chapter 1 introduction - wordpress.com · chapter 1 introduction ... analyzed in detail for the...
TRANSCRIPT
1
CHAPTER 1
INTRODUCTION
Now-a-days, wireless communication system plays a vital role in human’s
life where a person can exchange information in the world with fast forward
capabilities and high speed .Such a need for fast forward and high speed exchanges
can be achieved by a assuring technology like multiple input multiple output
(MIMO).In September 2009, IEEE Standard Association has endorsed the IEEE
802.11n standard [2]. Multiple Input Multiple Output is a wireless technology that
handles various transmitters and receivers to transfer enormous amount of data at
the same time. In recent days it is evident that multiple antennas are having a better
quality of demand and are most of expected to be tightly packed within devices
that do not cover a large area. It creates a great challenge to incorporate these
multiple antennas into smaller devices like USB due to the limited availability of
area. Another difficulty that arises is that the effect of coupling that are a serious
issues in multiple antennas.
In recent days, there is a huge need for high speed USB dongles that enables
us access to broad band internet services. A proper implementation of a multiple
antenna for UWB USB application will give rise to an excess need of isolation
between the radiating elements over smaller region of space. It is evident from the
recent studies that to improvise the isolation among antenna elements so that it will
perform independently. In order to increase the isolation between the antenna
elements, method of neutralization line is used, then the size of PCB is large which
covers only WLAN band (2.45 GHz)[4]. To establish the functions like all stop
filter and elevation of port isolation, we use a couple of open ended subs. The
structure proposed by the authors uses a 3- Dimensional structure which resonates
2
over WLAN, WiMAX, HiperLAN. To improve isolation between ports [5,6] a 3
dimensional structure is proposed with a protruded ground plane. Here the area of
the antenna is quite big which tends to cover the most regions in the PCB of the
Dongle. The facilities of broadband mobile internet services are given access by
the inclusion of WiMAX in the later stages at higher data transfer speeds. The
combination of WLAN and WiMAX range of frequencies is highly needed for
USB Dongle applications.
The reason why we go for printed antennas is that it will help us understand
the scenario behind the evolution of antennas that are cost effective, less complex
fabrication techniques and simple design.
This explains the necessity for an antenna with a simple geometry and better
isolation techniques.
Here we have designed a small printed UWB monopole antenna that
resonates WLAN, WiMAX, HiperLAN for USB dongle application. The basic
function of this antenna is that it can be plugged to the USB port of the PC or a
compatible device so that it can provide the services offered by the proposed
frequency ranges.
The most commonly arising problem in these antennas is the mutual
coupling that deteriorates the effectiveness of the proposed antenna. This problem
is avoided by using neutralization line and Defected Ground Structure (a modified
Ground). The high isolation techniques used in this antenna helps us evade the
isolation that persisted in these antennas. The simulation process for this antenna is
carried out with the help of Finite Element Method (FEM) which corresponds to
the Ansoft’s High Frequency Structure Simulator (HFSS). Here we compare the
proposed antenna with previously done works in terms of the characteristics such
3
as diversity techniques, isolation methods, operating bands and radiation
characteristics.
Multiple-input multiple-output, or MIMO, is a radio communications
technology or RF technology that is being mentioned and used in many new
technologies these days. Wi-Fi, LTE; Long Term Evolution, and many other radio,
wireless and RF technologies are using the new MIMO wireless technology to
provide increased link capacity and spectral efficiency combined with improved
link reliability using what were previously seen as interference paths.
A channel may be affected by fading and this will impact the signal to noise
ratio. In turn this will impact the error rate, assuming digital data is being
transmitted. The principle of diversity is to provide the receiver with multiple
versions of the same signal. If these can be made to be affected in different ways
by the signal path, the probability that they will all be affected at the same time is
considerably reduced. Accordingly, diversity helps to stabilize a link and improves
performance, reducing error rate.
Several different diversity modes are available and provide a number of
advantages:
Time diversity: Using time diversity, a message may be transmitted at
different times, e.g. using different timeslots and channel coding.
Frequency diversity: This form of diversity uses different frequencies. It
may be in the form of using different channels, or technologies such as
spread spectrum / OFDM.
Space diversity: Space diversity used in the broadest sense of the definition
is used as the basis for MIMO. It uses antennas located in different positions
4
to take advantage of the different radio paths that exist in a typical terrestrial
environment.
MIMO is effectively a radio antenna technology as it uses multiple antennas
at the transmitter and receiver to enable a variety of signal paths to carry the data,
choosing separate paths for each antenna to enable multiple signal paths to be used.
General Outline of MIMO system
One of the core ideas behind MIMO wireless systems space-time signal
processing in which time (the natural dimension of digital communication data) is
complemented with the spatial dimension inherent in the use of multiple spatially
distributed antennas, i.e. the use of multiple antennas located at different points.
Accordingly MIMO wireless systems can be viewed as a logical extension to the
smart antennas that have been used for many years to improve wireless.
