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INV ITEDP A P E R
Antennas in Cellular PhonesforMobile CommunicationsProgress in the design of mobile phone antennas during the past 15 years
is reviewed in this paper; a recent development on new antennas is
also described.
By Zhinong Ying, Senior Member IEEE
ABSTRACT | The mobile industry has experienced a dramatic
growth; it evolves from analog to digital 2G (GSM), then to high
date rate cellular wireless communication such as 3G (WCDMA),
and further to packet optimized 3.5G (HSPA) and 4G (LTE and
LTE advanced) systems. Today, the main design challenges of
mobile phone antenna are the requirements of small size, built-
in structure, and multisystems in multibands, including all cel-
lular 2G, 3G, 4G, and other noncellular radio-frequency (RF)
bands, and moreover the need for a nice appearance and
meeting all standards and requirements such as specific ab-
sorption rates (SARs), hearing aid compatibility (HAC), and over
the air (OTA). This paper gives an overview of some important
antenna designs and progress in mobile phones in the last
15 years, and presents the recent development on new antenna
technology for LTE and compact multiple-input–multiple-
output (MIMO) terminals.
KEYWORDS | Body effect; HAC; integrated antenna; LTE
antenna; MIMO antenna; mobile terminal antenna; multiband
small antenna; over-the-air (OTA) performance; SAR
I . INTRODUCTION
The cell mobile systems have evolved from analog systems,
called the first-generation (1G) systems, to digital systems,
called the second-generation (2G) systems, and further tothe third-generation (3G) systems, which are capable of
multimedia transmission. Now the 3G systems evolve to
the fourth-generation systems (LTE advanced) through
the, e.g., HSPA and LTE systems. In addition to the cellu-lar mobile phone systems, various wireless mobile systems
have been deployed and started services in various areas.
For example, multiband global navigation satellite system
(GNSS), multiband WiFi (2.4 and 5.2 GHz) and 60 GHz,
TV, FM radio, Bluetooth, near-field communications (NFC),
and ultrawideband (UWB) wireless systems. The operating
frequencies used by these systems range from kilohertz
regions to as high as gigahertz regions, depending on thesystem performance, complexity, transmitting media and
data, and so forth. The services of these systems range from
very short distances to intermediate distances, whereas
mobile phone systems provide the nationwide service. Va-
rious antenna systems have been developed for these mobile
systems and accordingly the antenna technology has made
progress along with the deployment of these systems.
The main challenges for the mobile terminal antennaare as follows: small size, built-in, multiband, and
coexistence of a multiradio system and a multiple-input–
multiple-output (MIMO) system. For example, a smart-
phone needs to support more than ten 4G and 3.5G
networks and all 2G and 3G networks for global coverage
and roaming, which means dozens of cellular radio-
frequency (RF) bands [see Fig. 1, third-generation
partnership project (3GPP) bands evolution] plus multi-antenna systems in some of the bands. There have been two
major trends in the antenna design. One is that antennas
for mobile terminal require small size, built-in, and
multiband operation with a nice appearance. Another is
that antennas for mobile terminals need to fulfill various
standardizations and requirements, depending on the func-
tion and complexity of the system, its service areas, the
quality and quantity of data to be transmitted, and so forth.For example, 3GPP and many of the mobile communication
network operators are introducing the requirements of the
RF over-the-air (OTA) performance of a mobile phone in
Manuscript received July 31, 2011; revised December 17, 2011; accepted
January 18, 2012. Date of publication March 16, 2012; date of current version
June 14, 2012.
The author is with the Network Research Laboratory, Research and Technology,
CTO Office, Sony Ericsson Mobile Communication AB, Lund 22188, Sweden
(e-mail: ying.zhinong@sonyericsson.com).
Digital Object Identifier: 10.1109/JPROC.2012.2186214
2286 Proceedings of the IEEE | Vol. 100, No. 7, July 2012 0018-9219/$31.00 �2012 IEEE
certain conditions with impact of user head and hand in
order to improve the network operation performance.
Another important issue to be considered in designing
antennas for a mobile phone is the reduction of specific
absorption rate (SAR) values which could be caused by RF
radiation from multiple radio and antennas in the mobile
phone. The SAR should be as low as possible, especiallywhen in contact with the human brain. The handset with
multiple transmitters and antennas will increase the com-
plexity of the near-field problem. In addition, hearing aid
compatibility (HAC) is required for mobile phones in some
countries, which will also increase the complexity of the
antenna design. For a compact mobile terminal, environ-
mental conditions are also a serious issue to be considered
in the antenna design. Proximity effects due to materialsnear the antenna element, such as circuit components,
acoustic components, camera, print circuit board ground-
ing quality, may degrade antenna performance. In modern
antenna design, the proximity effect is treated with integ-
ration concept, in which nearby materials are included in
an antenna system as an integral part of the radiator.
