DEVELOPING A COMPACT BANDPASS FILTER USING A …

FACULTY OF ENGINEERING AND SUSTAINABLE DEVELOPMENT .

DEVELOPING A COMPACT BANDPASS FILTER

USING A METAMATERIAL FOR RGSM-900

Ahmad Ejaz

January 14, 2013

Master’s Thesis in Electronics

Master’s Program in Electronics/Telecommunications

Examiner: Prof. Daniel Rönnow

Supervisor: Dr. Jenny Ivarsson

Ahmad Ejaz DEVELOPING A COMPACT BANDPASS FILTER USING A METAMATERIAL FOR RGSM-900

i

Abstract

Metamaterials have a wide range of potential uses in areas such as optics, transmission lines,

communication and RF design. The simplest metamaterial structures are composite right/left

handed transmission line(CRLH TL)T-structures, Split-Ring Resonators (SRR) and

Complementary Split-Ring Resonators (CSRR). Through the combination of various forms of

these structures, different performances can be achieved.

In this thesis depth investigation was performed on a metamaterial transmission line that was

realized through microstrip filter using composite right/left-handed transmission line (CRLH

TL) metamaterials. The filter was designed in the band, Railways GSM-900 (915.4 MHz –

921 MHz), and then compared with the conventional filter, because designing a metamaterial

filter is simple with considerable size reduction and improved results.

In this thesis the behavior of different parameters and their impact on the filter performance is

also investigated.

Different filters were designed by using different substrates including Rogers 5880 , Rogers

3010, Arlon 25 FR, and FR4 having different dielectric constant, thickness and loss tangent to

see their impact.

Finally, a band pass filter was designed at required frequency(915.4 MHz – 921 MHz)

through EM- simulation. The simulated values are presented and show required results.

Metamaterial filters are useful in many communication applications because they have

compact size, low loss, good performance and are cost effective.


ii

Acknowledgements

The author would like to thank the following persons:

His supervisor Dr. Jenny Ivarsson, for guidance and assistance.

His examiner Prof. Daniel Rönnow for guidance and technical ideas to make this

project better.

Mr. Efrain Zenteno for help in the fabrication knowledge.


iii

List of abbreviations and Symbols

R-GSM Railways GSM

ADS Advanced Design System

BPS Band Pass Filter

EM Electromagnetic Simulator

CRLH Composite Right-left Handed

LCP Liquid Crystal polymer

TL Transmission Line

SRRs Split Ring Resonators

CSRRs Complementary Split-Ring Resonator

LH Left Handed

MIC Microwave Integrated Circuit

MMIC Monolithic Microwave Integrated Circuits

HMDS Hexamethyldisilazane

Ɛr Dielectric Constant

S11 Reflection coefficient

S21 Transmission coefficient


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List of Figures Page

Figure 2.1 : Transmission line model of an infinitesimal length ΔZ 5

Figure 2.2 : (a) Model of right-handed line, 6

(b) Model of left-handed line, 6

(c) Model of composite right/left-handed line 6

Figure 2.3: CSRR equivalent circuit model 8

Figure 2.4: SRR equivalent circuit model 8

Figure 4.1: The layout of the microstrip bandpass filter using CRLH Transmission line and its 12

equivalent electrical circuit

Figure 4.2: (a) Schematic for 1-Cell using Rogers 3010 (for h= 5.080 mm) 15

(b) Simulation Result for 1-Cell using Rogers 3010 (for h= 5.080 mm) 16

Figure 4.3: Simulation Result for 1-Cell using Rogers 3010 (for h= 1.524 mm) 17

Figure 4.4: (a) Schematic for 1-Cell using Rogers 5880 18

(b) Simulation Result for 1-Cell using Rogers 5880 18

Figure 4.5: Simulation Result for 1-Cell using Rogers 5880(for h= 5.080 mm) 19

Figure 4.6: Simulation Result for 1-Cell using Arlon 25 FR(h=1.4732 mm) 21

Figure 4.7: Simulation Result for 1-Cell using FR4(h=1.4732 mm, tan D= 0.0009) 22