It is found between a transmitter and a receiver the signal can take many
paths. Additionally by moving the antennas even a small distance the paths used
will change. The variety of paths available occurs as a result of the number of
objects that appear to the side or even in the direct path between the transmitter and
receiver. Previously these multiple paths only served to introduce interference. By
using MIMO, these additional paths can be used to advantage. They can be used to
provide additional robustness to the radio link by improving the signal to noise
ratio, or by increasing the link data capacity.
5
The two main formats for MIMO are given below:
Spatial diversity: Spatial diversity used in this narrower sense often refers
to transmit and receive diversity. These two methodologies are used to
provide improvements in the signal to noise ratio and they are characterized
by improving the reliability of the system with respect to the various forms
of fading.
Spatial multiplexing: This form of MIMO is used to provide additional
data capacity by utilizing the different paths to carry additional traffic, i.e.
increasing the data throughput capability.
As a result of the use multiple antennas, MIMO wireless technology is able
to considerably increase the capacity of a given channel while still obeying
Shannon's law. By increasing the number of receive and transmit antennas it is
possible to linearly increase the throughput of the channel with every pair of
antennas added to the system. This makes MIMO wireless technology one of the
most important wireless techniques to be employed in recent years. As spectral
bandwidth is becoming an ever more valuable commodity for radio
communications systems, techniques are needed to use the available bandwidth
more effectively. MIMO wireless technology is one of these techniques.
6
CHAPTER 2
LITERATURE REVIEW
[1]. Printed Monopole Diversity Antenna for Dongle Application.
This paper introduces a compact monopole diversity antenna for USB
dongle applications which support broadband mobile internet services. The good
isolation performance (below -14 dB at WLAN, HiperLAN and WiMAX
frequency bands) is achieved by applying the combination of DGS and
neutralization line techniques. Further, mechanism of neutralization line is
demonstrated with help of circuit model and surface current distribution. The
measured radiation patterns show that the proposed antenna having the capability
to mitigate the fading effect in multipath propagation. Moreover, the antenna
elements have excellent ECC and MEG values resulting that the proposed antenna
shows superior diversity performances. The proposed antenna is covered the desire
operating bands and good isolation characteristics is achieved on the actual
application platform (with USB dongle and Laptop structure), which insist that the
antenna can be realized on actual platform.
[2]. Printed MIMO-Antenna System Using Neutralization-Line Technique for
Wireless USB-Dongle Applications.
A printed, two-monopole-antenna system decoupled by using the
neutralization- line technique has been demonstrated to attain good antenna port
isolation, and the constructed prototype has been successfully constructed and
tested. Each antenna is of the same size and occupies a clearance layout area of 8
mm 14.5 mm on the two opposite corners of the system PCB with a small ground
portion between the antennas. The neutralization line in this design does not
occupy much board space of the system ground plane and only takes 1.5 mm long
7
inwards from the PCB edge in the small ground portion. In this case, the antenna
feeding network and the I-PEX connectors can be all placed on that small ground
portion for practical applications. The results showed that the obtained antenna
port isolation is less than about 19 dB and is better than that of the reference case
with no neutralization line by about 9 dB. The envelope correlation and the TARC
were also studied and derived from the parameters. The radiation patterns of the
two monopoles cover the complementary space regions in general, and the antenna
yields peak gain of about 2.1 dBi with radiation efficiency exceeding about 70%.
The impedance of the isolation, the surface currents, and the near fields were
analyzed in detail for the effects of the neutralization line used.
[3]. Closely-Packed UWB MIMO/Diversity Antenna with Different Patterns
and Polarizations for USB Dongle Applications.
In this paper, a closely-packed UWB MIMO/diversity antenna with a size of
25 mm 40 mm is proposed for USB dongle applications. Through different
radiation patterns and polarizations of the two antenna elements, wideband
isolation has been achieved. The proposed antenna can cover the lower UWB band
of 3.1–5.12 GHz with an isolation of higher than 26 dB. The underlying
mechanisms that contribute to the good impedance bandwidth and high isolation
are carefully explained. The radiation patterns, gains and efficiencies of two
antenna elements have also been measured. The measurement results confirm that
the proposed UWB MIMO/diversity antenna is suitable for MIMO USB dongle
applications.
8
[4]. Compact Dual-Band WLAN Diversity Antennas on USB Dongle Platform
The proposed compact, dual-band two-antenna system was studied
rigorously with various evaluation measures to validate its superior performance.
Sizes of the overall two-antenna system, which includes the two chips, the feed
strips, the tuning stubs, and clearance regions, are only 13 mm 6.5 mm 2.4 mm.
Considering the small form factor, its performances exceed or are on par with
current dual-band WLAN antenna designs in terms of impedance matching,
operation bandwidth, and radiation efficiency. The port isolation is exceptional
since the separation distance is 1 mm only. Antenna diversity measures such as
ECC and EDG were assessed. Results suggest the proposed system shall provide a
decent figure of merit for diversity uses.
