑𝟑𝟑
In degrees:
D =
𝟒𝟒𝟒𝟒𝟒𝟒𝟒𝟒𝟒𝟒
𝜽𝜽𝟑𝟑𝟑𝟑𝟑𝟑∅𝟑𝟑𝟑𝟑𝟑𝟑
32

33. Gain Area Product (2/2)
33

34. Antenna Noise Temperature, Ta
The temperature of a hypothetical resistor that would generate the same output
noise power per unit bandwidth as that at the antenna output at a specified
frequency.
The antenna noise temperature depends on antenna coupling to all noise sources
in its environment as well as on noise generated within the antenna.
34

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