Figure 5.1: ADS generated single cell Mesh layout 25

Figure 5.2: Substrate layer by using material Rogers_RT_5880 26

Figure 5.3: Shifted EM simulation result for S21 27

Figure 5.4: Shifted EM simulation result for S11 28

Figure 5.5: Required EM simulation result for S21 28

Figure 5.6: Required EM simulation result for S11 29

Figure 5.7: ADS 3-D Preview 29

Figure 5.8: Far field visualization 30

Figure 5.9: Filter Layout for fabrication 30


v

List of Tables

Table Page

1 default dimensions of the CRLH TL BPF 14

2 layout dimensions of the CRLH TL BPF 25

3 Fabrication dimensions of the CRLH TL BPF 31


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Table of contents

Abstract .................................................................................................................................................... i

Acknowledgements ................................................................................................................................. ii

List of abbreviations and Symbols ....................................................................................................... iii

List of Figures ...................................................................................................................................... iv

List of Tables ........................................................................................................................................... v

Table of contents .................................................................................................................................... vi

CHAPTER 1 ............................................................................................................................................ 1

Introduction ......................................................................................................................................... 1

1.1 Background .................................................................................................................................. 1

1.2 Objective ....................................................................................................................................... 2

CHAPTER 2 ............................................................................................................................................ 3

Literature Review ................................................................................................................................ 3

2.1. Substrates ..................................................................................................................................... 3

2.1.1. Rogers .................................................................................................................................... 3

2.1.2. LCP ........................................................................................................................................ 3

2.1.3. Polyimide............................................................................................................................... 4

2.2 Right-handed and Left-handed Metamaterial Theory .................................................................. 4

2.2.1 Transmission line theory model ............................................................................................. 5

2.3. Metamaterial Structures: .............................................................................................................. 7

2.4. Flexible Metamaterials ................................................................................................................. 9

2.5. Fabrication techniques .................................................................................................................. 9

CHAPTER 3 .......................................................................................................................................... 10

Equipment and Software ................................................................................................................... 10

3.1.Simulation and Data Analysis ..................................................................................................... 10

3.1.1. Agilent ADS 2011 ............................................................................................................... 10

CHAPTER 4 .......................................................................................................................................... 11

Research Methodology and Designing the CRLH Metamaterial band pass filter ............................. 11


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4.1.Layout structure using CRLH Transmission line ........................................................................ 11

4.2. Transmission Line ...................................................................................................................... 13

4.3.Substrate Selection ...................................................................................................................... 13

4.4.Design and Simulations ............................................................................................................... 14

4.4.1.Rogers 3010 .......................................................................................................................... 14

4.4.2. Rogers 3010 with h=1.524 mm ........................................................................................... 16

4.4.3. Rogers 5880 ......................................................................................................................... 17

4.4.4. Rogers 5880 with incresed thickness .................................................................................. 19

4.4.5.Arlon 25 FR and FR4 ........................................................................................................... 20

4.5.Results & Discussion: ................................................................................................................. 22

CHAPTER 5 .......................................................................................................................................... 24

Momentum Simulation ...................................................................................................................... 24

5.1.Layout generation: ....................................................................................................................... 24

5.2.Substrate subscription: ................................................................................................................ 26

5.3.Port and Frequency Subscription: ............................................................................................... 27

5.4.Simulation results: ....................................................................................................................... 27

Discussion and Conclusions: ................................................................................................................. 32

References: ............................................................................................................................................ 33


1

CHAPTER 1

Introduction

1.1 Background

Metamaterials are structures that are relatively new in the scientific field. These structures

have particular behavior that is not commonly found.They exhibit negative permittivity and

permeability over small frequency ranges[2], which can result in backward propagation of

travelling waves. Due to these properties, several new applications are possible.

Metamaterials can be useful in RF,the optical world, communication, radar, environmental

remote sensing, military and medical systems, i.e. the majority of applications of today´s

microwave technology[4]. The most well known area where metamaterials are useful is for

invisibility cloaks, which is still being heavily researched, through extra polation,

metamaterial 3D cloaks could be constructed on LCP and not change resonance frequency

while contorted . This would prove useful for a real-world 3D invisibility cloak[2].