Mechanisms for achieving dual-band operation with such a small antenna
volume are analyzed. The 2.4 GHz band isolation is realized principally via pattern
diversity. The HiperLAN band isolation is achieved by a pair of open-ended stubs
connected in parallel with the feed strips. The stub pair geometry is similar to a
micro strip line all-stop filter. It hence success-fully suppresses antenna coupling in
the band where the quarter wavelength line approximation is valid. This novel
practice pro-vides an example that circuit component can be move onto or next to
the antenna structure to accomplish port isolation among closely spaced feeds.
[5]. A Wideband Printed Dual-Antenna with Three Neutralization Lines for
Mobile Terminals
In this paper, a printed dual-antenna decoupled by three NLs operating at the
GSM1800, GSM1900, UMTS, LTE2300, LTE2500, and 2.4GHz WLAN bands for
mobile terminals has been investigated. The dual-antenna, consisting of two
9
symmetric antenna elements and three NLs is printed on a PCB. The three NLs
reduce the mutual coupling between the two antenna elements. The working
mechanism of the three NLs is analyzed. A prototype shows that the measured -
10dB impedance bandwidth is 1.3GHz (1.62-2.92 GHz). Between 1.66 and
2.84GHz, the measured radiation patterns can cover complementary spatial
regions. The calculated envelope correlation coefficient and the MEGs satisfy the
criteria of low correlation and comparable average receiving power, respectively.
The diversity gains of nearly 10dB are achieved.
[6]. Isolation Enhancement Between Two Closely Packed Antennas
In this paper, a coupling element to enhance isolation for closely packed
antennas operating at the same frequency is proposed. We artificially create an
additional coupling path by utilizing a coupling element to neutralize the coupling
between the antenna elements. A simplified dipole model is introduced to
demonstrate the proposed concept with the coupling element for improving
isolation. A practical, compact and low-cost USB WLAN MIMO dongle with 2
antennas for use in 2.4GHz WLAN 802.11n, is designed and demonstrated. In the
design, the antenna elements with coupling element are located on compact PCB,
with dimensions 20 × 40 × 1.6 mm and etched on low cost FR4 board. The MIMO
USB dongle antenna was simulated and prototyped for verification. It operate in
802.11b WLAN band for MIMO application with maximum 30 dB isolation, 2dBi
peak gain and 60% efficiency with their spacing (center to center) less than 0.095
(11.6 mm) or edge to edge separations just 3.6mm (0.0294). Various parameters
are evaluated to see how they can be used to tune the frequency band of the
maximum isolation, peak isolation and the bandwidth of the transmission
reduction.
10
[7]. Low mutual coupling between MIMO antennas by using two folded
shorting strips
In this paper, a compact dual band MIMO antenna with low mutual coupling
operating over WLAN bands (2.4–2.485 GHz and 5.15– 5.85 GHz) is proposed.
The measured 6-dB return loss bandwidths are 510 MHz and 1700 MHz over
lower and higher resonating frequencies respectively. Excellent isolation is
achieved between two antenna elements by folded shorting strip. The antenna total
efficiencies are improved 10% averagely over the operating frequency bands, and
also the improved isolation values are less than −28 dB at WLAN 11.b/g band and
better than −26 dB (−30 dB in most of the band) across WLAN 11.a band. The
radiation patterns of two antennas are providing good pattern diversity
characteristics and also we obtained excellent ECC (lower than 0.01), well
diversity gains and the satisfactory MEG ratios over the frequency of interested
bands. These indicate that our proposed antenna has a good MIMO/diversity
performance and suitable for mobile handset applications.
11
CHAPTER 3
ANTENNA DESIGN AND CONFIGURATION
For many years, the ultra-wideband (UWB) communication systems have
gained much attention because of their low spectral power density, large channel
capacity, and high data rates without influence on other systems. It is well known
that a diversity antenna offers attractive applications in wireless communications
since it gives out much higher channel capacities compared with using a single
antenna. Federal Communications Commission (FCC) has allocated a licence free
band of 3.1–10.6GHz for UWB communication in 2002.
Figure 3.4 shows the configuration of the proposed MIMO antenna. It
consists of two identical monopoles which are printed symmetrically with respect
to the symmetrical line on FR4 substrate. The detail dimensions of single antenna
element and neutralization line are shown in Fig.3.1. The single antenna element of
proposed MIMO antenna system consists of two arms namely, Arm 1 and Arm 2.
To obtain desired resonances as well as better isolation, length and width of the
arms along with the connection point of the neutralization line with main radiating
elements are optimized. The optimized shape parameters for the proposed antenna
have been attained by the stringent parametric study with the aid of
electromagnetic simulator, Ansoft’s HFSS.
The design of Arm 1 and Arm 2 are based on the concept of monopole [11].
The total physical length of the Arm 1 is around quarter-wavelength at 2.18 GHz
which is lower edge cut-off frequency as shown in reflection coefficient plot. The
independent operation of Arm 1 provides the wide bandwidth from 2.18 to 4.26
GHz but unable to cover the HiperLAN frequency band. However, the physical
12
length of Arm 2 is quarter wavelength at 2 GHz which is lower edge cut-off
frequency as shown Fig. 3.2.1. The independent operation of Arm 2 provides dual
band behaviour which resonates at 2.2 and 3.4 GHz. But this configuration is also
ineffective to provide the WLAN and HiperLAN frequency bands.
