Antenna Design 2014
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Transcript of Antenna Design 2014
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Antenna Design
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Outline
Introduction
Fundamental Antenna Parameters
Design Methodology
Examples:
microstrip patch antennas
slot antennas
Yagi-Uda antennas
others antennas
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Introduction
The antenna (aerial, EM radiator) is a device, which radiates or
receives electromagnetic waves
The antenna is the transition between a guiding device (transmission
line, waveguide) and free space (or another usually unbounded medium)
Conductor or group of conductors used either for radiating
electromagnetic energy into space or for collecting it from space
The electromagnetic radiation from an antenna is made up of two
components, the E field and the H field
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Antennas are reciprocal devices: properties are similar both in
the transmitting mode and the receiving mode
(example: radiation pattern)
The electrical and electromagnetic characteristics of an antenna
apply equally, regardless of whether you use the antenna for
transmitting or receiving.
Microwave circuit
(electric power)
Free space
(electromagnetic
power)
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Matching device from a transmission line to the free
space and vice versa
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Types of antenna
Wire Antennas
Aperture Antennas
Microstrip & printed
Antennas
Reflector Antennas
Lens Antennas
Array Antennas
dipole monopole loop
pyramidal horn
slot
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Types of antenna
Wire Antennas
Aperture Antennas
Microstrip & printed
Antennas
Reflector Antennas
Lens Antennas
Array Antennas
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Types of antenna
Wire Antennas
Aperture Antennas
Microstrip & printed
Antennas
Reflector Antennas
Lens Antennas
Array Antennas
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The space surrounding the antenna is divided into three regions
according to the predominant field behavior (the boundaries
between the regions are not distinct)
Reactive near-field region
Radiating near-field region
Far-field (Fraunhofer) region
(transverse EM wave)
where:
D is the largest dimension of the antenna
λ is the wavelength
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Near field Far field
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Feeding transmission lines
rectangular metal waveguide microstrip line
coplanar waveguide coaxial line parallel-wire line
E
electric field
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Fundamental Antenna Parameters
Radiation pattern
Pattern beamwidth
Directivity
Input impedance
Antenna gain
Frequency bandwidth
Microwave circuit
(electric power)
Far field
(electromagnetic
power)
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Radiation pattern
The radiation pattern (RP)
(or antenna pattern) is the
representation of the radiation
properties of the antenna as a
function of space coordinates
The pattern can be a 3-D plot
(both θ and ϕ vary), or a 2-D plot
A 2-D plot is obtained as an
intersection of the 3-D one with a
given plane, usually a const θ=
plane or a . const ϕ= plane that
must contain the pattern’s maximum Spherical coordinate system
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Radiation pattern
An isotropic antenna that radiates
at an equal strength to all directions is a
good reference antenna but is not
realizable in practice.
Omnidirectional antenna is an
antenna, which has a non-directional
pattern in a given plane, and a
directional pattern in any orthogonal
plane.
Directional antenna is an antenna,
which radiates (receives) much more
efficiently in some directions than in
others.
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describe the antenna
resolution properties
Radiation pattern
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Radiation pattern:
polarization
E
electric field
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Directivity
Directivity of an antenna in a given direction is the ratio of the radiation
intensity in this direction and the radiation intensity averaged over all
directions.
The radiation intensity averaged over all directions is equal to the total power
radiated by the antenna divided by 4 π. It is a measure of the antenna’s ability
to focus the energy in one or more specific directions.
directivity of an isotropic source = 1 (0 dBi)
isotropic
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Input impedance (return losses)
ZA= RA+ j XA
RA is the antenna resistance
XA is the antenna reactance
RA= RL + Rrad
Rrad is the radiation resistance
RL is the loss resistance
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Input impedance (return losses)
The antenna input impedance is frequency dependent. Thus, it is
matched to its load in a certain frequency band. It can be influenced
by the proximity of objects, too.
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Input impedance (return losses)
Resonant antenna Wideband antenna
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Antenna gain
The gain G of an antenna is the ratio of the radiation intensity U in a
given direction and the radiation intensity that would be obtained, if the
power fed to the antenna Pin were radiated isotropically.