For MIMO and diversity application in WiFi, 3.5G, and
4G systems, the multiantenna system requires low mutualcoupling loss and low pattern correlation between an-
tennas in order to realize good diversity or MIMO perfor-
mance. The channel impact is not only path loss, but also
signal transmission rate, bandwidth, delay spread, and
Doppler shift in the Rayleigh fading environments. These
parameters are particularly important in the digital modu-
lation systems used in high data-rate transmission.
In this paper, the author will only discuss some built-inmultiband cellular antenna designs in mobile communi-
cation handsets including SAR, human body effect issues,
and the recent compact MIMO antenna technology for
mobile terminals due to the limited space.
II . MULTIBAND BUILT-INANTENNA DESIGN
A. Antenna TypesSmall antenna types can be classified according to their
geometry: dipoles, slots, and cavities. More complex geom-
etries can be developed from these fundamental antenna
types. The simplest omnidirectional type of the antennais the dipole. The external antenna or the internal
antenna which is free from ground plane on a mobile
terminal can be considered as an unbalanced dipole.
Usually, we call it a monopole antenna, because the an-
tenna element is much smaller than the actual handset
chassis size. Slot antennas, also called magnetic dipoles,
can be seen from a long, narrow opening on a metallic
surface. The planar inverted-F antenna (PIFA) andinverted-F antenna (IFA) can be considered as a mixed
dipole and slot antenna. The cavity antenna in its simplest
cases can be a patch antenna, or a dielectric resonator
antenna (DRA) [1].
Before 1998, most of the mobile phones used the ex-
ternal antenna, which is simple and easy to reuse. The
most popular design was the dual-band nonuniform helical
antenna proposed by Ying [2]. The helix had quarterwavelengths at the low band functioning as a quarter wave
monopole, and it had a nonuniform pitch angle or diam-
eter to control the second resonance frequency band. The
antenna had a high efficiency and was cheap to manufac-
ture and it has been used in over a billion mobile phones
worldwide.
B. Multiband Internal Antenna DesignThe internal antenna can increase the mechanical
robustness of a mobile terminal, and the internal antenna
housing can also be used as an acoustic cavity to improve
the audio performance. It has followed the trend of the
mobile phone to become a multimedia mobile handset
since the late 1990s. These factors have led to a market
acceptance worldwide.
The main types of internal antennas for stick-typehandsets are the PIFA [3], the folded monopole antenna
[4], and the loop antenna [12], [13]. The PIFA is usually on
a ground plane, and may have a feeding pin and several
ground pins. The radiation pattern is affected by the
ground plane, and can be directive, especially in the high-
frequency range. Fig. 2 shows an example of a mobile
phone equipped with an internal PIFA in 2000. The an-
tenna is located at the top of the phone behind theprinted wire board (PWB). On the other hand, the folded
monopole antennas are usually used at the bottom of the
handset to have less head loss and risk of high SAR.
In 1997, Hall first proposed a PIFA composed of two
separate patches of different sizes to achieve dual-band
performance [5]. The initial idea of a common feed for a
dual-band PIFA was mentioned and later a lot of work was
done to realize it for cellular application. Between 1997and 1999, several dual-band PIFAs based on a slot cutting
patch were developed in the mobile phone industry, and a
lot of work was later published [6]–[9]. The antenna
bandwidth depends on the antenna size and ground plane
size. A PIFA on a bar phone has the maximum bandwidth
with 120 mm for the 900-MHz band and 80- or 140-mm
PCB length for the 1800-MHz band.
Fig. 1. 3GPP cellular RF bands with different standards evolution.
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To meet the multiband application, some slot cutting
designs were developed. Some PIFA variants in the mobile
terminal applications are shown in Fig. 3. A PIFA with one
slot has dual resonance, mainly used in dual-band appli-
cations. A PIFA with two slots (one slot is between feeding
and grounding posts) can have an extra resonance at the
high band. A PIFA with a parasitic element can have anextra resonance at the high band [8]. All of those three
antennas have been very popular solutions in the handset
applications. The compact multiband phone in Fig. 2 was
equipped with the internal antenna design in Fig. 3(c).
The mentioned branched monopole antenna can be
built with a very low profile form. Then, it is possible to
make it integrated with the housing of a mobile terminal.
