Novel Wideband MIMO Antennas that can cover
the whole LTE spectrum in Handsets and Portable
Computers
Customers’ increasing expectations for speed,
bandwidth, and global access is driving the evolution
of wireless broadband technology. Customers want
more information, such as business and
consumer applications, and entertainment available
through their mobile devices, but with greater
speeds[1]. LTE represents the next big step toward
the 4th generation (4G) of radio technologies which
expected to increase the capacity and speed of
mobile telephone networks. These expectations put a
significant burden on device performance.
The antenna is becoming an increasingly critical
component for LTE device vendors, In order to meet
the requirements of expanded, high cell capacity
data rates, multiple antenna configurations (MIMO)
specified for LTE mobile devices as smart phones,
tablets and notebooks. It is possible that a future
terminal device will have more than 20 antennas to
cover all the important wireless applications [2], in
addition the industry is painfully aware of the issues
that surround implementing LTE in small mobile
devices with already limited space and extremely
high performance expectations. Due to this trend,
wideband coverage is a hot issue that has to be
addressed [3].
The latest GSMA’s wireless intelligence report,
predicts that there will be 38 different spectrum
frequency combinations used in LTE deployments
by 2015. The lack of spectrum harmonization
represents a key challenge for the emerging LTE
ecosystem, potentially preventing vendors from
delivering globally compatible LTE products such as
devices and chipsets. Spectrum fragmentation has
the potential to hinder global LTE roaming if device
manufacturers are required to include support for
many disparate frequencies in their devices [4].
To satisfy the end user expectation of a global
LTE experience, the FDD/TDD dual mode device
is highly preferred and a universal RF chipset that
supports all global LTE bands should be required[5].
Thus, a compatible wide band LTE antenna is
absolutely needed.
Device makers are finding it difficult to decide
which bands to prioritize as chipsets and handsets
are developed. The priority is the 800 megahertz
band. Most of the investment has been directed
towards that because it is the band that two-thirds of
current LTE users occupy, largely driven by the US
network roll outs of Verizon Wireless and AT&T
[6]. This low frequency band means larger antennas
in terms of size, which is a challenging issue keeping
in mind limited size of LTE devices. However, in
Europe and even more so in the Asia-Pacific region
there are a greater number of LTE bands and
combinations to be addressed.
The roaming point is a critical one because operators
are targeting LTE towards their high value
customers, in the initial stages of the market. Those,
by definition, are business users with the propensity
to roam. Yet, in fragmented regional markets such as
Europe, LTE roaming is some way off as operators
will be providing LTE in different bands and devices
will need to be able to seamlessly switch between
the frequency bands used for LTE in addition to the
2G and 3G networks[6].
What is clear is that in order to service the high
spending, first wave of LTE users some form of
roaming between LTE spectrum bands and the 2G
and 3G networks will be required. It seems illogical
that operators will sell the benefits of LTE in their
home markets but, as soon as the high spending LTE
customer changes country, they will only be offered
2G or 3G service. For operators, a world LTE device
at a keen price point is needed — but it remains
some time away from appearing in the market [6].
The bigger issue is that operators are running out of
3G capacity. They need handsets so they can migrate
users to 4G because it’s more efficient [6].
The urgent demand for wideband LTE coverage
represents a serious challenge facing antenna
vendors who found themselves in trouble, stuck with
the current passive antenna technology trying to
adapt it to serve the wideband demand.
Unfortunately, the current technologies were not
resilient enough to achieve that purpose. So antenna
vendors gave up on it, having a definitive belief that
passive antennas have reached its limits [7].
Therefore, they adopted the active tunable antenna
approach to fulfill the market need for world LTE
devices, trading the passive antenna simplicity with
active antenna complexity. But we can say with
confidence that the passive antenna technology have
not come to an end yet. Passive antennas have
various advantages over the active tunable antennas.
First of all, the passive antenna doesn’t have to be
supported with RF controlling circuit to do the job as
the active one, so it will save large space required
inside the handset to fit both the antenna and the RF
circuit.