The independent operation of each arm is unavailing to find desired goal.
Therefore, to achieve WLAN, WiMAX, and HiperLAN frequency bands
simultaneously, both the arms are combined together along with the neutralization
line. The frequency bands of antenna as well as isolation are found to be
effectively improved by linking the two highly-coupled monopoles and results are
shown in Fig. 3.3.1. Although, low impedance area(with minimum voltage but
maximum currents) of the antenna is favorable location to connect the
neutralization line [12]. From Fig. 3.5.1, it is elucidated that the proposed antenna
provides the WLAN (2.4–2.48 GHz), WiMAX (3.4–3.8 GHz), and HiperLAN
(4.7–5.83 GHz) bands with respect to the -10 dB reflection coefficient and
isolation between ports is better than -14 dB over all the operating bands.
It is noticed that the isolation at lower frequency side is very poor around -5
dB in absence of isolation techniques. This poor behaviour of isolation suggests
that the isolation can be effectively improved by incorporating the neutralization
line along with DGS. After rigorous optimization, desired frequency bands and
excellent isolation characteristic between antenna elements (better than -14 dB
over all the operating bands) are achieved.
13
Fig 3.1.Details of single elements: a single antenna element; b
neutralization line
Fig.3.2.Description of Proposed UWB MIMO antenna for dongle applications
14
Fig 3.3.Back view
Table 3.1.Dimension of the antenna
Parameters Size(mm) Parameters Size(mm) Parameter Size(mm)
a1 3 a7 5.5 c1 8
b1 1 b7 3 d1 0.75
a2 0.5 a8 1.75 c2 1.5
b2 15.25 b8 0.5 d2 4.75
a3 1 a9 3 c3 2.75
b3 15.25 b9 0.75 d3 5
a4 1.25 a10 0.5 c4 1
b4 4 b10 5 d4 7.2
a5 3.25 a11 1.25 c5 3.9
b5 1.5 b11 9.25 d5 1
a6 3.5 L 60 c6 10.75
b6 1.25 W 25 d6 0.3
15
3.1 Design of ARM1
The design of Arm1 and Arm2 is based on the concept of monopole. The
total physical length of the Arm1 is around quarter-wavelength at 2.18GHz which
is lower edge cut-off frequency. The independent operation of Arm 1 provides the
wide bandwidth from 2.18 to 4.26 GHz but unable to cover the HiperLAN
frequency band. The effect of reflection coefficient and structure of arm1 is shown
below.
Fig 3.1.1 a.Arm1 design b. Effect of reflection coefficient.
16
3.2 Design of ARM2
The physical length of Arm 2 is quarter wavelength at 2GHz which is lower
edge cut-off frequency. The independent operation of Arm2 provides dual band
behaviour which resonates at 2.2 and 3.4 GHz .The effect of reflection coefficient
and structure of arm 2 is shown below.
Fig 3.2.1 a. Arm2 design b. Effect of reflection coefficient.
17
3.3 Combining Arm 1 and Arm 2 without Neutralization line
By combining the arm1 and arm 2 without neutralization line provides the
bandwidth of HiperLAN but unable to cover the WiMAX frequency band. In order
to cover the WiMAX band we can use a neutralization line technique and defected
ground structure (DGS). The reflection coefficient and structure of combining
arm1 and arm 2 are shown below.
Fig 3.3.1.a. Combining Arm 1 and Arm 2design b. Effect of reflection coefficient.
18
3.4 Combining Arm 1 and Arm 2 with Neutralization line without
modification of DGS
By combining the arm1 and arm 2 with the neutralization line we can
achieve the WiMAX frequency band and also effectively reduce the mutual
coupling between the two antennas.
Fig 3.4.1.a. Combining Arm 1 and Arm 2 with Neutralization line b. effect of
reflection coefficient.