The design of the antenna is similar to the external mono-pole antenna and can be found in many references today
[6]–[9]. The bandwidth of the monopole is much larger
than a PIFA; the monopole can be capacitive, coupled, or
matched to the terminal housing to excite the chassis mode
to gain some extra bandwidth when the chassis length is
larger than a quarter wavelength. The first systematic ana-
lysis work about bandwidth enhancement by using the
chassis mode of the mobile handset was done byVainikainen’s group [10], [11]. When the height of the
low-profile monopole is too low, the antenna becomes ca-
pacitive, an extra ground pin is needed to form a matching
loop, and the antenna becomes a branch IFA or non-
grounding PIFA [6]–[9]. The monopole or ground-free
PIFA could be designed with very small thickness, and
could become a very popular antenna solution for slimmobile phones.
A loop antenna (usually one end is the feed and another
end is grounded) has a multiband feature due to the
multimode of the loop trace. It could be designed both on
ground or as a nongrounding type. The high-band reso-
nances could be merged to be able to cover a wide fre-
quency range. Due to the coupling between different
sections of the loop, the loop antenna has better bandwidththan PIFA and possibly less hand effect. It becomes a very
useful design in mobile phone applications [12], [13].
C. Bandwidth-Enhanced AntennasIt was discovered that the patch antenna bandwidth
can be enhanced by introducing a distributed capacitive
coupling feed in the antenna with an optimized design
[14]. The dual resonance feature was found in both the low
band and the high band by combining the feeding element
resonance and the resonances of passive element and
chassis. A dual-layer coupling fed multiband antenna wasinvented and used in mobile phone application in 2001
[15]. Later the design was developed further to a single-
layer design and LC loading design [16], [18]. High dielec-
tric material was introduced to the c-fed antenna to make it
compact and less sensitive to human body [17]. The c-fed
concept was applied to the ground-free-type antenna, and
the bandwidth was enhanced dramatically. Wong’s group
has conducted a lot of work, which attracted interests fromthe industry [18]–[22]. Fig. 4 shows an example of engi-
neering sample based on a c-fed ground-free antenna with
LC loading and the bandwidth performance of such an
antenna on a 46 � 96 mm2 small ground plane [22]. The c-fed antenna design concept built in PWB was sold by some
of the antenna vender as Bmetamaterial antenna[ [23]. In
that design, the c-fed structure is equivalent to one cell of
Fig. 2. A small handset with an internal multiband PIFA in 2000.
Fig. 3. Summary of slot cutting PIFAs. (a) A PIFA with one slot has
dual resonant. (b) A PIFA with multislots (one slot is between feeding
and grounding posts) can have extra resonant at high band. (c) A PIFA
with a parasitic element can have extra resonant at high band.
Fig. 4. The engineering sample (10 � 5 � 45 mm3) of the c-fed
monopole with LC loading [22], and the reflect coefficient of the
antenna in 110 � 50 mm2 phone chassis in free space and close to the
humanhead; it haswide band coverage (700–960 and 1710–2170MHz)
with a compact antenna size.
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2288 Proceedings of the IEEE | Vol. 100, No. 7, July 2012
the structure of metamaterial, which results in a lot ofpublic interests. The c-fed design was extended to a com-
bination of a compact ultrawideband antenna and parasitic
element which is connected to a small ground plane. The
bandwidth of the antenna could cover from few hundred
megahertz to over 10 GHz [24], [25].
III . COMPACT MIMO ANTENNA DESIGNFOR HSPA AND LTE MOBILE TERMINALS
A. Some Important Characterizing ParametersRecently, HSPA (3.5G) and LTE (4G) mobile systems
have been deployed worldwide to support high-speed data
communication in the cellular system. The compact MIMO
and diversity antenna design is essential to such terminals.
To be able to characterize the performance of a compactMIMO antenna in a mobile environment, some parameters
were used or newly defined. The mean effective gain
(MEG) is a statistical measure of antenna gain in the mobile
environment. In MEG computation, the incoming wave
propagation model is defined to describe a specific mobile
environment. The correlation coefficient of the antennas is
another important parameter to describe the pattern
correlation between the antennas. These parameters canbe calculated from the 3-D far-field complex radiation pat-
terns of the antennas, which can be obtained from a nume-
rical method or an advanced measurement system. The
detailed definition could be found in the early literature
[26], [27].
According to the Shannon capacity theory, the capacity
is linearly proportional to the signal-to-noise ratio (SNR)
for low SNR cases and logarithmically proportional to theSNR for high SNR cases. So for a weaker signal and strong
fading case, diversity scheme is usually used. The effective-
ness of diversity is usually presented in terms of the diver-
sity gain (DG). The DG can be defined as the improvement
in time-averaged SNR of a combined signal from a diversity
antenna system, relative to the SNR from one single anten-
na in the system, preferably the best one. This definition is
conditioned by the probability that the SNR is above areference level. The detailed description can be found in
[28]. An effective diversity gain (EDG) is defined to include
the total antenna efficiency EDG ¼ DG � �ant, where �ant is
the antenna efficiency of the best antenna, including reflec-
tion losses, ohmic losses, and mutual coupling losses [28].