The problems of the RF circuit will not end here, as
the additional circuit components connected to the
antenna surely will suffer from impedance mismatch
that will be translated into a severe decrease in the
efficiency of the antenna.
In addition, Active antenna is power consuming, as
the battery life is significantly decreased. Finally,
active antenna seems to have band limitations too, as
the maximum number of bands that commercial LTE
antennas can support is 13 bands out of 35 potential
LTE bands.
On the other hand, Current handset antenna
technology still tide with extended ground plane’s
dilemma, as the antenna is not just the module that
fit under the ear phone but also includes the large
PCB ground plane that must have a minimum size
for the antenna to have an acceptable performance,
adding an extra volume counted on the total size of
the antenna.
Wide band passive antenna
AMANT Antennas is providing the market with a
novel antenna technology to solve the problem of
urgent need for universal LTE devices. The new
technology can cover all the possible LTE spectrum
bands using only two antennas with bandwidths of
73% and 75.8% respectively without using any
matching or tuning circuits. The first antenna is
covering the low band LTE spectrum starting from
698 MHz up to 1.51 GHz which includes LTE band
numbers 5, 8, 11, 12, 13, 14, 17, 18, 19, 20, 21. The
second one is covering the high band portion of the
LTE spectrum starting from 1.71 GHz to 3.8 GHz
corresponding to LTE band numbers 1, 2, 3, 4, 7, 9,
10, 22, 23, 25, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42,
43. This means a total number of 32 LTE bands can
be covered beside the 2G and 3G frequency bands as
700MHz WiMax, CDMA/TDMA/GSM800 (824–
894MHz), low L band GPS (1.2GHz), L-band DVBH (1452–1492MHz), GPS (1575MHz), GSM1800
(1710–1880MHz), PCS1900 (1859–1990MHz),
UMTS
(1900–2170MHz),
Bluetooth/WiFi
(2.4GHz), WiMax (2.3–2.5GHz), and IMT-2000
WiMax (2.5–2.69GHz).
The new antenna technology can be implemented in
smart phone handsets, tablets, laptops and
notebooks. The geometry of the antenna is shown in
Fig.1, which can be scaled and optimized for any
application or any frequency band. Multiple antenna
configurations is provided according to the available
space inside the device with different size choices of
0.1x0.1x15.6 cm, 0.2x0.2x15.6 cm or 0.4x0.4x15.6
cm for the low band antenna and 0.1x0.1x5.55 cm,
0.2x0.2x5.55 cm or 0.4x0.4x5.55 cm for the high
band antenna.
L1
D1
D2 D3 D4
D7
D8
W1
D5
acceptable. Fig. 2 shows the calculated and
measured return loss of the low band antenna. The
return loss is less than -5 dB almost all over the
frequency band from 698 MHz to 1.51 GHz which is
73 % band width.
W2
D6
L2
Short Arm
T
Shorting Strip
Long Arm
Slots
Fig. 2 Calculated & measured return loss of the low
band antenna
Fig. 1 Geometry of the new wideband antenna
The low band antenna design is flexible enough to
be bended and wrapped in the void around the
mobile chassis to overcome the antenna length
problem and make it fit inside the device so it is
completely self-contained and does not need an
additional ground plane or any other components.
Thus, the new antenna can be mounted anywhere
inside or outside any handset because the antenna
does not use a part of the handset as an extended
ground plane as usually happens with internal
antennas.
The total antenna efficiency is shown in Fig.3. The
average efficiency is better than 70% over most of
the low band. Fig.4 demonstrates the peak gain of
the low band antenna which is higher than 1 dB
almost over the whole band. Fig.5 shows the total
radiation pattern at a sample frequency 748 MHz.