Another area in which metamaterials can prove useful is in transmission line applications.

This application includes filters, sensors, and power dividers. Most of the research is being

performed on substrates like Rogers and LCP.

Microwave filters play an important role in wireless and communication systems like satellite

and cellular mobile networks. In this type of systems some designing factors of microwave

filters are important. Compactness, steepness, low cost, light weight, small size, good

performance, low loss are important parameters that are desirable to have, to enhanced system

performance and to reduce the fabrication cost[4].

GSM (Global System for Mobile Communications), is the world´s most widely used cellular

phone technology. Different frequency bands are designed for the operation of GSM.

GSM-900 is used in most parts of the world including Europe.In Sweden GSM-900 is used

for Railways at frequency (915.4 MHz – 921 MHz) [23].

R-GSM is Railways Global system for mobile communications, its an international wireless

communications standard for railways communication and applications- A sub-system of

European Rail Traffic Management System, it is used for communication between train and

railway regulation control centres. It guarantees performance at high speeds without any


2

communication loss. R-GSM uses a specific frequency band (915.4 MHz – 921 MHz),

however R-GSM can operate on a number of frequencies that are being used around the world

[23].

1.2 Objective

The objective of this thesis is to develop a compact steep narrow band filter at a particular

frequency by using a suitable metamaterial structure by applying CRLH TL(Composite

right/left handed transmission lines) applicable for RGSM (Railways GSM-900).

Metamaterial filters have been constructed on different substrates, especially on Rogers and

LCP. They have shown not to change resonance frequency while being contorted at extreme

bends.

To achieve the objective, the following steps are applied:

1. Design a steep high performance compact micro strip filter for RGSM by using CRLH

TL technique.

2. Simulate and investigate frequency response of filter using an Electromagnetic

simulator software (ADS).

3. Simulation is carried by using different substrates at frequency 915.4 – 921 MHz and

optimized result is obtained .

4. Compare the metamaterial filter with a conventional filter.


3

CHAPTER 2

Literature Review

In this chapter, types of substrates, the basic concepts of metamaterials, Right-handed and

Left-handed material theory ,metamaterial structures, flexible metamaterials and fabrication

techniques are discussed. The most common substrates used are rigid such as Rogers

substrates.

Some basic structures of metamaterials known as SRRs (Split Ring Resonators) and CSRRs

(Complementary split ring resonators) are also discussed. Next, flexible metamaterials and

common flexible substrates are introduced.Two of these flexible substrates are Liquid Crystal

Polymer (LCP) and polyimide. Finally, common available fabrication techniques will be

overviewed.

2.1. Substrates

Metamaterial structures are designed for different frequency applications. The frequencies

may range from MHz to GHz and up to THz. With such a wide range of frequencies , special

compatible substrates must be used. The most common substrate is usually rigid since rigid

substrate fabrication techniques have been perfected for many years. Below, several types of

substrates commonly used in conjuction with metamaterials are discussed.

2.1.1. Rogers

Rogers substrates are designed for performance sensitive and high volume applications [19].

Rogers corporation fabricates laminates for different frequencies. Different Rogers substrates

are used for different applications. Rogers5880, Rogers R03010 are used in multiple

applications for metamaterials because of their frequency reliability [7] . Rogers boards are

mainly available with dielectric constant of 2.20 and 10.2 and comes in varying heights from

a manufacturer. These heights are much thicker than their flexible counterparts.

2.1.2. LCP

LCP is a fairly new thermoplastic organic material and is less common among the

metamaterial world but has some advantages over Rogers laminates. The main advantage is

flexibility and resistance to moisture absorption [18] .Flexibility proves useful in certain


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scenarios such as 3-D invisibility cloak. When purchased from a manufacturer, LCP already

has either one or both sides laminated with copper foil and has a relative permittivity of 3.1

[20]. Wet and dry processes to etch through LCP are also known. Etching copper on LCP can

be treated similarly to a rigid substrate with feature sizes around 100 micrometer or smaller if

a backing wafer is used.