For a good signal and strong fading cases, MIMO
scheme is usually applied. The MIMO capacity is widely
accepted in communication domain to characterize theperformance of MIMO systems. They are not uniquely
defined. For example, capacity (in bits per second per
hertz) is calculated based on a reference SNR value (e.g.,
10 and 20 dB). The lack of universal reference values for
the outage probability level and SNR complicates the use
of these metrics for comparison between different MIMO
antennas. Recently, the multiplexing efficiency for MIMO
antenna has been defined [29]. The multiplexing efficiencyof a given M-element MIMO antenna can be defined as the
SNR required by the ideal M�M independent and iden-
tically distributed (i.i.d.) in the Rayleigh case to achieve an
ergodic capacity minus the required SNR to achieve the
same ergodic capacity for the MIMO antenna under test
[29]. For high SNR case, the multiplexing efficiency re-
duces to the closed form [29]
�mux ¼YMi¼1
�i
! 1M
detðRÞ ¼ �gdetðRÞ (1)
where �g is the geometric mean of the antenna efficien-
cies, �i is the total efficiency of the ith antenna element,
R has diagonal values of 1, and ½R�ij is the complex correla-
tion between the 3-D radiation patterns of antennas i and j.It turns out that, for two-element antennas, this metric has
been found to converge at a relatively modest SNR value of20 dB for the i.i.d. case. It is observed in (1) that �mux
consists of the geometric mean of the antenna efficiency, as
well as the loss of efficiency due to correlation between the
antennas. In the 2 � 2 MIMO case, the multiplexing
efficiency could be simply expressed as
�mux ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi�1�2ð1 � �eÞ
p(2)
where �1 and �z are the total efficiency of antennas 1 and 2,
including reflection losses, ohmic losses, and mutual
coupling losses; and �e is the envelop correlation betweenantennas 1 and 2. From the equation, it was found that the
MIMO gain depends mainly on the total antenna effi-
ciency of the antenna elements when the envelop correla-
tion between the antenna elements is below 0.5, and the
correlation has significant impact on MIMO gain when the
correlation is high [29].
B. Decoupling and Decorrelation of CompactMIMO Antennas
To realize a good compact MIMO antenna, the antenna
system needs low coupling loss and low correlation ac-
cording to (2). Several different methods have been pro-
posed to reduce the coupling and pattern correlation
between antennas [30]–[46]. The most effective decou-
pling method is to design the orthogonal mode antenna,
e.g., the three-port DRA proposed by Ying [34], [35]. It hasmore than 15-dB isolation, over 80% efficiency, and very
low correlation, and has a very good diversity and MIMO
performance. Fig. 5 shows the comparison of the MIMO
throughput of WiFi 11n (which has similar frequency range
in LTE band 7) by using a typical three-port DRA antenna
and conventional three dipoles. The orthogonal mode
could also be realized by combining the electric dipole and
Ying: Antennas in Cellular Phones for Mobile Communications
Vol. 100, No. 7, July 2012 | Proceedings of the IEEE 2289
the magnetic dipole such as loop or slot antennas [37],
[38]. The bandwidth of the orthogonal mode antenna is
limited by the bandwidth of the antenna resonant modesand the antenna size. The principle was used even for
cellular low band between 700 and 960 MHz by using the
orthogonal property of the loop antenna and the dipole
antenna [36].
Another way to reduce coupling is to use the parasitic
scatter. The scatter could be realized by chokes, parasitic
stub, and modification of the ground plane by notches and
slots [39], [40]. With the scattering of the structure be-tween the MIMO antennas, the isolation could be im-
proved and correlation will be low. The bandwidth is
limited by the size of the MIMO antenna array [39]. The
engineering scatter solution by using decorrelation wave
traps for the LTE cellular phone was proposed [41].
Closed space antennas have strong scattering effects.
The scattering and coupling could be well controlled to
reduce the pattern correlation of the compact MIMO an-tenna and have good antenna efficiency and bandwidth. A
wide colocated MIMO antenna has been recently proposed
for the multiband LTE mobile handset based on this design
concept [42].
Neutralization line, hybrid coupler, and lumped LCmatching network are also effective ways to reduce mutual
coupling and correlation.
1) A neutralization line is a metal strip that connectsthe two antennas. The line allows currents to in-
teract between the antenna elements, thus result-
ing in reduced coupling at a certain frequency.