Results:
Different prototypes of the new LTE antennas have
been designed, manufactured and tested. The results
of a selected sample antenna configuration will be
presented. The low band antenna performance
having total volume of: 0.4x0.4x15.6 cm=2.496 cm3
is numerically calculated by a software packages that
uses the moment method. It is also measured at
IMST antenna labs in Germany. It should be noted
that the proposed volume is the total volume of the
antenna because it does not require an additional
ground plane or matching circuits. The agreement
between numerical and experimental results was
Fig.3 Efficiency of the low band antenna
Fig.4 Gain of the low band antenna
Fig.6 Calculated & measured return loss of the high
band antenna
Fig.7 shows that the efficiency of this novel antenna
is above 80% over most of the high band and
exceeds 95% at some frequency points. The biggest
portion of the band meets a peak gain above 1 dB as
demonstrated in Fig.8. The total radiation pattern at
sample frequency 2.755 GHz is shown in Fig.9.
Fig.5 Radiation pattern of the low band antenna at
748 MHz
To cover the high band portion of the LTE spectrum,
a second antenna has been designed and
manufactured by scaling and optimizing the
geometry shown in Fig. 1, having total volume of
0.4x0.4x5.55 cm=0.888 cm3 without any additional
ground planes or tuning circuits. The antenna is
tested all over the high frequency band 1.71-3.8
GHz. As shown in Fig.6, most of the calculated and
measured return loss of the high band antenna lay
under -5 dB resulting in 75.8% antenna bandwidth.
Fig.7 Efficiency of the high band antenna
Multiples of low and high band antennas can be used
for MIMO diversity in laptops, tablets and smart
phones. Each of these different situations has been
studied and will be demonstrated next.
the primary & diversity antennas is measured with
laptop and in free space with holding the same
position and space between them. The measured
isolation on laptop gets improved over most of the
band as demonstrated in Fig. 12.
Fig.8 Gain of the high band antenna
Fig. 10 Correlation coefficient between primary and
diversity low band MIMO antennas perpendicular to
each other for laptop and tablets
Fig.9 Radiation pattern of the high band antenna at
2.755 GHz
Laptops and tablets:
The space available inside laptops and tablets is
quite large, so for 2x2 MIMO diversity, one primary
antenna & one diversity antennas can be placed 10
cm apart perpendicular to each other. As a result of
this position of primary & diversity antennas relative
to each other, even though they are broadcasting
over the same frequency band in the same time, the
correlation coefficient and isolation between the two
antennas will be as good as expected. Shown in
Fig.10, the maximum correlation coefficient value is
less than 0.025. Also the calculated isolation is less
than -20 dB and the measured isolation shows better
isolation values much less than -25 dB as
demonstrated in Fig 11. Also the isolation between
Fig. 11 Measured & calculated isolation (S21)
between primary and diversity low band MIMO
antennas perpendicular for laptop and tablets
Fig.12 Measured isolation (S21) between primary
and diversity low band MIMO antennas
perpendicular on laptop and without laptop
The primary & diversity antennas are totally
uncorrelated as previously shown and this can be
further noticed in Fig.13 & Fig.14 as the total
radiation patterns of the primary and diversity
antennas are uncorrelated both at phi=0 & phi=90 as
shown at a sample frequency 901 MHz .
Fig.13 uncorrelated patterns of primary and diversity
antennas at phi=0 at 901 MHz
Fig.14 uncorrelated patterns of primary and diversity
antennas at phi=90 at 901 MHz
The previous experiments are repeated for 2x2
MIMO high band antennas perpendicular to each
other and 10 cm apart for laptops and tablets.
In terms of wavelength, the distance between the
primary and diversity antennas is larger in the high
band which is reflected in a positive way on
correlation coefficient values which are much less
than 0.001 as shown in Fig. 15. Also lower Isolation
than -30 dB in free space and on laptop is shown in
Fig. 16 & Fig. 17.
Fig. 15 Correlation coefficient between primary and
diversity high band MIMO antennas perpendicular
to each other for laptop and tablets
We’ve investigated the worst case scenarios for the
presence of low & high band antennas together in
laptops and tablets and found that the isolation in
different relative positions is acceptable.