2.1.3. Polyimide

Polyimides are polymers composed of imide monomers. Polyimides are also less common

among the metamaterial world along with LCP. Polyimides are more costly than LCP and

operate at high frequencies reliably, normally at terahertz frequencies. Additionally,

polyimides can be deposited onto a substrate [8]. Similar to LCP, some polyimides can also

be dry etched.

2.2 Right-handed and Left-handed Metamaterial Theory

Conventional and CRLH (Composite right-left handed) materials have a characteristic in

common, because of structural restriction. Basically, the CRLH structure is smaller than a

quarter of a wave length [22], so it is possible to make an equivalent circuit using an inductor

or a capacitor.

To explain theoretically through vector positioning, it can be said that considering E

, H

and

S

vectors which follow the right-handed rule in nature ( S E H

), metamaterials follow the

left handed direction [8]. S

indicates the pointing vector perpendicular to the electric vector (

E

) and magnetic field vector ( H

). In right-handed materials, the direction of the S

vector is

given by the direction of movement of a right-handed screw when it rotates in the direction of

from electric field vector ( E

) to the magnetic field vector ( H

). But the direction of S

in left-

handed materials is in the opposite direction ( E H

) [23] . Mathematically this leads to

negative permittivity (ε) and negative permeability (μ), hence in right-handed materials group

velocity and phase velocity are in the same direction whereas in left-handed materials they are

in the opposite directions.

TL theory has long been a powerful analysis and design tool for conventional (RH) materials.

By modeling a CRLH metamaterial as an equivalent TL, TL line theory can be used to

analyze 1,2 or even 3-D CRLH metamaterials [22].


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To develop a TL approach to CRLH, first the CRLH metamaterial will be represented by an

equivalent homogeneous CRLH TL to gain immediate insight into its fundamental

characteristics. Then an LC network implementation of the TL will be developed , since

homogeneous CRLH structures do not exist in nature . The LC network provides a realistic

description of the CRLH metamaterial.

2.2.1 Transmission line theory model

In electrical engineering wave propagation can be modeled by transmission line theory.

Therefore it is possible to represent both right-handed and left-handed materials by a

transmission line [11] [6]. Fig. 2.1 illustrates a general form of a transmission line model for

an infinitesimal length ΔZ.

Fig.. 2.1 : Transmission line model of an infinitesimal length ΔZ [6].

This model consists of a distributed series impedance, Z Ohms/m and a shunt admittance, Y

Siemens/m. The characteristic impedance, Z0 and the phase constant, β of a lossless

transmission line are expressed as;

0

ZZ

Y (1)

j ZY (2)

According to this concept it will be shown that a purely RH (PRH), purely LH(PLH), and

CRLH lossless transmission line can be modeled as illustrated in Fig. 2.2(a), (b), and (c)

respectively.


6

Fig. 2.2 : (a) Model of right-handed line, (b) Model of left-handed line, (c) Model of

composite right/left-handed line [6].

In Fig. 2.2(a) the series impedance part is an inductance, L and the shunt admittance is a

capacitance, C.

Therefore noting that

Z j L (3)

Y j C (4)

By substituting in equations (1) and (2);

0

LZ

C (5)

LC (6)

By the definition the phase velocity is defined as;

1

LC

(7)

Consequently the group velocity will be;

1d

d LC

(8)

As can be seen, the group velocity and phase velocity both have the same sign and therefore

are in the same direction and as stated before this represents a right-handed material [6] . In

the same way it can be shown that Fig. 2.2(b) represents a left-handed material because;


7

0

LZ

C (9)

1

LC

(10)

Hence the phase velocity and group velocity become

2 LC

(11)

2dLC

d

(12)

It can be seen here that the phase velocity and group velocity have different sign and therefore

point in different direction. Hence this represents a left-handed material.

In Fig. 2.2(c) the composite right/left-handed material consists of a combination of an

inductance and capacitance in both the series and shunt parts. This structure can work as a

bandpass filter. This is the desired structure which will be applied in this project to constitute

a bandpass filter.

