Paper Title - KEMT FEI TUKE
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-1-
Introduction to
Antennas & Propagation
Antennas
&
Propagation
Wu Qun
- Review of Lecture VI
-2-
Introduction to
Antennas & Propagation
Overview of Lecture VII
-
Frequency Independent Antennas
-
Basics of Aperture Antennas
-
Horn Antenna
-
Slot Antenna
-
Microstrip (Patch) Antenna
-
Parabolic Antenna
- Antennas:
Practical Considerations
-3-
Introduction to
Antennas & Propagation
Review
-4-
Introduction to
Antennas & Propagation
Wire Antennas
1.
Hertzian Dipole
2.
Finite Length Dipole
3.
Antenna Array
4.
Uda-Yagi
5.
Turnstile
6.
Loop
7.
Helix
8.
Quadrifilar Helix
Uda-Yagi Antenna
-5-
Introduction to
Antennas & Propagation
VHF TV Receive Antenna
Sheet Reflector
Folded Dipole
Driver
Feeding Mast
5-6 Directors
Helical Antenna
3/4 < C/ < 4/3
-6-
Introduction to
Antennas & Propagation
Axial Mode Radiation (endfire) appears if:
1.
sidelobes
z
2.
HPBW 1/(Number of turns)
3.
Circular Polarisation
(orientation helix orientation)
y
x
Narrow Mainbeam with minor
4.
Wide Bandwidth
5.
No coupling between elements
6.
Supergain Endfire Array
Circumference C
-7-
Introduction to
Antennas & Propagation
Frequency Independent
Antennas
All antenna characteristics so far were always scaled with respect
to . Thus, changing changes the characteristic.
-8-
Introduction to
Antennas & Propagation
Rumsey’s Principle
The impedance and pattern properties
of an antenna will be frequency
independent if the antenna shape is
specified only in terms of angles and
the antenna itself is infinite.
Scaling through angles
Infinite size
self-scaling
problem of realisation
-9-
Introduction to
Antennas & Propagation
Rumsey’s Principle
Finite Bowtie Antenna
Effectively infinite
current decays fast
Current decays fast
introduce discontinuities
Discontinuities
destroy self-scaling nature
Self-scaling nature
log-periodic toothed antenna
-10-
Introduction to
Antennas & Propagation
Log-periodic toothed Antenna
Log-periodic sheet
Log-periodic wire
Characteristic will be repeated at (discrete) nf1.
-11-
Introduction to
Antennas & Propagation
Log-periodic Dipole Array
-12-
Introduction to
Antennas & Propagation
Spiral Antenna
-13-
Introduction to
Antennas & Propagation
Fractal Antenna
-14-
Introduction to
Antennas & Propagation
Aperture Antennas
Any wavefront can be considered to be the
source of secondary waves that add to produce
distant wavefronts.
z
-15-
Introduction to
Antennas & Propagation
Huygen’s Principle
en
r’
P
r
J,
x
k
E j
4
y
e jkr'
en Es er' en Hs er' er' d
r'
Surface
Aperture Plane
-16-
Introduction to
Antennas & Propagation
Aperture Plane
-
E-field vanishes on the
Hemisphere at infinity.
- Total
field is derived from
the knowledge of the field
Closing Hemisphere
on the aperture plane.
y
r’
x
b/2
r
P
E A E0 e y
H A E0 / e x
z
-17-
Introduction to
Antennas & Propagation
Rectangular Aperture
-a/2
a
Polarisation in the far field is the
same as in the aperture.
1
1
sin
ka
sin
cos
sin
kb
sin
sin
k e jkr
2
2
E j
E0 a b
1
1
4 r
ka sin cos
kb sin sin
2
2
sin 1 cos e θ cos 1 cos e φ
y-z plane:
-18-
Introduction to
Antennas & Propagation
Parameter Rectangular Aperture
1
sin
kb
sin
k e jkr
2
1 cos
E yz j
E0 a b
1
4 r
kb sin
2
HPBW yz 0.886
b
x-z plane:
1
sin
ka
sin
k e jkr
2
1 cos
E yz j
E0 a b
1
4 r
ka sin
2
HPBW xz 0.886
a
y
r’
x
r
-19-
Introduction to
Antennas & Propagation
Circular Aperture
P
E A E0 e y
H A E0 / e x
z
a
Polarisation in the far field is the
same as in the aperture.
k e jkr
J 1 ka sin
2
E j
E0 a
2 r
ka sin
sin 1 cos e θ cos 1 cos e φ
J1(x) is the first order Bessel Function of first kind.
y-z plane:
k e jkr
J ka sin
E yz j
E0 a 2 1
1 cos
2 r
ka sin
-20-
Introduction to
Antennas & Propagation
Parameter Circular Aperture
x-z plane:
k e jkr
J 1 ka sin
2
E xz j
E0 a
1 cos
2 r
ka sin
Large Apertures:
HPBW 58
2a
Directivity
Drec
4
2
a b
Dcirc
4
2
Definition
Real Physical Area
Circular Aperture:
-21-
Introduction to
Antennas & Propagation
Rectangular Aperture:
a
D
2
4
2
Ae
Thus, for the uniform rectangular and circular aperture the
physical area is equal to the effective area.
