chapter-1 introduction -...

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CHAPTER-1

INTRODUCTION

1.1 Tunable Microwave Devices : Need of the future

Spectacular progress has been witnessed in the last two decade in microwave

technology in almost every domain from military to civilian areas like safety and

security systems, wireless sensor networks, medical and environmental sensors,

food monitoring, radio etc. However, the progress made and challenges faced by

the modern society indicates that in the future these systems such as cellular and

satellite communication systems, mobile navigation devices radar, wireless

global and local area network systems have to be more user friendly, adaptable,

reconfigurable and cost effective [1] [2].

Tunable devices often find applications in multi-band telecommunication

systems, radiometers, wideband radar systems, and can also be used to correct

minor deviation from manufacturing errors, or to reconfigure the operating

performance and characteristic of a system. These devices contribute effectively

in optimising the cost and complexity of the system by reducing the number of

circuits for separate operating conditions. The purpose of miniaturization of

wireless devices is to reduce space and weight which is desirable in applications

where portability or high device density is required.

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This can be achieved by using tunable filters, tunable matching networks,

tunable antennas, frequency selective (tunable) switches, phase shifters etc.

1.2 Different Trends in Tuning

Current development in microelectromechanical systems (MEMS) process has

forced scientific community to think in various dimensions for the improvement

of designs and performance of these tunable devices. These devices can be tuned

electrically, magnetically or both the ways. This need can be fulfilled to a great

extent by replacing complex device with circuits made by using thick and thin

films, or by using active components such as varactor and pin diodes. There are

several techniques to improve the performance of the tunable devices [28].

These days several technologies are utilizing components-like varactors, pin

diodes, microelectronechanical systems (MEMS), ferroelectric and

ferromagnetic thin films, and metamaterials. Ample research work has been

already done in these domains. However, still the quest for better technology is

on and intense research is being carried out worldwide.

These days’ two main approaches are used to develop microwave tunable

devices:

(i) The conventional circuits having high quality factor available with the

lumped tunable components, such as varactors,

(ii) The microwave devices designed on the surface of

ferroelectric/ferromagnetic films or substrates.

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Magnetically tunable and switchable microwave devices are always in demand

in multiband systems. Tunable devices provide new functionalities and designs

for communication system with reduced size and complexity [3] [4].

In early days researchers used mechanically tunable devices, which were made

of coaxial lines or hollow metal waveguides and trimming screws. These

mechanically tuned devices were simple to use and offered low loss solutions.

But on the other hand, they were bulky, slow, costly, and sensitive to vibrations

and required high power control.

To overcome these disadvantages researchers switched to bulk ceramics, used as

substrates, to develop relatively small size and fast tunable devices.

Nevertheless, these devices were slow, sensitive to vibrations, and not suitable

for cost effective integration [2].

Semiconductor varactor and transistors are also widely used in tunable

microwave devices. They provide high density integration and are very cost

effective due to which these devices used in both commercial and defence

systems. But they do not have very high quality factor and hence consume more

power.

Recently, MEMS switches and varactors attracted considerable attention. These

devices not only offers low losses and low power control with better integration

possibility but also promise superior performance in comparison to bulk

mechanical devices [1]. In the MEMS technology, to activate the movement of

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thin metal membranes use the electrostatic force by applying DC bias between

the membrane and bottom electrode [3].

Researchers are developing different types of MEMS circuits like those that

MEMS circuits made on highly resistive substrates [8], and some of them made

on glass substrates, coupled with the transmission lines. In some microwave

devices, MEMS switches are made in arrays and these switches can be actuated

individually. They allow fine tuning and complete reconfiguration of circuits

[2].

Although the idea behind MEMS devices is very simple, but the fabrication of

MEMS based devices is not easy, because these devices require vacuum

packaging, and hence suffer from scalability problems.

An extensive research has been carried out to develop artificially fabricated

metamaterials with unique properties. Among these composite materials,

exhibiting negative permittivity and negative permeability have received much

attention in EM community [23].

Tunability in split rings or open loop resonators is mainly due to the capacitance

control of equivalent LC circuits of the SRR (Split Ring Resonators) by electric

field. In literature, various approaches were reported for metamaterial tuning

[11]. A common approach is to change the geometrical parameters or to play

with the thickness and dielectric constant of substrates, but it is not possible to

change the geometrical parameters of already printed substrate, therefore to tune

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these devices, lumped capacitors, or varactors, ferromagnetic, ferroelectric

techniques, and semiconductors techniques have been suggested in literature.