2.3. Metamaterial Structures:

There are two common basic metamaterial structures. They are the Split-Ring Resonator

(SRR) and the Complementary Split-Ring Resonator (CSRR) [3]. There are derivations of

each structure, such as edge coupled (EC-SRR) or broadside coupled (BC-SRR) . Each of

these structures can be represented by equivalent circuit models and are shown in Fig. 2.3 and

2.4 . In the figures, L and C represent the per-unit inductance and capacitance of the line. Cg

is the gap capacitance across the transmission line. Cc and Lc are the capacitance and

inductance of the rings for a CSRR. Ls’ and Cs’ represent the mutual inductance and

capacitance of a SRR.


8

Fig. 2.3: CSRR equivalent circuit model [3]

Fig. 2.4: SRR equivalent circuit model [3]


9

2.4. Flexible Metamaterials

Flexible metamaterials have been introduced onto polyimide and kapton layers. The use of

standard photolithography with a backing wafer could be used in some cases in order to

obtain smaller feature sizes of several microns [8]. In other cases, polyimide and any metals

needed for fabrication were deposited [21].

2.5. Fabrication techniques

The vast majority of published metamaterial oriented papers use standard photolithography

processes. Only a few differences occur. One of these differences is either buying prebuilt

substrates or deposition of a substrate onto a silicon wafer [8]. Another difference was the use

of a backing wafer to obtain significantly smaller feature sizes on a flexible substrate [21].


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CHAPTER 3

Equipment and Software

In this chapter, laboratory software is described. Software will be presented in the order in

which it was needed in design.

3.1.Simulation and Data Analysis

The following programs were used to simulate a design, layout a design, or plot that has been

gathered.

3.1.1. Agilent ADS 2011

Agilent ADS, a commercially available electromagnetic simulation software package, proved

to be a useful tool. One part of ADS that was particularly useful was LineCalc. LineCalc

provided a calculator that could calculate impedance based off of line width, substrate

thickness, relative permittivity of substrate, copper thickness, and frequency. This was useful

for the impedance matching that was necessary for high frequency applications. The other

useful part of ADS was Momentum. Momentum provides a method-of-moments full wave

simulation. This involves performing calculations based on Maxwell’s equations for every

cell in a mesh that was defined by the user. This provided an overall more accurate simulation

than simulations with discrete components like resistors and capacitors.


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CHAPTER 4

Research Methodology and Designing the CRLH Metamaterial

bandpass filter

In this chapter the methods used for designing, the layout structure and design concepts are

reviewed. Transmission line calculation and generation of layout for the EM simulation are

discussed.

4.1.Layout structure using CRLH Transmission line

The layout of the bandpass filter using CRLH transmission line is depicted in Fig.4.1 The

filter structure will be fed after the transmission line by using the gap coupling method in

which the input and output ports are spaced symmetrically with a gap on each side. Gap

coupled microstrips give a large bandwidth as compared to conventional microstrips without

gaps. By adjusting the gap and various dimension parameters of the gap coupled microstrips,

the bandwidth can be enhanced [17].


12

Fig. 4.1 : The layout of the microstrip bandpass filter using CRLH Transmission line and its equivalent electrical circuit [16].


13

4.2. Transmission Line

Attached to Agilent ADS, there is a program called LineCalc. LineCalc was an essential tool

for designing impedance matched lines. To design a 50Ω impedance matched line, the

following parameters were changed: the relative permittivity, height of the substrate,

frequency, the thickness of the metal and dielectric constant. Once those values were inserted,

the setup was tested and the line width, W, was updated. The line width yielded was the line

width needed for the transmission line. For the designs , εr = 2.20, h = 5.080 mm, Frequency,

f = 918.2 MHz, and Z0 = 50Ω were the input parameters which yielded that the width of the

copper trace. These parameters were used for the transmission line and was added in the

layout designed for manufacturing. These optimized values are valid for any 50Ω impedence

matched line and can be used in all the simulations in ADS.

4.3.Substrate Selection

In this section the selection of a suitable substrate according to the requirements by keeping

the compactness of the filter and cheapness by means of price, is presented.

The substrates that were selected to get the required result are given below.