3.5 Modeling of the Neutralization Line
Further, to understand the mechanism of neutralization line a simplified
equivalent model is built. The equivalent model and its equivalent circuit are
shown in Fig. 3.5.1. When port 1 is stimulating by a current ‘I’ then some fraction
19
of current ‘I’ i.e. ‘cI’ is coupled to the Antenna 2. To reduce this coupling, a
neutralization line is proposed which is connected between antenna elements at
points ‘A’ and ‘B’. So, the coupling current ‘nI’ is induced at neutralization line
and remaining currents ‘aI’ is going to Antenna 1. So, a coupling current ‘c* I’ is
coupled to the Antenna 2. To make the mutual coupling is close to zero, the
coupling current ‘c* I’ and some fraction of current ‘I’ i.e. original coupling
current ‘cI’ are designed to a proper value, which is denoted by [1],
cI + c*I=0 (1)
From the equivalent circuit model as shown in Fig. b is observed that at
point ‘A’, Zantenna is input impedance looking towards the antenna elements
whereas Zneutralization is input impedance looking towards neutralization line. From
the circuit model, the coefficient ‘n’ and ‘a’ can be represented as [2]
𝑛 =𝑍𝑎𝑛𝑡𝑒𝑛𝑛𝑎
𝑍𝑎𝑛𝑡𝑒𝑛𝑛𝑎+𝑍𝑛𝑒𝑢𝑡𝑟𝑎𝑙𝑖𝑧𝑎𝑡𝑖𝑜𝑛 (2)
When the coupling current ‘nI’ goes to Antenna 2 through neutralization
line, a combined coupling coefficient ‘c*’ is generated which can be approximately
represented as [3]
𝑎 =𝑍𝑛𝑒𝑢𝑡𝑟𝑎𝑙𝑖𝑧𝑎𝑡𝑖𝑜𝑛
𝑍𝑎𝑛𝑡𝑒𝑛𝑛𝑎+𝑍𝑛𝑒𝑢𝑡𝑟𝑎𝑙𝑖𝑧𝑎𝑡𝑖𝑜𝑛 (3)
20
Fig. 3.5.1 Equivalent model of dual-antenna with neutralization line:
a. equivalent model; b. equivalent circuit
3.6 Combining Arm 1 and Arm 2 with Neutralization line with modification of
DGS
So it is evident that the independent operation of the two Arms doesn’t cover
the exact ranges of frequencies we needed. Hence in order to make the antenna
resonate all the three bands i.e. WLAN, WiMAX, HiperLAN we amalgamate the
two arms with the help of a neutralization line. The figure 3 provides vital
information for us to infer that the antenna resonates WLAN (2.4-2.48GHz),
WiMAX (3.4-3.8GHz), HiperLAN (4.7-5.83GHz) bands with respect to -10dB
reflection coefficient and isolations between ports is better than -14dB over all
frequency bands. The isolation is very poor around -5dB at the lower frequency
side in non-appearance of isolation techniques. This poor isolation would be
effectively increased by integrating the neutralization line along with DGS. After
the precise optimization, expected frequency bands and good isolation
characteristic between antenna elements are obtained.
21
Fig 3.6.1a. Combining Arm 1 and Arm 2 with Neutralization line with
modification of DGS b. Effect of reflection coefficient.
Fig 3.6.2. Effect of transmission coefficient
22
CHAPTER 4
SIMULATION TOOL
4.1 HFSS SOFTWARE
HFSS is antenna simulation software. Besides that it can be used in the
design of an integrated circuit, a high speed interconnect or any other type of
electronic component, HFSS often is used during the design stage, and is an
integral part of the design process.
4.2 THE MATHEMATICAL METHOD USED BY HFSS
HFSS often is used during the design stage, and is an integral part of the
design process. HFSS™ uses a numerical technique called the Finite Element
Method (FEM). This is a procedure here a structure is subdivided into many
smaller subsections called finite elements. The finite elements used by HFSS are
tetrahedral, and the entire collection of tetrahedral is called a mesh. A solution is
found for the fields within the finite elements, and these fields are interrelated so
that Maxwell’s equations are satisfied across inter-element boundaries yielding a
field solution for the entire, original, structure. Once the field solution has been
found, the generalized S-matrix solution is determined.
4.3. Six general steps in HFSS simulation
There are six main steps HFSS simulation.
They are
1. Create model/geometry
2. Assign boundaries
3. Assign excitations
4. Set up the solution
23
5. Solve
6. Post-process the results
Fig 4.1.mathematical method used by HFSS
STEP1: The initial task in creating an HFSS model consists of the creation of the
physical model that a user wishes to analyze. This model creation can be done
within HFSS using the3D modeler. The 3D modeler is fully parametric and will
allow a user to create a structure that is variable with regard to geometric
dimensions and material properties. A parametric structure, therefore, is very
useful when final dimensions are not known or design is to be “tuned.”
Alternatively, a user can import 3D structures from mechanical drawing packages.
Geometry, once imported into HFSS, can be modified within the 3D modeling
environment. This will then create geometry that can be parameterized.
24
Fig 4.2 General steps in HFSS simulation
STEP2: The assignment of “boundaries” generally is done next. Boundaries are
applied to specifically created 2D (sheet) objects or specific surfaces of 3D objects.
Boundaries have a direct impact on the solutions that HFSS provides; therefore,
user is encouraged to closely reviewing the section on Boundaries in this
document.
STEP3: After the boundaries have been assigned, the excitations (or ports)should
be applied. As with boundaries, the excitations have a direct impact on the quality
of the results that HFSS will yield for a given model. Because of this, users are
again encouraged to closely review the section on excitations in this document.
While the proper creation and use of excitations is important to obtaining the most
accurate HFSS results, there are several convenient rules of thumb that a user can
follow. These rules are described in the excitations section.
STEP 4: Once boundaries and excitations have been created, the next step is to
create a solution setup. During this step, a user will select a solution frequency, the
desired convergence criteria, the maximum number of adaptive steps to perform
25
frequency band over which solutions are desired, and what particular solution and
frequency sweep methodology to use.
STEP 5: When the initial four steps have been completed by an HFSS user, the
model is now ready to be analyzed. The time required for an analysis is highly
dependent upon the model geometry, the solution frequency, and available
computer resources. A solution can take from a few seconds. It is often beneficial
to use the remote solve capability of HFSS to send a particular simulation run to
another computer that is local to the user’s site. This will free up the user’s PC so it
can be used to perform other work.