For electric tuning in the split rings, varactor diodes were placed between the

splits of the SRRs, and for magnetic tuning some of researchers attached pieces

of ferrites to the resonators, and whole resonant structure placed between

electromagnetic poles. But these devices have low quality factor and they are

not cost effective [12].

Hence, to achieve desired tuning with desired features researchers are

fabricating many devices using ferroelectric and ferromagnetic thin films.

Ferroelectric thin film based electrically tunable microwave devices are very

promising because they provide a combination of advantages such as small size,

light weight, high speed, good reliability, good tunability, very low power

consumption and low cost with low insertion loss [18]. Tunable devices using

magnetic properties of materials have a long list of applications in microwave

technology. Devices based on ferromagnetic resonance make use of the external

magnetic field to high quality resonance. In general, magnetically tunable filters

based on ferromagnetic thin films provide great selectivity and larger tuning

ranges [20]. Various research groups are also working on the deposition of thin

oxide film using nano technology. But the main disadvantage in using

ferroelectric or ferromagnetic materials for tunable devices is the relativity high

loss tangent of ferroelectric materials which leads to high microwave dissipation

[27].

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However, recent research indicates that the loss tangent can be reduced by

improved thin films fabrication methods and material enhancement such as

doping or multi layering the ferroelectric/ferromagnetic thin films. Furthermore,

with proper designed devices, it is usually possible to reduce insertion loss

through reduction in device tunability, so for satisfactory performance some

compromise can be made. Beside this, these technologies and processes are

costly and complex also [25].

Agile microwave technologies available today have the potential to facilitate

industrial scale development of the components, circuits, and systems for the

reconfigurable and adaptable microwave systems. To achieve our goal of high

performance, low cost and compact circuit size, we have a novel idea of tuning

by the ELECTROMAGNETIC BAND GAP (EBG) STRUCTURES. EBGs

have spurred enough activity amongst research groups by opening a new

horizon called Microwave Photonics.

1.3 Electromagnetic Band Gap Structures : A potential

Candidate

Deeper understanding of material properties have resulted in advancement of

technology beyond comprehension. Today, we boast of a collection of

artificially synthesized materials having range of mechanical properties with

tailored electrical properties. Advances in semiconductor physics allowed us to

tailor the conducting properties of certain material, thereby initiating the

revolution in

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transistor electronics.

In the last decade, a new frontier has emerged with similar goals: to control the

electromagnetic properties of materials. If we could engineer materials that

prohibit the propagation of EM wave, or allow it only in certain directions at

certain frequencies, or localize EM wave in specified area then the technology

would benefit.

Electromagnetic bandgap (EBG) materials are periodic structures that exhibit

wide bandpass and band rejection properties at microwave frequencies.

Introducing periodic perturbations in a material, such as dielectric rods, holes,

and patterns in waveguides and PCB substrates forms photonic bandgap (PBG)

materials. In a crystal (PC), propagation of electron is impeded by periodic

potential; similarly, electromagnetic waves in a PBG material are impeded due

to the periodic discontinuities, resulting a slow-wave structure. Currently,

researcher is also referring to the term PBG as EBG. Due to its unique

properties, EBG materials find potential applications in antennas, waveguides,

amplifiers, filters, power combining, phased arrays, and in many microwave

devices. The application of EBG engineered materials cause the suppression of

surface waves. Consequently, the performance of active and passive microwave

components and devices is enhanced. The use of EBGs in the ground plane of a

microstrip line provides attractive features. The EBG engineered microstrip line

itself shows excellent and attractive performance. EBG may have many forms

due to different possible lattice structures.

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Their behaviour can be controlled by proper choice of different lattice structures

and lattice parameters. EBG structures can be categorized as 1-D, 2-D, or 3-D.

Further, these crystals are scalable and can be applied to wide range of

frequencies [6].

These days’ researchers are working on these EBG structures to tune the

microwave devices. Some of them are using liquid- crystals-filled photonic

crystal waveguides. In this, the silicon rods were arranged in an array, in a

square lattice with the centre row rods devoid, so as to form waveguide. The

remaining space is filled with nematic LC molecules, and when the magnetic

field is applied, the device worked as magnetically tunable low-pass filter at

terahertz frequencies [8].