1) Rogers 3010 (Ɛr = 10.2 ,tan(δ) = 0.0035, h=5.080 mm)

2) Rogers 3010 (Ɛr = 10.2 , tan(δ) = 0.0035, h=1.524 mm)



5) Arlon 25 FR (Ɛr = 3.48 , tan(δ) = 0.0035, h=1.4732 mm)

6) FR4 (Ɛr = 4.6 , tan(δ) = 0.01, h=1.4732 mm)

The effect of using the different substrates with different thickness,h, loss tangent ,tan(δ), and

dielectric constant, Ɛr , is discussed in the results at the end of the chapter.


14

4.4.Design and Simulations

By using the above explained structure, the bandpass filter is designed and simulated to get

the acceptable required result at required frequency with good performance including a low

insertion loss in the pass band and high return loss.

For this purpose different above mentioned substrates were used.The details are given below

for each substrate used.

4.4.1.Rogers 3010

The layout of the bandpass filter using CRLH transmission line is fed by using the gap

coupling method in which the input and output ports are spaced symmetrically with a gap on

each side.

The dimensions of different parts of the metamaterial structure used in Fig. 4.1 are shown in

table 1. These dimensions can be selected as the default dimensions for starting to design

another filter, operating at different frequency.

Table 1: default dimensions of the CRLH TL BPF

Parameter Dimension

W1 2 mm

W2 2 cm

W3 5 mm

g 0.3 mm

l1 1 mm

l2 2.6 mm

l3 1 mm

l4 5 mm


15

This structure was simulated by means of ADS and the simulation result along with the

schematic using Rogers 3010 specifications with Ɛr = 2.20 , tan(δ) = 0.0035 and h = 5.080 is

shown in the Fig4.2 (a), (b). below.

Fig.4.2. (a) Schematic for 1-Cell using Rogers 3010 (for h= 5.080 mm).


16

Fig.4.2.(b) Simulation Result for 1-Cell using Rogers 3010 (for h= 5.080 mm).

As can be seen from the figure the bandpass filter operating at centre frequency 918.2 MHz is

obtained,but the return loss is acceptable(-16 dB) and the insertion loss is bit different (-1.532

dB), as it should be approximately -0.5 dB for better performance [22]. But the main problem

is required bandwidth (915.4 MHz – 921 MHz) , which is not fulfilled, as it is more than the

required 5.6 MHz (915.4 MHz – 921 MHz).

4.4.2. Rogers 3010 with h=1.524 mm

The simulation result by using substrate Rogers 3010 with dielectric constant ,Ɛr = 2.20, loss

tangent ,tan(δ) = 0.0035 and thickness ,h , of 1.524 mm is shown in the Fig. 4.3 below.


17

Fig.4.3. Simulation Result for 1-Cell using Rogers 3010 (for h= 1.524 mm).

It is seen from the figure that at the required centre frequency 918.2 MHz the performance is

not acceptable. The insertion loss(-3.285 dB) is very high and the return loss (-9 dB) which is

very low .

The bandwidth is 8.2 MHz which is also more than the required 5.6 MHz for the Railways

GSM-900 (915.4 MHz – 921 MHz).

4.4.3. Rogers 5880

The simulation result by using Rogers 5880 with dielectric constant, Ɛr, 2.20, loss tangent ,

tan(δ) , 0.0009 and thickness, h ,of 1.524 mm is shown along with the schematic in the Fig.

4.4(a),(b) below.


18

Fig. 4.4. (a) Schematic for 1-Cell using Rogers 5880.

Fig.4.4.(b) Simulation Result for 1-Cell using Rogers 5880.


19

As can be seen from the figure the desired bandpass filter operating at centre frequency 918.2

MHz is obtained,and the return loss is acceptable(-11 dB) along with the improvement in the

insertion loss. But the main problem is required bandwidth (915.4 MHz – 921 MHz) , which

is not fulfilled.

The bandwidth can be increased by using cascaded cells but in this way the size will be

increased along with the reduction in the performance, which is not desired.

4.4.4. Rogers 5880 with incresed thickness

Thickness of the substrate was increased from 1.524 mm to 5.080 mm. The simulation result

by using substrate Rogers 5880 with dielectric constant 2.20, loss tangent 0.0009 and

thickness of 5.080 mm, is shown in the figure 4.5 below.