STEP6: Once the solution has finished, a user can post-process the results. Post
processing of results can be as simple as examining the S-parameters of the device
modeled or plotting the fields in and around the structure. Users can also examine
the far fields created by an antenna. In essence, any field quantity or S, Y, Z
parameter can be plotted in the post-processor. Additionally, if a parameterized
model has been analyzed, families of curves can be created.
4.4 Design Flow Chart
1. Parametric Model Generation – creating the geometry, boundaries
and excitations
2. Analysis Setup – defining solution setup and frequency sweeps
3. Results – creating 2D reports and field plots
4. Solve Loop - the solution process is fully automated
26
Fig 4.3. Design flow chart
27
CHAPTER 5
DIVERSITY CHARACTERISTICS
To analysis the diversity performance of designed MIMO antenna, important
parameters such as the envelope correlation coefficient, effective diversity gain and
mean effective gain values are obtained.
5.1 Envelope Correlation Coefficient:
Normally, ECC is used to analyze the diversity capability of MIMO antenna.
This parameter is calculated either by using S-parameters or 3D radiation patterns.
It tells us how independent two antennas radiation pattern are. So if one antenna
was completely horizontally polarized and the other was completely vertical
polarized, the two antennas would have a correlation of zero. Similarly, if one
antenna only radiated energy towards sky, and the other radiated energy towards
ground, these antennas would also have an ECC of 0. Hence, Envelope Correlation
Coefficient takes into account the antennas’ radiation pattern shape, polarization,
and even the relative phase of the fields between the two antennas.
ECC Defined in terms of S-parameters: The most suitable way to conclude
the mutual coupling between antennas through the use of ECC defined in Eq. 1,
which presumed antenna terminal would be matched and uniformly distributed
incoming waves and formula given as ,
𝜌𝑒𝑖𝑗 =|𝑆𝑖𝑖
∗ 𝑆𝑖𝑗+𝑆𝑗𝑖∗ 𝑆𝑗𝑗|
2
(1−(|𝑆𝑖𝑖|2
+|𝑆𝑗𝑖|2
))(1−(|𝑆𝑗𝑗|2
+|𝑆𝑖𝑗|2
))
(4)
Since 𝜌𝑒𝑖𝑗 is completely defined by S-parameters of ith and jth elements in a
multi-antenna system, this parameter can be easily accessed. This equation needs
reflection coefficient of each antenna and transmission coefficient between them.
The mentioned formula is valid for ideal antenna cases but practically the above
28
prediction is failed. Otherwise, the exact ECC calculation we use the far field
method.
ECC Defined in terms of radiation patterns: The ECC can also be defined in
terms of antenna radiation pattern which is given by,
𝜌𝑒 = |𝜌𝑐|2 (5)
Using the radiation patterns, the simplified complex cross-correlation is given by,
𝜌𝑒 =∫ ∫ 𝐴12(𝜃,𝜑)
𝜋
0
2𝜋
0sin 𝜃𝑑𝜃𝑑𝜑
√∫ ∫ 𝐴11(𝜃,𝜑)𝜋
0
2𝜋
0sin 𝜃𝑑𝜃𝑑𝜑 ∫ ∫ 𝐴22(𝜃,𝜑)
𝜋
0
2𝜋
0sin 𝜃𝑑𝜃𝑑𝜑
(6)
where Amn=XPRE0,m(0,ϕ) E*0,m(0,ϕ)+ E0,m(0,ϕ) E*
0,n(0,ϕ), in which E represent the
electric far field of the antenna (m,n=1,2 but m ≠ n). It is noticed that the computed
ECC satisfies the criteria of ρe< 0.5 and P1 ≅P2 , which show good diversity gain
can be obtained.
5.2 Effective Diversity Gain (EDG):
The next significant antenna diversity parameter is apparent diversity gain
(Gapp) and is given in terms of correlation coefficient [7],
Gapp = 10*ep (7)
Where 10 is the maximum apparent diversity gain at the 1% probability level with
selection combining and ep is the diversity gain reduction factor due to correlation
between the signals on the antennas. The eρ is given by [8],
29
eρ = √1 − |𝜌𝑒|2 (8)
The apparent diversity gain which is based on selection combining w.r.t %
distribution level does not include the antenna total efficiency. So we cannot
achieve effectiveness of diversity capability without considering antenna efficiency
into account. The EDG of antenna system is calculated by multiplying the apparent
diversity gain with total antenna efficiency.
5.3 Mean Effective Gain (MEG):
In the multi path propagation environment, Meg defined as the ratio between
the mean received power of antennas over a random route and the total mean
incident power at the antenna element [9],
𝑀𝐸𝐺 = ∫ ∫𝑋𝑃𝑅 . 𝐺𝜃𝑖(𝜃,𝜑) .𝑃𝜃(𝜃,𝜑)+ 𝐺𝜑𝑖(𝜃,𝜑) .𝑃𝜃𝜑(𝜃,𝜑)
1+𝑋𝑃𝑅
𝜋
0
2𝜋
0sin 𝜃𝑑𝜃𝑑𝜑 (9)
where XPR represents the cross-polarization ratio, Gθ and Gφ the power gain
patterns, and Pθ and Pφ are the θ and ϕ components of angular density functions of
the incident power, respectively. Where I,j = 1,2 and I ≠ j.
