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Antenna Products
Embedded/Internal Antenna Technology
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| Centurion invests heavily in R&D, conducting
multiple handset antennas research projects. Our research group
works closely with our customer projects groups and customers
to ensure that new development products will be in line with
our customers needs. Committed to bringing functional new technology
to our customers, we concurrently work with RF, mechanical design,
and production methods to reduce size and cost, and improve
RF functionality. |
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Market Trends
The handset market is perpetually
evolving. We have seen the shift from external retractable
antennas to stubby antennas, arriving ultimately at internal
antennas. Today's trends include:
- The prevailing implementation of internal antennas
over external antennas. CDMA system types are still
mainly external antenna applications.
- Integration of antennas into other components resulting
in cost reduction and improved functionality.
- Development of smaller antennas, which still meet
demanding performance goals.
- Enhancement of mobile phones functionality.
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Challenges in Terminal
Antenna Development
Terminal antenna design
is an art that is greatly dependent on the characteristics
of the mounting platform. This platform dependency presents
a substantial challenge to new terminal antenna development.
The variation in shape and construction of handset devices,
including bar and foldable mobile phones, dictates unique
behavior in every new terminal. In addition to designing
antennas and matching networks that optimize performance
for a given platform, Centurion applies extensive terminal
design knowledge to make optimal use of the antenna
solution.
Another aspect of effective terminal antenna design
is the antenna's sensitivity to the surrounding environment.
A terminal must function in a variety of situations,
whether in a chest pocket, on a table, or of course
close to the head. Great attention to detail and experience
is required during the design process to maintain optimal
performance in all defined user scenarios.
In most cases, a terminal antenna is a unique design
applying one of our well-proven production processes.
Centurion designs antennas for mass production with
production processes that conform to high quality demands.
We have an outstanding competence in these areas as
well as in the measurement of antennas in production. |
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RF Antenna Characterization
for Terminals
When characterizing an antenna
for usage on a wireless terminal, it is important to consider
three main characteristics:
- How well the antenna fits to transceiver impedance
- otherwise referred to as impedance mismatch. For
a given impedance, compatibility is quantified by
a number of different elements, such as Antenna Impedance,
Reflection Coefficient, Return Loss, and Voltage Standing
Wave Ratio (VSWR). We use a network analyzer to measure
these elements, and a Smith Chart to provide a visualization
of impedance mismatch.
- How well the antenna radiates, usually quantified
by Gain, Mean Effective Gain (MEG) or Efficiency.
We measure these elements in our state of the art
near or far field measurement chambers and simulation
tools.
- How well the antenna interacts with other objects.
A wireless terminal in use is most often close to
an object that will distort its operation. It is vital
to address these effects in the design work. Apart
from distorted operation, a terminal must also comply
with safety standards regarding electromagnetic power
absorption in the human body. We quantify power absorption
by measuring the Specific Absorption Rate (SAR) in
our state of the art SAR measurement chambers.
A great depth of experience is necessary to correctly
characterize a terminal antenna. This is true whether
measurements or simulations are used. Centurion has cultivated
a unique capability in this field. We perform accurate
antenna measurements in USA, Sweden and China, and are
compliant to relevant standards.
In our development work, we extensively use Electro Magnetic Simulation tools,
expediting new idea testing without the impediment of
building physical prototypes. Using this technology, we
can extract all parameters that characterize an antenna,
and visualize currents on the antenna and chassis, enabling
the exciting possibility of design improvement. In just
a few hours, a parameter scan can reveal vital information
on how a design is actually working.
Centurion uses a number of programs, and is highly proficient in these
programs. The programs rely on Finite Difference Time
Domain (FDTD), Finite Element Method (FEM) and Method
of Moments (MoM). |
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Antennas
Used on Terminals
Electrical Dipoles
Electrical dipole antennas are very popular within the
antenna community. They typically have a size that is
approximately half a wavelength. A dipole at this length
is purely resistive and has an antenna resistance of 73
W. At 900 MHz a half-wavelength is 0,15 m and at 1.8 GHz
0,075 m.
Due to these rather large sizes, half wavelength antennas
are seldom used at frequencies below 1 GHz for handheld
terminals. However, quarter wavelength dipole antennas
are popular. They form a first half of the half wavelength
antenna. The terminal's PCB provides the other half.
When a dipole is shorter than a half wavelength, it becomes
increasingly capacitive with decreasing antenna resistance.
The radiated field from an electrical dipole is linear
polarized.
Small Loops
The radiation behavior of a small loop, in free space
only, is comparable to a small electrical dipole. An electrical
dipole operated within close proximity to a user exhibits
decreased performance. However, when the loop is in operation
close to a user, it makes constructive use of the user's
body. Another difference between small loops and short
dipoles is that the impedance is reactive with a small
resistive part. These antennas are widely used in pagers,
with limited mobile phone application, so far.
Helical Antennas
Helical antennas are historically the most widely used
terminal antenna type. Electrically, they appear to be
a number of short dipoles with small loops positioned
in-between. The ingenious effect is that the capacitive
behavior of a short dipole is balanced by the inductive
behavior of a small loop. With the diameters used by terminal
antennas, the short dipoles will dominate the radiated
fields. One of the greatest disadvantages of helical antennas
is that it is complicated to achieve good multiband performance.
Sometimes two or four helices are intertwined. These antennas
are called bifilar and quadrifilar antennas and are popular
within space/satellite applications.
Helical antennas are often combined with a retractable
quarter wavelength whip, thus making it possible to have
both small size and improved performance by using a whip
when needed.
Meander Antennas
These antennas comprise one or more metallic traces that
meanders back and forth in the antenna. They are closely
related to helical antennas in that the inductive behavior
of the meander is balancing the capacitive properties
characteristic of a short dipole. However, the trace is
not making loops. Instead, it should be interpreted as
small sections of transmission lines with short dipoles
positioned in-between. In addition, in this case the radiated
field is dominated by the electrical dipoles. Compared
to helical antennas, meander antennas offer a greater
possibility to design antennas with multiband performance.
Centurion also uses this technology in conjunction with
foldable handsets. In which case, a flat meander antenna
is secured to the top of the lower foldable section.
Planar Internal Antennas
Due to the drive toward fitting antennas inside the terminals,
planar antennas have grown increasingly popular. A classical
planar antenna is the patch antenna. It is often a rectangular
metallic film mounted above a ground plane. However, a
patch antenna must be about a half wavelength in size,
which for most terminal applications is not permissible.
One popular method to reduce size is to use dielectrics
with a high dielectricity constant. This adds weight and
reduces the antenna bandwidth. For terminal applications,
almost only GPS applications currently use these antennas.
Another way to reduce size is to cleverly incorporate
grounding. By doing this, the added inductance to the
capacitive planar antenna shifts antenna resonance to
a lower frequency. Known as Planar Inverted F Antennas
(PIFA), the design of this group of antennas normally
includes some kind of slot, thus adding electrical length
to the antenna.
When designing antennas at frequencies above 1.7 GHz,
parasitic elements are popular. Consisting of a grounded
strip that runs parallel to the antenna, the effect of
these parasitic elements is upper band widening.
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Antennas 