Fig. 4.5 Simulation Result for 1-Cell using Rogers 5880(for h= 5.080 mm).


20

As can be seen from the figure the desired bandpass filter operating at centre frequency 918.2

MHz is obtained with the exact required band width 5.6 dB (915.4 MHz – 921 MHz). The

desired bandpass filter has a good performance including a low insertion loss(-0.873 dB) in

the passband and good return loss(-21 dB).

4.4.5.Arlon 25 FR and FR4

In the previous section it was found that a filter on substrate Rogers 5880 fulfills the technical

requirement, but as we aimed at creating a compact but cost effective band pass filter for

RGSM-900, the substrates Arlon 25FR and FR4 were investigated for the following reasons.

1) Arlon 25 FR is low loss material and cheaper than the Rogers substrates.

2) Standard FR4 with the same size and thickness (5.080 mm) is very cheap compared to

the Rogers substrates, but it is very lossy dielectric.

4.4.5.1. Arlon 25 FR

By using the Arlon 25 FR with the parameters Ɛr = 3.48 ,tan(δ) =0.0035, h=1.4732 mm,

the result obtained is shown in the Fig. 4.6 below.


21

Fig.4.6.Simulation Result for 1-Cell using Arlon 25 FR(h=1.4732 mm).

The result obtained as seen in the Fig.4.6 is poor in terms of return loss (S11 = -2 dB ) and

insertion loss (S21 = -7.119 dB ) which is required -15 dB and -0.5 dB respectively for

acceptable performance, the return loss and insertion loss was improved by increasing the

thickness `h` of the substrate but Even then required band width ( 5.6 MHz ) was not

fulfilled.

4.4.5.2. FR4

By using the FR4 with the parameters Ɛr = 4.6 , tan(δ) = 0.01, h=1.4732 mm, it is very

difficult to get the required results even if we use the same thickness 5.080 mm used

previously. The required result were not found but an intersting point was that,with these

values we can get a very good result at high frequencies e.g. at 6-7 GHz.The result for 6.3

GHz is shown in the Fig. 4.7 .


22

Fig.4.7.Simulation Result for 1-Cell using FR4(h=1.4732 mm, tan D= 0.0009).

4.5.Results & Discussion:

The results of the simulations are summarized here.

1) The required filter specifications are obtained by using the Rogers 5880 substrate with

dielectric constant ( Ɛr = 2.20 ), loss tangent ( tan(δ) = 0.0009 ) and thickness `h` of

5.080 mm.

2) By using different substrates with different parameters, the behaviour of these

parameters including tan(δ) (loss tangent), Ɛr (Dielectric constant), and `h´ (laminates

thickness) was observed as follows.

i) A change in “tan(δ)” changes the value of S11 and S21. The smaller the value of

tan(δ) the better will be the result. The higher the value of tan(δ) the poorer the

result in terms of S11 and S21.


23

ii) A change in “Ɛr” makes shift in the frequency. A smaller value of , Ɛr ,shifts

the centre frequency (918.2 MHz) to higher value and higher value of, Ɛr ,shifts

the centre frequency backwards, if the stublengths are kept constant.

iii) The substrate thickness “h” is the most important parameter for the

performance. By increasing the thickness we can get improved results with low

insertion loss and high return loss. It can be said that laminates thickness and

size are the most important parameters to make the filter cost effective.


24

CHAPTER 5

Momentum Simulation

Momentum simulation (EM simulation) were carried out in order to generate the layout for

the chosen structure, as obtained in the previous chapter.

Since RF component designs are becoming more compact , proximity effects between

components are becoming more pronounced and have significantly more impact on the

performance.For this reason,EM simulations are required and included in the overall design

process.

EM simulations benefit in efficient meshing, adaptive frequency sampling which reduces

simulation time.The EM simulator is also able to simulate complex EM effects including skin

effects, substrate effects, thick metals and multiple dielectrics.

The steps involved in this chapter include, generation of layout, allocation of substrate

layer,allocation of conductor layer, fixing of ports, subscription of frequency plan, simulation

of generated layout and confirmation of the required performance in terms of return loss and

insertion loss.