The distributions of the angular density functions are depend on the
surrounding environment. In this proposed paper, Pθ and Pφ are assumed to be in
elevation and uniform in azimuth, and are given by,
30
𝑃𝜃(𝜃, 𝜑) = 𝐴𝜃 [−{𝜃−(
𝜋
2−𝑚𝑣)}
2𝜎𝑣2 ] , (0 ≤ 𝜃 ≤ 𝜋) (10)
𝑃𝜃(𝜃, 𝜑) = 𝐴𝜃 [−{𝜃−(
𝜋
2−𝑚𝑣)}
2𝜎𝑣2 ] , (0 ≤ 𝜃 ≤ 𝜋) (11)
where mv, mH are, respectively, the mean elevation angles of each vertically-
polarized (VP) and horizontally-polarized (HP) wave distribution observed from
horizontal direction and vertical direction, respectively and σvand σH are
respectively, the standard deviations of each VP and HP wave distribution. Aθand
Aϕ are constant and determined by,
∫ ∫ 𝑃𝜃(𝜃, 𝜑)𝜋
0
2𝜋
0sin 𝜃𝑑𝜃𝑑𝜑= ∫ ∫ 𝑃𝜃(𝜃, 𝜑)
𝜋
0
2𝜋
0sin 𝜃𝑑𝜃𝑑𝜑 = 1 (12)
31
CHAPTER 6
RESULTS
The designed is simulated using a full wave electromagnetic simulator
(ANSYS® HFSS). The following parameters were obtained as result of simulation.
1. Reflection coefficient (S11) vs. Frequency
2. Transmission coefficient (S12) vs. Frequency
3. Peak Realized Gain vs. Frequency
4. VSWR vs. Frequency
Fig 6.1.S11vs frequency plot
The comparative analysis is done with respect to Reflection coefficient using
only one arm, using two arms and using two arm with neutralization line with
modified ground structure. The results are shown in above graph Fig.6.1. The
proposed antenna resonates at three frequency bands (WLAN (2.4-2.5 GHz),
WiMAX (3.4-3.8 GHz) and HiperLAN (4.7-5.8 GHz)).
32
Fig 6.2.S21 vs. Frequency
The comparative analysis is done with respect to Transmission coefficient
(S21) using only one arm, using two arms and using two arm with neutralization
line with modified ground structure. The results are shown in above graph Fig.6.2.
6.1 Effect of Ground modification:
The impedance matching and isolation are increased for all the operating
frequency bands after changing the ground structure. This is achieved by addition
of the stubs and creation of the slots on the conventional ground plane. Due to
ground modifications, the proposed antenna resonates at three frequency bands
( WLAN (2.4-2.5 GHz ), WiMAX (3.4-3.8 GHz) and HiperLAN (4.7-5.8 GHz)).
The Reflection coefficient and Transmission coefficient are shown in below.
33
Fig 6.1.1.S11 vs. Frequency plot
Fig 6.1.2.S21vs Frequency plot
34
6.2 Peak Realized Gain
Fig 6.1.3.Peak Realized Gain vs. Frequency plot
The peak realized gain of the proposed MIMO antenna is shown in Fig 6.1.3
and the gain is found to be higher as compared to that of the existing structure. Due
to mutual coupling effect, any change in one of the slot width affects the entire
characteristics. The two monopoles are same and equally placed with respect to the
symmetrical line on the PCB. The peak realized gain and total efficiency are same
for each antenna elements. The measured peak gain at port 1 is calculated to be
3.01, 3.76 and 5.26 dBi at 2.44, 3.6, and 5.2 GHz respectively.
35
6.3 Radiation pattern
Fig 6.1.4 3D Radiation pattern
Fig 6.2.1 H plane Radiation pattern
36
Fig 6.2.2 E plane Radiation pattern
Fig 6.2.3 VSWR vs. Frequency
37
Front view Back view
Fig 6.2.4.Fabricated Antenna
38
CONCLUSION
A small printed monopole diversity antenna with defected ground structure
intended for the UWB-USB dongle platform with improved gain is designed,
simulated and fabricated. The parameters such as Reflection coefficient (S11),
Transmission coefficient (S21), Radiation pattern and VSWR are analyzed and the
results are presented. From the analysis it is inferred that the proposed antenna has
improved gain and better isolation performance (below -14dB). The implication of
Defected Ground Structure and the neutralization line helps us achieve a better
isolation performance (below -14 dB). The mutual coupling between the two
antennas is reduced by using neutralization line techniques. By modifying the L-
shaped Defected ground structure we obtained the maximum gain of 5.15dB.
39
REFERENCES
1. Hari, Shalini&Manoj, “Printed monopole diversity antenna for USB dongle
applications,” Wireless personal communication, 86: 771-787.