Non-uniform apertures or fields:
Ae ap Aph
ap
… Aperture Efficiency
Aperture Antennas: 30-90%
Horn Antennas:
50%
-22-
Introduction to
Antennas & Propagation
Horn Antennas
Horn Antennas
E-Plane
H-Plane
Pyramidal
sectoral horn
sectoral horn
horn
-23-
Introduction to
Antennas & Propagation
TE10
Excitation: TE10 mode
Impedance Matching
through flare
Gradual Transmission with
minimised reflection
-24-
Introduction to
Antennas & Propagation
Specifications
1.
Directive Radiator
2.
Primary feed for parabolic reflectors
3.
High gain, wide bandwidth and simple
4.
Particularly used in microwave region (>1GHz)
5.
Fan radiation patterns
-25-
Introduction to
Antennas & Propagation
Slot Antennas
Slot Antennas
-x
L
V
1
E A sin k L z e x
w 2
y
-26-
Introduction to
Antennas & Propagation
z
w
1
1
kL cos cos kL
jkr cos
V e
2
2 e
E( r ) j
φ
r
sin
Bookers Principle:
Z dipole 73 j 42.5
Z air Z metal
2
4
35476 2
Z slot ( / 2) 363 j 211
TE10 mode
-27-
Introduction to
Antennas & Propagation
Slot on Waveguide Walls
Radiation is maximum at maximal interrupted current
Radiation
No Radiation
-28-
Introduction to
Antennas & Propagation
Applications
1.
Slot Antennas are used in fast-moving vehicles.
2.
The slot-length is usually /2
3.
Particularly used in microwave region (>1GHz)
-29-
Introduction to
Antennas & Propagation
Microstrip (Patch)
Antennas
Patch
Feed
-30-
Introduction to
Antennas & Propagation
Patch Structure
Substrate
L
---++++
r
++++ t
----
d
Patch Shapes
-31-
Introduction to
Antennas & Propagation
Rectangular
Dipole
Circular Ring
Elliptical
Analysing Methods
Triangular
-Transmission
Line
-
Cavity
-
Maxwell Equations
1.
It is applied where small antennas are required:
aircrafts, mobiles, etc
2. Due to shape variations they are versatile in
-32-
Introduction to
Antennas & Propagation
Application & Performance
polarisation, pattern, impedance, etc.
3. They have a low efficiency, spurious feed
radiation and a narrow bandwidth
4. They usually operate in broadside regime
5. /3 < L < /2 and 2 < r < 12
-33-
Introduction to
Antennas & Propagation
Parabolic Reflector
Antennas
Large Gains
Uda-Yagi:
-34-
Introduction to
Antennas & Propagation
1.
15dB
Complicated Feeding
2.
Helical Antenna:
15dB
3.
Antenna Arrays
high gains many elements
4.
Horn:
high gains large size
Aperture increasing Reflector
Artificially increase size
-
(re-) transmitted waves are in phase
-
(re-) transmitted waves are as parallel as possible
Parallel and in-phase waves
Parabolic Dish
D
4
2
Ae
Feed
-35-
Introduction to
Antennas & Propagation
Parabolic Reflector
D
-
Dish has to be 100% parabolic
-
Feeder shouldn’t block too much
Non-uniform fields due to aperture blocking etc
Ae ap Aph
ap
… Aperture Efficiency = 80%
4
2
r 2
Applications
Used where high gains are required:
Cosmic Radiation, etc.
2.
Navigation
1.
Beam is slightly steerable
2.
Deviation from perfect surface can be made
-36-
Introduction to
Antennas & Propagation
1.
<1mm
3.
Diameters are usually 100m-300m
-37-
Introduction to
Antennas & Propagation
Practical Considerations
- The Quality Factor Q
- Electrically Small Antennas
-38-
Introduction to
Antennas & Propagation
Practical Considerations
- Physically Small Antennas
- Imperfect Ground
-39-
Introduction to
Antennas & Propagation
Feeding
- Fractal Antennas
- Light Antennas
-40-
Introduction to
Antennas & Propagation
‘Exotic’ Antennas
- Gravity Antennas
Everything what propagates can be transmitted.
Everything what can be transmitted can be received.
- EM waves, sound, smell, light, gravity and maybe 6th sense -