5.1.Layout generation:

The required results were obtained by using Rogers 5880 substrate( h= 5.080 mm),which is

chosen for the layout. The layout is generated using EM simulation and is shown in Fig 5.1.


25

Fig.5.1: ADS generated single cell Mesh layout

The dimensions of generated layout are given below in the table 2.

Table 2 :layout dimensions of the CRLH TL BPF

Parameter Dimension

W1 5 mm

W2 2.5 cm

W3 5 mm

g 0.5 mm

l1 1 mm

l2 5 mm

l3 1 mm

l4 5 mm


26

5.2.Substrate subscription:

To start the EM simulation a substrate was subscribed.The subscription is shown in the figure

5.2.

Fig.5.2. Substrate layer by using material Rogers_RT_5880

The parameter values used for substrate layer are,

Thickness : 5.08 mm

Material : Rogers_RT_Duroid5880

Ɛr real : 2.20

tan(δ) : 0.0009

tan(δ) Frequency : 10 GHz

Low Frequency : 1 kHz

High Grequency : 1 THz

The next step is to fix the conductor layer, 1 onz ( 35 micron )of copper was used.


27

5.3.Port and Frequency Subscription:

To proceed further the input and output ports were fixed. By default these get converted to 50

ohms ports.

Now frequency plan was selected for the range 0 – 2 GHz to get the simulation result at

desired RGSM frequency.

5.4.Simulation results:

After completing the simulation, the results obtained are shown below in the figure 5.4 and

5.5 for S21 and S11 respectively in terms of phase and magnitude.

Fig.5.3: Shifted EM simulation result for S21


28

Fig.5.4: Shifted EM simulation result for S11

It can be seen that the result is shifted as compared to what was expected, so different

parameters were varied including the stub lengths, gaps and via holes to get the required

results.

After fixing the stub lengths and gap the result which fulfills the specifications was

obtained.The results are shown below in the figure 5.6 and 5.7 for S21 and S11 respectively

in terms of phase and magnitude.

Fig.5.5: Required EM simulation result for S21


29

Fig.5.6: Required EM simulation result for S11

As can be seen from the above figure good performance is obtained at the required GSM-900

frequency for return loss and insertion loss.

In Figure 5.8 software generated 3-D views of the layout is shown.

Fig.5.7 : ADS 3-D Preview

Furthermore we can compute the far field from the simulation results of the current EM setup

as shown in the Fig. 5.9 below.


30

Fig5.8: Far field visualization

The final filter layout for the manufacturing is shown below in the figure5.10.

Fig5.9: Filter Layout for fabrication


31

The dimensions of the filter are given below in table 3, according to the parameters used in

figure 4.1.

Table3 : Fabrication dimensions of the CRLH TL BPF

Parameter Dimension (mm)

W1 5 mm

W2 3.1 cm

W3 5 mm

g 0.5 mm

l1 1 mm

l2 5 mm

l3 1 mm

l4 5 mm


32

Discussion and Conclusions:

The aim of the project “Developing a compact bandpass filter using metamaterial structure

for RGSM-900” was achieved.The required filter specifications are obtained at centre

frequency 918.2 MHz by using the substrate Rogers 5880.The simulation results also show

that the substrate material with higher thickness gives a more compact structure with low

insertion loss and high return loss.

In comparison with the conventional filters, designing filter using CRLH metamaterials is

simple due to easy structures. In addition metamaterial structures enhance the performance

along with a remarkable size reduction as compared to conventional filters, varies from filter

to filter and ranges from 30 % to 80 % [8].

In this CRLH design 1-cell type by using Rogers 5880 as the substrate material , minimum

insertion loss along with return loss of -18 dB at centre specified frequency 918.2 MHz using

EM simulation is obtained which is the expected result of a manufactured filter.

This proposed bandpass filter has a total dimension of 4.2 cm × 2 cm , which is considerable

compact size as compared to conventional filters, cavity filter operating at 900 MHz

frequency range has size upto 11 inches, which makes it very useful in different applications.


33

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