This technique has proven good with PIFA and
monopole antennas around 2 GHz by Luxey [30].
One of the advantages of this design is that the
decoupling element could be a part of the antenna.
The industry products based on this concept havebeen used in the high-band MIMO system [43].
The bandwidth of this design is limited by the size
of the antenna array. Recently, an investigation
has been done for the 700-MHz LTE terminal
based on this method [44]. The bandwidth was
very small.
2) The 90� hybrid coupler is a standard componentin the microwave design, used to both separate
and combine signals in RF applications. The sig-
nals at the output ports are 180� separated from
each other, but relative to the input port the phase
shift is �90 � (balanced output), which results in a
good isolation between the antennas [43].
3) The 180� coupler can be used in a couple of dif-
ferent ways, mainly for splitting or combiningsignals. The four-port network could realize the
input ports have one even mode and one odd
mode, thus the two ports are decoupled. In this
case, the two ports are not symmetric, the common
mode has nearly the same pattern as the single-
port antenna, and the differential mode has
narrowband, which depends on the size of the
array antenna [43].The miniaturization of impedance control circuit
methods mentioned above could be achieved by an equiv-
alent circuit of lumped elements. The topologies could be
found in the early literature. In [43], some comparison
works were performed. We took a simple model of two
monopoles of 0:1� spacing over a large ground plane, as
shown in Fig. 6(a). Due to the mutual coupling, the radia-
tion efficiency drops to about 55%. With the neutralizationline it could be improved to 75%. With the coupler and
lamped circuit network it could improve over 90% with a
limited bandwidth [43].
The bandwidths of different decoupling techniques
such as the neutralization line, the 90� hybrid coupler, the
180� coupler and their equivalent LC circuits, and
Fig. 5 Measured throughputs of the WiFi terminal with compact
MIMO DRA antenna and dipoles.
Fig. 6. The decoupling network based on the 180� coupler:
(a) two closed monopoles with 0:1�; (b) decoupling network;
and (c) S-parameters.
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2290 Proceedings of the IEEE | Vol. 100, No. 7, July 2012
matching networks have been studied [43]. It shows thatthe bandwidth of the decoupling is mainly limited by the
size of the antenna array. Even though the coupler or the
network has a wide bandwidth, the compact MIMO an-
tenna has only limited uncoupled bandwidth due to the
physical constraint. However, for the 180� coupler case, it
has an even mode at port1 and an odd mode at port2. The
even mode ðS11Þ is observed to give significantly larger
bandwidth than the odd mode ðS22Þ. The coupling andpattern correlation is extremely low. Fig. 6(c) shows the S-
parameters by using the equivalent circuits of the 180�
coupler. The even mode ðS11Þ is observed to give signifi-
cantly larger bandwidth than the odd mode ðS22Þ, which
implies that the approach may be suitable for systems (e.g.,
LTE) that only require the MIMO operation in the down-
link. Unfortunately, the insertion loss of the lumped cir-
cuit in this case could be rather high [43].The microwave coupler decoupling has been investi-
gated recently for the multiband LTE mobile terminal in
the 700–960-MHz range [45]. It shows that it works well
within the limited bandwidth.
For the mobile phone case, good MIMO and diversity
performance could be achieved by pattern diversity when
the frequency band is around 2 GHz or above. But a do-
minant coupling utilization occurs when more than oneantenna element efficiently exploits the ground plane as a
radiator especially for the low bands between 700 and
960 MHz [46], [47]. A detailed parametric study has been
performed based on the insight gained from the charac-
teristic mode analysis and the results indicate that isolation
can be improved by optimizing both the antenna type and
the antenna location, i.e., only one of the antennas uses the
chassis mode and the other antenna uses the localizedmode. It is confirmed that both capacity and diversity
performance for a given bandwidth can be improved using
this simple approach. The localized mode antenna could be
realized by using more directive antennas such as patch,
notch, and balanced dipoles. One significant advantage of
this approach is that no additional (and inherently lossy)
lumped element or matching circuit(s) is required to
achieve better MIMO performance [46].
C. Antenna and MIMO ChannelThe mean effective gain of the mobile phone antenna
depends on both the antenna pattern and the propagation
channel. The antenna system performance in multiple
path environments depends on both the antenna perfor-
mance and channels.
1) For the diversity case, it was found that the EDG ismainly determined by the signal correlation,
signal imbalance, and diversity combining
method, while DG includes the effects of antenna
matching, losses, and mutual coupling. It was
found that the parameters such as correlation and
apparent DGs do not depend strongly on the
various average propagation models [48]. Thus,
the isotropic random environment seems to be a
good simplified scenario to evaluate the diversity
performance.