Fig. 16 Measured & calculated isolation (S21)
between primary and diversity high band MIMO
antennas perpendicular for laptop and tablets
Fig.18 uncorrelated patterns of primary and diversity
antennas at phi=0 at 2.755 GHz
Fig.17 Measured isolation (S21) between primary
and diversity low band MIMO antennas
perpendicular on laptop and without laptop
Also, the uncorrelated total radiation patterns
demonstrated in Fig. 18 & Fig. 19 is a further
evidence of the minimal correlation between primary
and secondary high band MIMO antennas on laptops
and tablets.
Low band & high band antennas isolation
The ultra wide spectrum of LTE requires the
presence of both of the low band & high band in the
device in the same time to cover the whole spectrum.
This condition will raise concerns about isolation
between high & low bands.
Fig.19 uncorrelated patterns of primary and diversity
antennas at phi=0 at 2.755 GHz
The first case scenario investigated was the low band
antenna parallel to the high band antenna at 10 cm
distance between them. As shown in Fig. 20 & Fig.
21, the isolation all over both low and high bands is
lower than -30 dB.
Fig. 20 Measured & calculated isolation (S21) in
low frequency band between low band and high
band antennas while parallel to each other
Fig. 22 Measured isolation (S21) in low frequency
band between low band and high band while parallel
to each other on laptop
Fig. 21 Measured & calculated isolation (S21) in
high frequency band between low band and high
band antennas while parallel to each other
Fig. 23 Measured isolation (S21) in low frequency
band between low band and high band while parallel
to each other on laptop.
When the isolation between low & high band
antennas has been investigated experimentally for
laptop case study, it also demonstrated very good
isolation values lower than -30 dB for free space & 40 dB for laptop over most of the low and high
bands as shown in Fig. 22 & Fig. 23 respectively.
The second case scenario that has been studied was
the low band and high band antennas perpendicular
to each other and 10 cm apart. The results
demonstrated in Fig. 24 & Fig. 25 shows lower than
-40 dB isolation over almost the whole frequency
band. The experimental comparisons between
isolation in free space & on laptop are also shown in
Fig. 26 & Fig. 27.
Fig. 24 Measured & calculated isolation (S21) in
low frequency band between low band and high
band antennas while perpendicular to each other
Fig. 25 Measured & calculated isolation (S21) in
high frequency band between low band and high
band antennas while perpendicular to each other.
Smart phones:
The low band antenna can be customized for smart
phones. It can be bent as an “L” shape to fit in the
void around the chassis of the handset. This
customization has been studied theoretically and
experimentally for 2x2 MIMO and the results will be
discussed below.
Fig. 26 Measured isolation (S21) in low frequency
band between low band and high band while
perpendicular to each other on laptop
Fig. 27 Measured isolation (S21) in high frequency
band between low band and high band while
perpendicular to each other on laptop.
As shown in Fig. 28, low band antenna lapelled no.
1 is the primary antenna and the other low band
antenna lapelled no.2 is the diversity antenna. The
primary and diversity antennas are wrapped in “L”
shape configuration to overcome the extra length
problem of the low band antenna. The measured &
calculated return loss of both antennas is lower than
-5 dB over most of the low band from 698 MHz to
1.51 GHz for both primary and diversity antennas as
demonstrated in Fig.29 & Fig.30 respectively.
The primary & diversity antenna’s efficiencies are
higher than 60% & 50% respectively over most of
the low band as demonstrate in Fig. 31. Also a peak
gain higher than 1 dB over most of the band for both
the primary & diversity antennas shown in Fig. 32.
2
1
Fig. 28 The schematic diagram of MIMO low band
antennas on mobile
Fig. 31 Efficiency of primary & diversity low band
antennas
Fig.29 Calculated & measured return loss of the
primary low band antenna
Fig. 32 Gain of primary & diversity low band
antennas
The isolation between the primary and diversity
antennas has been investigated and a lower than -10
dB measured isolation in free space can be accepted
as shown in Fig. 33. Demonstrated in Fig. 34, the
measured isolation on mobile was much promising
over most of the band, as it has average of -15 dB.