Antenna gain includes:
Mismatch losses
Losses in the transmission line
Losses in the antenna: dielectric losses, conduction losses,
polarization losses
Gain ≤ Directivity Gain = η Directivity
η – antenna efficiency [%]
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Frequency bandwidth (FBW)
This is the range of frequencies, within which the antenna characteristics
conform to a specified standard.
Antenna characteristics, which should conform to certain requirements,
might be: input impedance, radiation pattern, beamwidth, polarization,
side-lobe level, gain, beam direction and width, radiation efficiency. Often,
separate bandwidths are introduced: impedance bandwidth, pattern
bandwidth, etc.
broadband antennas narrowband antennas
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Design Methodology
1. Analytical estimation of the main layout dimensions at the
central operating frequency
2. Optimization of the antenna performances in terms of radiation
pattern, antenna gain and reflection losses using intensive
electromagnetic simulations
3. Manufacturing and testing of the antenna demonstrators
4. Design and optimization of the antenna structures for a given
application, integrated with other circuit element into a receiver
or transmitter front-end.
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Planar antennas
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End-fire radiation pattern
Broadside radiation pattern
Types of planar antennas
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Electromagnetic simulations
IE3D Zeland Software Inc., Freemont, CA, full wave,
Method-of-Moments (MoM) simulator
performs electromagnetic analysis for arbitrary 3-D
planar geometry maintaining full accuracy at all
frequencies.
the electromagnetic analysis includes dispersion,
discontinuities, surface waves, higher order modes,
metallization loss and dielectric loss
optimization engine that allows the using of multiple
objective function
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Electromagnetic simulations
MoM electromagnetic simulators are, according to
their solution domains, divided into two groups:
Open boundary Green’s function formulations;
Close boundary Green’s function formulations
(Sonnet, AWR Microwave Office, etc).
exact boundary conditions for most antennas and
many different RF and microwave circuits.
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Duality in Maxwell’s equations
The electromagnetic (EM) field is described by two sets of quantities,
which correspond to each other in such a manner that substituting the
quantities from one set with the respective quantities from the other set
in any given equation produces a valid equation (the dual of the given
one).
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Duality in Maxwell’s equations
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Slot antenna Dipole antenna
Similar radiation characteristics …
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Slot antenna Dipole antenna
… but different input impedances
≈ 73 Ω ≈ 495 Ω
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Duality in Maxwell’s equations
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Microstrip patch antennas
small, light, and suitable for integration and mass-production
typically rectangular, half-wave-long patch
easy to be integrated into antenna arrays
rectangular microstrip antenna fed by a microstrip line
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Analytical Design
Input: 2 < εr < 12; fo; h
1. For good radiation efficiency:
2. Effective dielectric constant:
3. Fringing effect:
4. Patch length:
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Input impedance
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Aperture Coupled Microstrip Antenna
Coaxial line feed antenna substrate dielectric constant: bandwidth and
radiation efficiency of the antenna
antenna substrate thickness: bandwidth and coupling level
microstrip patch length: resonant frequency of the antenna
microstrip patch width: resonant resistance of the antenna
feed substrate dielectric constant: good microstrip circuit
slot length: coupling level, impedance matching
length of tuning stub: matching
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Microstrip antenna arrays
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Microstrip antenna arrays
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Slot antennas
bi-directional radiation pattern
CPW feed line
easy to be integrated into antenna arrays and with active devices
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Slot antennas
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Slot antennas
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(Quasi-) Yagi-Uda antennas
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Quasi-Yagi antennas
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Quasi-Yagi antennas
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Other planar antennas
Frequency independent antennas (very wide bandwidth)
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V antenna linear tapered slot antennas (LTSA)
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Conclusions
For a good antenna design:
Understand the main antenna parameters
Start using simple analytic formulas
Optimize the antenna layout using electromagnetic
simulations and multiple parameter objective function
Test the antenna demonstrator before designing and
manufacturing complex front-ends
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References
C.A.Balanis, “ANTENNA THEORY – Analysis and Design”,
Second Edition, John Willey & Sons Inc., 1997
A.V. Raisanen, A.Lehto, “Radio Engineering for Wireless
Communication and Sensor Applications”, Artech House Inc.,
2003
T.A.Milligan, “Modern antenna design”, McGraw-Hill, 1985