2) For the LTE MIMO case, the mean effective gain
and the correlation will determine the MIMOperformance. Inside a typical smartphone, the
antennas have quite low correlation for the fre-
quency bands around 2 GHz and above. So the
main effort to realize good MIMO performance is
to design highly efficient antennas with less cou-
pling loss at those frequency ranges. However, it is
quite a big challenge to design the low correlation
and low coupling antenna at low band, especiallyat the 700-MHz band. Some detailed mockups in
different correlation levels were built and tested
at the Sony Ericsson research laboratory and dur-
ing a field trial with Ericsson Research. Fig. 7
shows four different MIMO antenna designs for a
smartphone at the 700-MHz band. The design
shown in Fig. 7(a) has two monopoles at both
ends, where the chassis mode is strong and thecorrelation is rather high. The design in Fig. 7(b)
has one monopole and one notch. The antennas
are orthogonal to each other, and correlation be-
comes lower. The design in Fig. 7(c) has the colo-
cated loop antenna, where one antenna element is
fed by two port; it is a design for very high
correlation on purpose. The design in Fig. 7(d) has
one chassis mode monopole and one localizedmode patch antenna. The correlation is extremely
low. The mockups were tested and characterized
in the Sony Ericsson laboratory. The perfor-
mances are summarized in Table 1.
Comparing with the performance of reference
antenna orthogonal dipoles, it was found that the
mobile terminals with the compact MIMO
antenna arrangement could have fairly goodMIMO performance when the envelope correla-
tion is less than 0.5, even at the 700-MHz band.
Good antenna efficiency of both antennas is
Fig. 7. Different LTE antenna designs in a mobile phone at the
700-MHz bands. (a) Two monopoles. (b) Monopole and notch.
(c) Colocated loop. (d) Monopole and patch.
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essential to cover larger service area of LTE with
good data communication quality [49], [50].
From the field trial, it was also found that the MIMO
performance depends on the local dynamic channels. Withadaptive matching and beamforming of the MIMO an-
tenna, the throughput performance could be improved; the
research on this topic is ongoing [51], [63].
D. Multiband and Multistandard AntennaFront–End Architectures
As mentioned in the introduction, the mobile phone
antenna has to meet multiband and multistandard radiorequirements. The antenna has to be wideband or multi-
band and has to be designed in different RF architectures
to meet different requirements, e.g., carrier aggregations.
It is obvious that a flexible and cognitive RF front–end
technology will become very important to a future mobile
phone. The discussion on this technology is out of the
scope of this paper.
IV. STANDARDS AND INDUSTRYREQUIREMENTS
A. SAR and HACSAR is a value measuring how much power is absorbed
in a biological tissue when the body is exposed to the
electromagnetic radiation. The units are watts per kilo-gram of tissue elements. The maximum SAR is specified as
applying to any 1- and 10-g tissue elements. Governments
around the world have agreed to define the guidelines
concerning SAR limits. In Europe, the International Com-
mission on Non-Ionizing Radiation Protection (ICNIRP)
organization has set the SAR limit as 2.0 W/kg over a 10-g
cube. In the United States, the limit is 1.6 W/kg over a 1-g
cube according to the Federal Communication Commis-sion (FCC) [52]. Spatial-peak SAR is defined as the maxi-
mum average SAR of a 10- or a 1-g cubic volume of tissue.
SAR is measured on a completely head or flat phantom
placed next to the mobile phone and the highest value
detected decides how large the SAR value is. The mea-
surements are made on a biology-simulating liquid, which
has a relative permittivity and a conductivity that depends
on the frequency. The detail standard could be found in the
literature [7], [8], [52].
Mobile phones interfere with hearing aids both by their
RF emission and their electromagnetic (EM) field. Modernhearing devices have an audio amplifier, which makes it
easy for hearing aid users to use an ordinary phone. If the
hearing aid is in a high level pulsed EM signal such as the
talking position of the mobile phone, the amplifier will
generate some unpleasant buzzing noise. HAC is defined
as the highest E-field and the highest H-field detected in
the near-field area. The details of the measurement
method can be found on the FCC’s website [53]. SAR andHAC can also be predicted by using numerical methods
such as finite differential time domain (FDTD) or finite
element method (FEM) [7], [8], [52].
It is observed that exposure to magnetic fields (electric
currents of the radiator) rather than electric fields leads to
a high value of SAR in the body. So the antenna type,
antenna position, phone style, material loading, and metal
grounding will influence the SAR values. In order torealize lower SAR in the brain tissue, in general the
ground-free antenna has to be placed at the bottom of the
mobile phone and on-ground antenna such as PIFA could
be placed at the back of the PWB of the phone to minimize
SAR. Since it is a near-field problem, the detailed solution
depends on the individual antenna design, grounding, and
nearby components [56].
