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Handset Antennas
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Antenna constraints for portable devices
1. electrical size. The antenna can be physically bounded by a spherehaving a radius equal to freespace/2. Planar inverted-F antennaswith shorting pins or/and slots are typical examples of this category.
2.physical size. An antenna which is not electrically small may featurea substantial size reduction in one dimension or plane. Microstrippatch antennas with ultra low profiles belong to this category.
3. function. An antenna which is not electrically or physically small insize may possess additional functions without any increase in size.Dielectric resonator antennas operating in multiple modes fit thisdefinition.
4. Miniaturization. Therefore, the miniaturization of antennas forportable devices can be carried out in various ways
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Technologies to
miniaturize the antennas
1.The design and optimization of antenna geometric/mechanicalstructures, in particular, the shape and orientation of the radiators,loading,as well as the feeding network. This is a conventionalapproach and most often employed in antenna design. Inverted-Fantennas, top-loaded dipole antennas, and slotted planar antennasall fall into this category.
2. The use of non-conducting material.Antennas loaded with ferriteor high-permittivity dielectric materials (for instance, ceramics) areexamples of this type of technology, as is the dielectric resonantantenna.
3. The application of special fabrication processes. The fabricationof printed circuit boards and low-temperature co-fired ceramics havemade co-planar and multiple-layer microstrip patch antennaspopular. Such technologies are conducive to the mass production ofminiaturized antennas at low cost.
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Handset antennas
mobile phones, camera
phones, personal digital
assistants, and any other
handheld devices
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Practical considerations
Margin on the link budget
shortcomings of the handset form Loss in the system
become critical when the user is in an area of marginal
network coverage or inside a building
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Design challenges
New services require higher data rates, increasing number of differentfacilities in the terminal puts great pressure on the available space forantennas.
Handset designers expect that multiple antennas can be operatedsuccessfully in close proximity to components such as cameras, flashunits, loudspeakers, batteries and the other hardware needed tosupport the growing capabilities of the terminal.
Design challenge posed by handset antennas is becoming more
critical as networks evolve to offer a wider range of services
Example - a pocket-sized mobile terminal to be able to deliver
telephony (potentially video telephony), high-speed data services,
location and navigation services, entertainment and more to come
in the future
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Performance Requirements Mean effective gainaverage of measured gain at sufficient points on a
surface around the handset, = 10 log10 , 0dbi
Efficiency total power radiated by the antenna/forward power
available at its terminal Bandwidth- must be sufficient to cover the cell bands
Radiation patterns - Omnidirectional
Polarization- Randomly oriented Elliptical
Total radiated powertotal power flowing in the handset when it is transmitting
Total isotropic sensitivity (TIS)input signal power which gives rise to specific
frame rate, maximum range that the handset can operate from abase stationwith given level of performance
Input return loss RL and voltage standing wave ratio (VSWR)
VSWR= (1+)/(1- ), RL= -20 log10
Passive test- testing antenna with matching network with external connection
Active test- base station simulator is used to set call to cell in anechoicchamber and measurement of TRP and TIS
Free-space, in-hand and head-position measurements
Specific absorption rate (SAR)Study of possible effects of electromagneticwaves from handset on body tissues, vary from tissue to tissue, and henceorgans. SAR limit for general public.
Hearing aid compatibilityminimized interaction between GSM module andaudio amplifier. Poor result may lead to unpleasant buzzing sound
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Design consideration
Handset Geometries
Antenna Position in the Handset
The Effect of the User Antenna Volume
Impedance Behavior of a Typical Antenna in the Low Band
Fields and Currents on Handsets
Managing the LengthBandwidth Relationship
The Effect on RF Efficiency on Other Components of the Handset
Loudspeakers, Cameras, Vibrators, Batteries
Electromagnetic Compatibility (EMC) Shielding
The Antenna Feed Circuit, The Groundplane
Specific Absorption Rate
Hearing Aid Compliance
Economic Considerations
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Handset Geometries
Barphones
Clamshell Phones
The Open
Clamshel l
The Closed
Clamshel l
Slider Handsets
Other Handset
Configurations
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Antenna position
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Antenna position-
Clamshell handset
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Antenna position-
Slider phone
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Electrically Small Antennas
Electrically small antennas are small compared to the
wavelength. Maximum dimension is less than /2.
