le 428 antenna engineering - t u
TRANSCRIPT
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LE 428
Antenna Engineering
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Chapter 1 : Antennas
• Introduction
• Types of antennas
• Radiation mechanism
• Historical development
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Definition
• Definition of Antennas
– Webster’s : A usually metallic device (as a
rod or a wire) for radiating and receiving
radio waves
– IEEE’s : A means for radiating or receiving
radio waves
• In short, the transitional device (i.e., a
transducer) between free-space and a guiding device
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Antenna as a transition device
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Types of Antennas
• Wire Antennas
• Aperture Antennas
Dipole Circular (square) loop Helix
Pyramidal horn Conical horn Rectangular waveguide
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Types of Antennas (cont’d)• Microstrip Antennas
• Array Antennas
Rectangular Circular
Yagi-UdaAperture array
Microstrip patch array Waveguide slot antenna array
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Types of Antennas (cont’d)
• Reflector Antennas
• Lens Antennas
Convex-
plane
Convex-
convex
Concave-
planeConcave-
concave
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Radiation MechanismCurrent density Jz [A/m2]: , qv [C/m3]
Js [A/m]: , qs [C/m2]
Iz [A]: , ql [C/m]
Time-varying current:
zvz vqJ
zss vqJ
zlz vqI
zlz
lz aq
dt
dvq
dt
dI
zlz
lz alq
dt
dvlq
dt
dIl E
Jc
+vz
lx
V
z
z
y
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Radiation Mechanism (cont’d)
• To create radiation, needs a time-varying
current or an acceleration (or deceleration) of
charge, thus
– No moving charge, no current, no radiation
– Charge moving with uniform velocity:
• No radiation if the wire is straight and of infinite length
• Radiation if there is a discontinuity
– Radiation if charge oscillating in a time-motion
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Radiation Mechanism (cont’d)
• Single wire examples
curved bent
discontinuousterminated
truncated
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Radiation Mechanism (cont’d)
• Two-wire examples
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Current Distribution on two-wire
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Linear Dipole
2-wire transmission line
flared transmission line
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Intuitive
Picture of
Radiation
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Intuitive Picture of Radiation
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Historical Development
1873 Maxwell’s equations predict
electromagnetic radiation
1886 First wireless electromagnetic
system (Hertz)
1896 Wireless telegraph (Marconi)
1901 First transatlantic transmission
(Marconi)
1904 Radio broadcasting development;
First radio receiver; First
commercial broadcasting station
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Historical Development (cont’d)
1923 Television broadcasting
development; Yagi-Uda antenna
1938 Radar system development
1962 Satellite communication begins (1st
commercial satellite launched)
1978 First GPS satellite was launched
1979 First cellular phone network (1G)
1983 First cellular phone service in U.S.
1990s Digital cellular phone development
(2G)
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Historical Development (cont’d)
1998 The start of Bluetooth
1999 WiFi standard released (802.11)
1999 First wireless LAN in Apple iBook
was announced
2000 Camera phone introduced
2001 WiMAX standard released (802.16)
2004 WiFi devices (PDA, cell-phone, etc.)
introduced
2007 Smart phone introduced (iphone)