Fig.30 Calculated & measured return loss of the
diversity low band antenna
As proven in Fig. 36 & 37, the low correlation
values over the low frequency band is an indication
of uncorrelated radiation patterns of primary and
diversity antennas relative to each other at both
phi=0 and phi=90 at sample frequency 901 MHz.
Fig. 33 Measured & calculated isolation (S21)
between primary and diversity low band antennas
Fig. 36 uncorrelated patterns of primary and
diversity antennas at phi=0 at 901 MHz
Fig. 34 Measured isolation (S21) between primary
and diversity low band antennas with & without
presence of mobile
The correlation coefficient between primary and
diversity antennas was lower than 0.55 as shown in
Fig. 35.
Fig. 37 uncorrelated patterns of primary and
diversity antennas at phi=90 at 901 MHz
2x2 MIMO high band antennas have been also tested
theoretically and experimentally and their relative
position to each other has been optimized for the
implementation in smart phones. The best results
were due to the position shown in Fig. 38, where
antenna lapelled no.1 is the primary and antenna
lapelled no.2 is the diversity.
Fig. 35 Correlation coefficient between primary and
diversity low band antennas
1
2
Fig. 38 The schematic diagram of 2x2 MIMO high
band antennas on mobile
Fig. 40 Measured isolation (S21) between primary
and diversity high band antennas in free space & on
mobile
Measured isolation (S21) of as low as -30 dB
between primary & diversity MIMO antennas shown
in Fig. 39 & Fig. 40, is an expected result of the
perpendicular position of primary antenna relative to
diversity antenna which is considered the best
isolation technique in such a small available space
inside handsets.
The perpendicular relative position also has its
positive effect on the correlation coefficient which is
generally lower than 0.1 and most of the high
frequency band is lower than 0.01 as shown in Fig.
41.
Fig. 39 Measured & calculated isolation (S21)
between primary and diversity high band antennas
Fig. 41 Correlation coefficient between primary and
diversity high band MIMO antennas perpendicular
to each other for smart phones
The resulted uncorrelated patterns of the primary &
diversity antenna are demonstrated at phi=0 &
phi=90 at sample frequency 2.755 GHz in Fig. 42 &
43 respectively.
3
4
2
Fig. 42 uncorrelated patterns of primary and
diversity antennas at phi=0 at 2.755 GHz
1
Fig. 44 The schematic diagram of MIMO wide band
antenna solution for LTE smart phones
The biggest concern in this case is the isolation
values between the low and high band antennas. The
isolation is tested for this case and results were
mostly lower -20 dB for low band and high band
frequency spectrum as shown in Fig. 45 & Fig 46
respectively.
Fig. 43 uncorrelated patterns of primary and
diversity antennas at phi=90 at 2.755 GHz
The urgent demand for universal LTE smart phones
requires an antenna solution that is able to cover
most of LTE bands for global roaming. By
combining our two wide band antennas together in
one device, it will fulfill that need. A schematic
diagram for our MIMO wide band antenna solution
is demonstrated in Fig. 44
As shown in Fig. 44 the high band antennas no. 3 &
4 are located in a higher plane above the low band
antennas by 1 mm.
Fig. 45 isolation between each low band and high
band antenna in the low band frequency spectrum
purpose. The dual feeds are lapelled 1 & 2 in Fig.
48.
2
Fig. 46 isolation between each low band and high
band antenna in the high band frequency spectrum
Dual feed antenna
In some cases the available space inside handsets is
very limited and the number of MIMO antennas will
represent a problem. We have developed another
wide band LTE antenna solution for handsets that
will save large volume inside the device by dual feed
technique in one antenna, so the multiband LTE can
be covered only by two antennas as shown in Fig.47.