Their performance are closely related to their electrical size. Theproduct of the bandwidth and the gain is a function of the size of the
antenna, so that the gain can only be increased at the expense of the
bandwidth, and vice versa.
An electrically small antenna are highly dependent on the
environment in which the antenna operates, which must be taken intoaccount. The environment comprises both the device on which the
antenna is mounted and the surroundings, mainly humans. Therefore, the
size of the device, the position of the antenna on it and the type of
antenna convenient for a given application
Efficiency and Extended Bandwidth
The Dimensions of the handset chassis The permitted size of
the antenna. behavior of small unbalanced antennas is strongly
dependent on the dimensions of the ground plane.
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Cl f H d t A t
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Classes of Handset Antennas
Whip antennas:
A quarter-wavelength whip or blade mounted on a largehandset provides efficiency Unfortunately low-band whips areinconvenient: they typically have to be extended or folded upwhen the phone is in use and the moving mechanical partsare costly and become worn or broken.
Meanders and coils:
To make whips more acceptable to users, the simple straightconductor is wound into a helix or meandered so the quarter-wave conductor is contained in a short housing, oftendesigned to be flexible.
Dual-band whips and coils:
Provides second tier of mobile services in the high bandsquickly led to requirements for dual-band handsets.
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Early internal antennas:
One of the earliest forms of internal antenna was a meandering conductoretched on the main printed circuit board (PCB), often configured as a form
of T or inverted-L antenna. The addition of shunt-feeding to the inverted-Lcreated the inverted-F antenna (IFA) which has become a classic standardform of internal antenna. In the planar inverted-F antenna (PIFA) the upperloading wire of the conventional inverted-F becomes a flat plate (Figure2.2(c)).
Dual-band internal antennas:
The frequency assignments for the low and high bands are about an octaveapart, so it is not easy to provide an acceptable input VSWR using a singleinternal element. The standard solution is to use two radiating elements fedin parallel at their common point.
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Triple-, quad- and penta-band antennas:
The growth of world-wide mobile services has seen a progressive increase in
the number of frequency bands that must be supported by a handset. For a
quad-band or penta-band antenna, the low-band response must range over
826960MHz (15.3%) and that of the high band over 17102170MHz(24%). These bandwidths far exceed those of the early dual-band antennas.
Multiple antennas:
Techniques such as dual-antenna interference cancellation (DAIC) requirethe provision of a second receiving antenna [17]. The challenge is to find
room for this second antenna and ensure that neither antenna is blocked by
the users hand. This requires a second broadband antenna.
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Multiple-input, multiple-output (MIMO) schemes:
These exploit multipath transmission to enhance the available data rate.Multiple signal samples are transmitted and the data stream is reassembledafter being received by multiple independent receiving antennas.
Other configurations:
At the upper end of the market, handsets are becoming ubiquitous terminalsfor communications, information and entertainment. This is drivingrequirements to add antennas capable of supporting GPS, WLAN,Bluetooth and DVB-H, VHF and later medium/high frequency digital radio,Band II analog FM, DAB (Digital Audio Broadcasting) and DRM (DigitalRadio Mondiale). The antenna designer must not only create new designscapable of providing these facilities but also manage the interactions thatcan limit their usefulness. This represents a major challenge.
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Optimized antennas
External Antennas
Off-Groundplane Antennas
On-Groundplane Antennas
Simp le Single-Band PIFAs
Mult i -Band PIFAs
Extended PIFAs
PIFAs w ith Parasit ic
Radiators
Dielectr ic-Excited PIFAs
Balanced Antennas
Off G d l A t
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Off-Ground plane Antennas
Dielectric-excited PIFA
multi-band configurations
Off-Groundplane Antennas
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Practical Design Approach
Literature survey and
Selection of antenna structure
Design of antenna
Generation of different geometry
If required
If design ofantenna
met specification
Theoretical investigation and computer
simulation of
antenna structure
Prototype fabrication, testing andMeasurement
Optimization of
antenna
parameters
Yes
No
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Process of designing Antenna
Evaluate the target specifications from customers, thedimensions and configuration of the handset,
Evaluate the local environment of the antenna relative toother components.
Following Design procedure by choosing potentialelectrical designs for the antenna by simulation andexperiment
Testing all the parameters of interest
Optimizing the antenna performance before finalizing thedesign to be embedded into the handset devices.