An Introduction to Antennas

for Space Applications Lesson 2

Dr. ing. Marco Lisi (marco.lisi@ieee.org)

Space Challenges, Sofia, 2015

Outline

LESSON 2

• Satellite antenna footprints • Satellite orbits • The geostationary (Clarke’s) constellation • Global coverage antennas • Elliptic coverage antennas • Spot coverage (multi-beam) antennas • Contoured coverage (shaped-beam) antennas • Beam-forming networks (BFN’s) • Parabolic reflector antennas • Phased-array antennas • Active array antennas

2

Satellite Antenna Footprint

3

The antenna footprint is the area on the Earth illuminated by the antenna with a specified minimum gain.

Iso-gain or Iso-EIRP Contours

4

On the antenna footprint it is possible to trace the iso-gain contours. In case of satellites for TV broadcasting, it is usually reported the EIRP (“Effective Isotropic Radiated Power”), in dBW, or the corresponding needed diameter of the ground antenna.

Satellite Orbits

Geostationary Orbit

6

The Clarke’s Constellation

7

Global Coverage from GEO Orbit

8

Global Coverage Antenna

9

d θ3dB = 17.5º

d = circular aperture diameter

𝜃𝜃3𝑑𝑑𝑑𝑑 = 70 λ𝑑𝑑 𝐺𝐺𝑚𝑚𝑚𝑚𝑚𝑚 = η (𝜋𝜋𝑑𝑑

λ)2 η= 0.55

𝐺𝐺𝑚𝑚𝑚𝑚𝑚𝑚 = 20 dB @ 4 GHz, d ≅ 0.3 m (horn antenna)

Global Coverage from GEO Constellation

10

Evolution of Satellite Antennas

11

Elliptic Coverage (Europe)

12

Satellite Elliptic Coverage (North America)

13

Spot beam Antenna

Multi-beam Coverage (Eutelsat W2A)

Shaped Beam Antenna The coverage area is shaped to fit at best the service area: • By shaping the antenna reflector (e.g. elliptical reflector); • By using multiple feed antennas

16

Shaped Beam Antenna (multi-feed)

17

Feed Array

Reflector

A B

C D

D

C

B

A

Feed Array

Reflector

Contoured Coverage

18

Beam-Forming Networks

19

The Parabolic Reflector

20

Parabolic Reflector Antennas

A paraboloid is the surface generated by a parabola revolving around its axis. The parabolic reflector functions due to the geometric properties of the paraboloidal shape: any incoming ray that is parallel to the axis of the dish will be reflected to a central point, or "focus".

21

Parabolic Antenna Configurations

22

Front-fed Reflector Antenna

23

Off-set Fed Reflector Antenna

24

On-set and Off-set Cassegrain

Real Focus

Virtual Focus

Hyperbolic Subreflector

Virtual Equivalent Reflector

D

25

On-set and Off-set Gregorian

1st Ellipse Focus

2nd Ellipse Focus

Elliptic Subreflector

Virtual Equivalent Reflector

D

26

Phased-Array Antennas

GPhased-Array (dBi) = G Single Element (dBi) + 10 x log10 N

27

Phased-Array Antennas: Globalstar

28

Phased-Array Antennas: Galileo

29

Active Array Antennas: Cosmo-Skymed

30

Korean

Thank You English

Russian

Danke German

Grazie Italian

Gracias Spanish

Obrigado Brazilian

Portuguese Arabic

Traditional Chinese

Thai

Merci French

Japanese

Благодаря Bulgarian

תודהJewish