Muhammad Faeyz Karium and Ai Qun Ali made a tunable bandpass filter using

fractal electromagnetic band gap structures. These uniform EBG structures (U-

FEBG) were realized by replacing the etched rectangular holes with a

Minkowaski loop generator. The tunable bandstop filter was tuned by

micromachined capacitive bridge [41]. Researchers have also designed periodic

structures like split ring resonators and different types of strip line and coplanar

lines array in a periodic lattice structure on a high resistance substrate.

Finally, advantages of EBG structures can be summarized as follows:

1. Easy fabrication.

2. Low cost.

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3. Compatibility with standard circuit technologies.

4. Ability of these structures to introduce distinctive stopbands.

5. Slow-wave effect which is very important for size reduction.

6. Low attenuation in the passband.

7. Suppression of surface waves.

Nowadays, new EBG structures are being exploited everyday to reach maximum

miniaturization and minimum losses. Also, the trend towards a reconfigurable

EBG has started a couple of years ago, showing promising results. For all these

reasons, we have chosen EBG to achieve our targets.

1.4 Motivation

Microwave planar devices have been studied extensively from the advent of

microwaves during Second World War. Planar devices use microwave laminates

having very low dielectric substrate losses and small loss tangent and

conventionally used microwave substrates like single crystalline sapphire, TiO2

etc., which are very expensive but they have very low losses at microwave

frequencies.

Ground plane of planar microwave devices give rise to surface wave effect

resulting in very high thermal losses at high frequencies in an embedded

environment. But EBG structures due to their periodic discontinuity offer high

impedance to the surface propagating waves and have demonstrated lower losses

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[9-10]. This unique feature of EBG is utilized to suppress surface wave effects

in planar microwave integrated circuits.

EBG structures have been widely studied at microwave frequencies. In our

research work, it was proposed to extend these studies to various applications

where planar microwave devices are used. It is further envisioned that planar

EBG structures can render tunability due to their ability to steer EM fields.

The main focus of this research work is towards design, fabrication, and

experimentation on novel EBG lattice with nonstandard basis points and to

develop method for electromagnetic tuning.

While preparing the ground to achieve the aforementioned target, following

interim milestones were identified:

Simulation based study of planar lattice structure with different basis points

like circular patch, hexagon, & triangular patch.

Identification of method of tunability via mechanical or electromagnetic.

Develop a method for material characterization.

Materials for electromagnetic tuning and their characterization.

Present research problem has been framed after looking into the advantageous

features of EBGs and its fabrication compatibility to conventional MIC

(Microwave Integrated Circuit) technology. The work proposed herein will lead

to the development of tunable planar microwave devices using EBG structures.

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1.5 Objective

Present course of doctoral research work aim at “DESIGN, FABRICATION

AND ANALYSIS OF TUNABLE PLANAR MICROWAVE DEVICES USING

EBG STRUCTURES” with following specific objectives -

1. Theoretical analysis of planar EBGs in different lattice structures.

2. Identification of method of tunability via mechanical or electromagnetic.

3. Fabrication and analysis of tunable planar microwave devices using

planar metallo-dielectric EBG structures with high performance and low

losses.

4. Material characterization for the development of electromagnetic tuning

technique.

1.6 Literature Review

1.6.1 MEMS Tunable Microwave Devices

The MEMS technology has the potential to replace many radio frequency RF

components such as switches, inductors, capacitors, phase shifters, and ceramic

filters. Many researchers are working and already worked on this technology.

R.R Mansour and his group proposed MEMS capacitor, which was made by

using two structural layers; these were sacrificial layers and insulating layers of

nitride. In this, top plate was fabricated of nikel and covered with gold and the

bottom plate was made of polysilicon which was covered by nitride layer, and

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they etched a trench on the oxide layer. Finally, in this the tuning was achieved

by applying DC voltage [28]. C.Bozler and researchers designed a novel MEMS

switch which was capable of being configured in a multi element X-Y array for

tunable circuits. These RF micro switches were fabricated by silicon processing

techniques. The cantilever was formed from the three layers deposition of 350

nm aluminium sandwiched between two 100 nm layers of silicon dioxide [29].

Similarly, Yu. Li and his co-workers designed distributed transmission lines for

tunable filters. This tunable filter was made on a glass substrate using

capacitively coupled distributed MEMS transmission lines. This filter was tuned

at 20 GHz with low insertion loss [30]. J.Gaspers and co-workers reported a

micro electrochemical bridge resonator, which was designed on the glass

substrate with thin films and surface micromaching. These bridges were made

on silicon and aluminium, and suspended over a gate electrode [31].