In practical cases, SAR and HAC are caused by the nearfield which not only depends on the antenna type and po-
sition, antenna efficiency, and phone factor, but also on the
load pull of source impedance of the RF power amplifier [7],
[8], [56]. This will increase the uncertainty of the prediction.
Recently, the new challenges for the near-field issue in
a mobile phone handset were born from the RF multi-
transmitters in MIMO and multiband, such as how to ar-
range and control the antenna elements and how to designthe slim handset while still meeting safety limits. MIMO
such as LTE and WiFi will introduce multiradio transmit-
ters and multiantennas in a compact terminal. The body
tissue property such as the conductivity and permittivity
are frequency dependent, which increases the complexity
of the SAR problem. The research on minimizing SAR and
HAC such as the antenna types, the antenna arrangement,
Table 1 The Measured MIMO Antenna Performance of Four Different Mockups, and the Field Trial Test Results
Ying: Antennas in Cellular Phones for Mobile Communications
2292 Proceedings of the IEEE | Vol. 100, No. 7, July 2012
and the smart adaptive control RF architecture in themobile terminal is ongoing [54], [55], and to shorten the
SAR evaluation for the handset with multiple transmitters
and antennas, FCC has proposed the simplified test
method [58].
B. System OTA Performance and Body Impact onOTA Performance
The 3GPP has been working on the system require-ments and regulations of a mobile terminal for several
years. The test regulations on different standards were de-
veloped or are ongoing. The Cellular Telecommunications
and Internet Association (CTIA)/The Wireless Association
is a United States-based international organization that
serves the interests of the wireless industry by lobbying
government agencies and assists with regulation settings. A
working group, including operators, mobile phone manu-facturers, and test equipment vendors, is developing a
detailed test plan that includes LTE OTA test. The most
recent release of this plan can be found in [60]. According
to the test plan, the total radiated power (TRP) and the total
isotropic sensitivity (TIS) are obtained by full sphere
radiated measurements in an anechoic chamber for 2G and
3G mobile terminals. The test setup includes a base station
emulator which is used to establish a call to the mobilephone inside the anechoic environment. For transmitting,
the mobile’s effective isotropic radiated power (EIRP) can
be recorded as a function of the direction of radiation using
a narrowband power measurement device. For receiving,
the base station emulator is used to record the receiver
sensitivity as a function of the angle of arrival. Integration
of the EIRP and the sensitivity over the full sphere yields
the TRP and TIS, respectively. The test conditions thatinclude a human head and hand phantom are also defined.
It was found that the radiation from a mobile terminal
is from both the antenna element and the terminal chassis.
It is very important to measure the final radiation perfor-
mance that influences the human body. The body absorp-
tion can be defined as head loss and hand loss when the
handset is in a talking or browsing position. CTIA has
proposed several body test cases for a mobile phone. Therequirements are under discussion for passive and active
modes. A phantom equivalent to the human body tissue is
usually used to do the test. A typical head phantom is the
specific anthropomorphic mannequin (SAM) phantom
which is defined for SAR measurement. The hand
phantoms are defined for talking and browsing modes in
evaluating the effects on different phone factors [57],
such as mono-block phone (width is less than 56 mm),clamshell phone, and personal digital assistant (PDA)
phone (width is larger than 56 mm). Fig. 8 shows the test
case for a typical mono-block phone which has 45 mm in
width and 12 mm in thickness. The body loss depends on
the antenna design, phone size and thickness, and antenna
arrangement. There is no simple solution to all the
problems.
Systematic studies of body loss of the mobile phones
with different phone size, different antenna types, and
locations have been performed at the Sony EricssonResearch Laboratory [59]. It was found that body losses
strongly depend on the antenna location, type, phone
factor size, etc. For example the bottom mount monopole
antenna and the top mount PIFA antenna were built in a
stick phone as shown in Fig. 8 and both cases were studied
individually. Fig. 9 shows the body loss analysis results of
cases (b)–(d) in the 900-MHz band. It was found that in
the low band and the talking position with the hand thePIFA antenna had advantages with 4-dB less body loss for
a large phone factor. Fig. 10 shows the body loss of
cases (b)–(d) in the 1900-MHz band. It was found that
in the high band and the talking position with the hand the
top PIFA antenna had advantages with 3-dB less body loss
in general. These results are only valid for a feature phone
(width less than 56 mm). It was found that the smartphone
(width more than 56 mm) with PDA hand had totallydifferent features, and the relevant study was performed
recently [62].
