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

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