1
Fig. 48 The schematic diagram of MIMO low band
antenna solution for LTE smart phones
The low band dual feed antenna has been tested for
obtaining return loss due to the first feed S11 , return
loss due to second feed S22 and the isolation
between them S21 as shown in Fig. 49.
Fig. 49 s parameters for dual feed low band antenna
Fig. 47 The schematic diagram for MIMO dual feed
LTE antennas
The first antenna in this solution is the low band
antenna; it is a dual feed for 2x2 MIMO diversity
The resulted correlation coefficient between the two
feeds is lower than 0.5 for the low band antenna as
shown in Fig. 50.
Fig. 50 Correlation coefficient between feed 1 &
feed 2 for low band antenna
The second antenna in the wide band LTE antenna
solution for the handsets is the high band antenna
which is also having dual feeds for 2x2 MIMO
diversity. The 2 feeds lapelled 1 & 2 are shown in
Fig. 51.
1
Fig. 52 s parameters for dual feed high band antenna
2
Fig. 53 Correlation coefficient between feed 1 &
feed 2 for high band antenna
Improving LTE antenna performance
Fig. 51 The schematic diagram of MIMO high band
antenna solution for LTE smart phones
The high band dual feed antenna has been tested for
obtaining return loss due to the first feed S11 , return
loss due to second feed S22 and the isolation
between them S21 as shown in Fig. 52.
The resulted correlation coefficient between the two
feeds is lower than 0.6 for the low band antenna as
shown in Fig. 53.
As shown above, our wide band antenna can cover
most of the LTE frequency spectrum. However, the
small space available for the antenna inside the
devices makes it a compromise process: To fit the
antenna inside such small space makes us accept
lower but acceptable efficiencies. As the available
space is larger it would be desirable & easy to
increase the efficiency by increasing the width and
thickness of the antenna as much as possible. A new
antenna has been developed for this purpose having
a total volume of 1.3x0.4 x14.5=7.54 cm3. Fig. 54
shows the return loss of the increased size antenna,
which is lower than -8 dB over most of the band
having minimum value of -5dB. The total efficiency
shown in Fig. 54 demonstrates minimum efficiency
of 70% and reaches its maximum at 96%. The
average gain of the newly developed antenna is
higher than 1dB as shown in Fig. 56. The radiation
patterns at phi=0 & phi=90 at 901 MHz are also
demonstrated in Fig. 57.
Fig. 56 Improved gain of the increased size antenna
Fig. 57 Radiation pattern of the increased size
antenna at 901 MHz
References:
[1] “LTE: The Future of Mobile Broadband
Technology”, Verizon wireless.
Fig. 54 Improved Return loss (S11) of the increased
size antenna
Fig. 55 Improved efficiency of the increased size
antenna
[2] P. Vainikainen, J. Holopainen, C. Icheln, O.
Kivekas, M. Kyro, M. Mustonen, S. Ranvier, R.
Valkonen, and J. Villanen, “More than 20 antenna
elements in future mobile phones, threat or
opportunity?”, Antennas and Propagation, 2009,
EuCAP 2009. 3rd European Conference on 23-27
March 2009, pp. 2940-2943.
[3] Byoung-Nam Kim, Seong-Ook Park, Jung-Keun
Oh, and Gwan-Young Koo, “Wideband Built-In
Antenna with New Crossed C-Shaped Coupling
Feed for Future Mobile Phone Application”, IEEE
antennas and wireless propagation letters, vol. 9, pp.
572-575 , 2010.
[4]http://www.wirelessintelligence.com/analysis/201
1/12/global-lte-network-forecasts-and-assumptionsone-year-on/
[5] “Next Generation Mobile Networks Initial
Terminal Device Definition”, NGMN Alliance,
November, 2010.
[6]http://www.globaltelecomsbusiness.com/Article
/2948514/Sectors/25196/38-fragmented-
frequencies-confuse-scale-benefits-of-LTEterminals.html
[7] http://mobiledevdesign.com/tutorials/4g-devicesdemand-active-antenna-solutions-0216/?cid=ed