For LTE and diversity application in a handset, the
body will usually reduce the pattern correlation. The
Fig. 8. CTIA-defined four different test positions: (a) free space;
(b) talking position; (c) talking position with hand; (d) browsingmode.
Fig. 9. Body loss analysis of a bar phone with the top PIFA and
bottommonopole in the 900-MHz band.
Ying: Antennas in Cellular Phones for Mobile Communications
Vol. 100, No. 7, July 2012 | Proceedings of the IEEE 2293
performance will drop due to the body loss and mismatch-
ing [47], [62]. The work of adaptive matching and adaptive
control of distributed MIMO antennas is a promising solu-tion to overcome human body detuning and loading [51],
[63]. The OTA measurement technology for LTE is under
study and will be proposed in the near future [61].
V. CONCLUSION
In this paper, the major challenges of the mobile handset
antenna for communication were addressed. Some impor-tant multiband internal antenna technologies in mobile
industry were reviewed. The mobile handset antennas
need to be small in size; built-in to meet multiband,
MIMO, and multistandard RF coexistence requirements;and fulfilling all standards and industry requirements with
a nice appearance. The recent research work of compact
MIMO antennas includes different decoupling techniques
such as the orthogonal mode, the localized mode, parasitic
scatter, and impedance coupler, which were also dis-
cussed. The decoupling bandwidth is limited by size of the
MIMO antenna array. For the multiband decoupling, the
use of the optimal design of hybrid decoupling techniquesor reconfigurable structures is required. The newly defined
MIMO antenna multiplexing efficiency was described,
which simply showed the relation of the MIMO perfor-
mance and the efficiencies, and the correlation of the
antenna elements. The practical issues of the human body
impact, SAR, and HAC with single and multitransmitter
were described and discussed, and the related research is
ongoing. Due to the small size, integration, multiband, andmultistandard requirements and human body effects, the
antenna design of the mobile phone is always the art of
compromising between the size, the phone appearance,
and the performance. The future research will focus on the
optimization of the MIMO, multiband, and reconfigurable
multiantenna system to reduce the human body impact
and enhance communication performances. h
Acknowledgment
The author would like to thank Dr. B. K. Lau’s group at
the Lund University, Lund, Sweden, and Prof. S. He’s
group at the Royal Institute of Technology, Stockholm,Sweden, for collaborative work. He would also like to
thank Dr. P. Karlsson of Sony Ericsson Mobile Commu-
nications AB for his helpful comments.
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ABOUT THE AUTHOR
Zhining Ying (Senior Member, IEEE) received the
B.S. degree from Zhejiang Normal University,
Jinhua, China, in 1982, the M.S. degree in electrical
engineering from Beijing University of Posts and
Telecommunications, Beijing, China, in 1986, and
did Ph.D. study at Chalmers University of Tech-
nology, Chalmers, Sweden, during 1992–1995 and
got the Licentiate degree.
He is an expert of antenna technology at the
Network Research Laboratory, Sony Ericsson Mo-
bile Communication AB, Lund, Sweden. He joined Ericsson AB in 1995. He
became Senior Specialist in 1997 and Expert in 2003. He has been guest
professor at Zhejiang University, China, since 2002. His main research
interests are small antennas, broad and multiband antenna, multichannel
antenna (MIMO) system, near-field and human body effects, and mea-
surement techniques. He has authored and coauthored over 80 papers in
various journal, conference, and industry publications. He holds more
than 70 patents andmore are pending in the antenna andmobile terminal
areas. He contributed a book chapter to the well-known Mobile Antenna
Systems Handbook (Reading, MA: Artech House, H. Fujimoto, Ed., 3rd ed.).
He had invented and designed various types of multiband antennas and
compact MIMO antennas for the mobile industry. One of his contributions
in the 1990s is the development of nonuniform helical antenna. The
innovative designs are widely used in mobile terminal industry. His
patented designs have reached a commercial penetration of more than
several hundred million products worldwide.
Mr. Ying received the Best Invention Award at Ericsson Mobile in 1996
and the Key Performer Award at Sony Ericsson in 2002. He was
nominated for the President Award at Sony Ericsson in 2004 for his
innovative contributions. He served as the Technical Program Committee
(TPC) Co-Chairman at the 2007 International Symposium on Antenna
Technology (iWAT), and served as session organizer of several interna-
tional conferences including the IEEE Antennas and Propagation Society,
and a reviewer for several academic journals. He was a member of the
scientific board in the European 6th Framework Program of the Antenna
Centre of Excellence (ACE) from 2004 to 2007.
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2296 Proceedings of the IEEE | Vol. 100, No. 7, July 2012
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