2. Wireless LAN specification to provide significantly improved data throughput
and range, The IEEE Standard Association [On-
line].Available:http://standards.ieee.org/announcements.ieee802.11n_2009amen
d-ment_ratified.html
3. Foschini,G. J., & M.J., “On limits of wireless communication in a fading
environment when using multiple antennas,” Wireless personal communication,
6(3),311-335.
4. Su,S.-W.,Lee, C.-T., &Chang,F.-S,”Printed MIMO antenna system using
neutralization-line technique for wireless USB-dongle applications,” in IEEE
Trans. Antennas Propag.,vol.60,pp.456-463, Feb.2012.
5. Liao, W.-J.,Chang,S.-H., Yeh,J.-T., &Hsiao,B.-R., “Compact dual-band WLAN
diversity antennas on USB dongle platform”, in IEEE Trans. Antennas
Propag.,vol. 60, pp.109-117,Jan. 2014.
6. Kwon, J.,Kim, D.,Lee, Y., & Choi, J, ”Design of a MIMO antenna for USB
dongle application using common grounding, in International conference on
adv. comm. tech. (ICACT-2011), pp.313-316.
7. Li, Z., Han, M.-S., Zhao, X., & Choi, J, “MIMO antenna for wireless USB
dongle application at WLAN band”, in Asia-Pacific microwave conference,
pp.758-761, 2010.
8. Mak, A. C. K., Rowell, C. R., &Murch, R. D, “Isolation enhancement between
two closely packed antennas. IEEE Trans. Antennas propag., vol. 56, pp.3411-
3419, 2008.
9. Ansoft’s High Frequency Structure Simulator (HFSS): (online).
http://www.ansoft.com.
10. Zhang, S., Lau, B. K., Sunesson, A., & He. S, “ Closely-packed UWB
MIMO/Diversity antenna with differnet patterns and polarization for USB
40
dongle applications”, in IEEE Trans. Antennas Propag., vol.60,pp.4372-4380 ,
2012.
11. Ogawa, K., &Uwano, T, “A diversity antenna for very small 800-MHz band
portable telephones” in IEEE Trans. Antennas Propag., vol.42, pp.1342-1345,
1994.
12. T. Ohishi, N.Oodachii, S.Sekine, and H.Shoki, “A method to improve the
correlation coefficient and the mutual coupling for diversity antenna, “ in IEEE
Antennas Propag. Soc. Int. Symp. Dig., 2005, pp.507-510.
13. Taga, T, “Analysis for mean effective gain of mobile antennas in land mobile
radio environment, “ in IEEE Transactions on Vehicular Technology,vol.39,
pp.117-131, 1990.
14. Singh, H. S., Meruva, B. R., Pandey, G.K., Bharti, P. K., &Meshram, M. K,
“Low mutual coupling between MIMO antennas by using two folded shorting
strips, “, progress in Electromagnetic Research B, vol. 53, pp. 205-221,2013.
15. Karaboikis, M. P., Papamichael, V. C., Tsachtsiris, G. F., &Makios, V. T,
“Integrating compact printed antennas onto small diversity/MIMO terminals, “
in IEEE Transactions on Antennas and Propagation , vol. 56, pp.2067-2078,
2008.
16. M.Manteghi and Y. Rahmat-samii, “Multiport characteristics of a wide-band
cavity backed annular patch antenna for multi polarization operations,” in IEEE
Transactions on Antennas and Propagation, vol.53, pp.3239-3250, 2006.
17. S. W. Su, “High-gain dual-loop antennas for MIMO access points in the
2.4/5.2/5.8 GHz bands,” in IEEE Transactions Antennas and Propagation,”
vol.58, pp.2414-2419, 2010.
18. C.C. Hsu, K. H. Lin, and H. L. Su, “Implementation of broadband isolator using
metamaterial-inspired resonators and a T-shaped branch for MIMO antennas,”
IEEE Transactions Antennas and Propagation, vol.59, pp.3936-3939, 2011.
19. K. C. Lin, C. H. Wu, C. H. Lai, and T. G. Ma, ”Novel dual band decoupling
network for two element closely spaced array using synthesized micro strip
line,” in IEEE Transactions Antennas and Propagation, vol.60,pp.5118-5128,
2012.
41
20. J. F. Li, Q.X Chu, and T. G. Huang, “A compact wideband MIMO antenna with
two novel bent slits, “ in IEEE transactions Antennas and Propagation, vol. 60,
pp. 482-489, 2012.
21. A. Diallo, C. Luxey, P.L. Thuc, R. Staraj, and G. kossivas, “Enhanced two-
antenna structures for universal mobile telecommunication system diversity
terminals, “ IET Microw. Antennas Propags.,vol.2, pp.93-101, 2008.
22. A. Diallo, C. Luxey, P.L. Thuc, R. Staraj, and G. Kossivas, “Study and
reduction of mutual coupling between two mobile phones PIFAs operating in
the DCS1800 and UMTS band, “ IEEE Trans. Antennas Propags., vol.54,
pp.3063-3074, 200.