Karl.M.Strohm and researchers also presents a new resonator concept in their

paper. In which they made two types of resonators, an open-end patched

resonator and a short circuit resonator on a 3D semiconductor substrate, but

these devices have low quality factor [32].

Wanling Pan and other researchers developed a highly resistive silicon-based

cylindrical resonators fabricated by micromatching technique. They worked at

the frequency range of 2.5-5 GHz. For small tuning, they fabricated a small

membrane of low SiN and coupled it with dielectric resonator, and then by

applying pressure on it, they achieved 0.6 % tuning [33]. Md. Fokhrul and

researchers designed a RF MEMS switches for tunable filters. They designed

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filter on the µm thick, highly resistive substrate, and the tuning was achieved by

the MEMS based beam shunt switches [34]. Similarly, James Brank and his co-

workers designed a MEMS based tunable filter by using RF MEMS capacitive

switches [35].

Charles L. Goldsmith and researchers designed a variable capacitor to tune a

filter. This filter was made by the bistable MEMS membrane, which was made

of silicon substrate with the buffer layer of silicon dioxide and upper layer was

of aluminium which was compatible with CMOS [36]. R.Malmquist and

researchers presents different types of reconfigurable RF MEMS based

matching networks in their paper [37].

Jin Yao and Ming. C. Wu designed a tunable add drop filters, which was based

on MEMS. This tunable filter consists of a high–Q silicon micro layered

resonator, with input and output deformable waveguides which were integrated

with two layered structure. They tuned this filter by voltage control and

achieved tunability from 2.8 GHz to 78.4 GHz [38].

Radio frequency (RF) microelectromechanical systems (MEMS) have been

perused for more than a decade as a solution of high performance on chip-fixed,

tunable, and reconfigurable circuits. A. Q. Lir and researchers reviewed the

research work on RF MEMS switches and switching circuits in the past five

years. The research work first concentrated on the development of the lateral

DC-content switches and capacitive shunt switches. Low insertion loss, high

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isolation and wide frequency band have been achieved by these two types of

switches. Then these switches have been integrated with transmission lines to

achieve different circuits, such as single pole multi throw (SPMT) switching

circuit, tunable band pass filter, tunable band stop filter and reconfigurable filter

circuits. Substrate transfer process and surface planarization process were used

to fabricate the above mention devices and circuits [39].

Insak Reines and his co-workers present 3-pole RF MEMS tunable filters. In

their research paper, they used the suspended strip line combined with low loss

RF MEMS to increase the quality factor of the filter [40]. M.F. karim and co-

workers designed a tunable band stop filter by applying a capacitive change in

micromachined switches. These micromatchined switches were used as high

contrast capacitive elements between the coplanar waveguide ground plane and

all signal lines to tune the frequency. The tuning range achieved for this filter is

from 17.3 GHz to 19 GHz [41].

1.6.2 Varactor, Pin Diodes and Metamaterial Tunable Devices

For electrical tuning, He Lim and co-workers proposed tunable notch resonator

based on complementary split ring resonator (CSRRs) using varactor. They

called it varactor loaded complementary split ring resonator (VLCSRRs). They

designed this filter on a Taconic RF-35 substrate. This device was similar to the

SRR except for a varactor diode between internal and external resonators. In this

varactor, the resonant frequency was controlled by changing bias voltage.

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When there was no bias voltage on the varactor, it has large capacitance and low

resonance frequency. If the bias voltage increases, the capacitance of the

varactor become lesser , and the resonant frequency become higher. In the

VLCSRR outer conductor and inner conductor were connected, so chip

capacitors were added to both sides of the varactor for applying bias voltage, to

control the inductance of an outer ring of the counterpart. So by increasing the

bias voltage, capacitance of the varactor decreases, which means inductance of

the counterpart of the right side of outer slot gets smaller. Hence the resonant

frequency becomes higher or visa-versa [10].

Julio et al. also proposed a coplanar waveguide (CPW)-fed slot line ring

resonator which has been developed and integrated with varactor diodes to

create an electronically tunable planner resonator [11].

I. Gil. et al. demonstrated that the resonant frequency of split ring resonator

(SRRs) could be tuned using varactor diodes. The resulting particles, which was

called a varactor loaded split ring resonator (VLSRR) was applied to the design

of a tunable notch filter. The device consists on a microstrip transmission line

with VLSRRs placed at both sides of the conductor strip. Owing to the

proximity of the particles to the line, the rings were exited and a transmission

notch arises. It shows that by simply using two VLSRRs pairs, rejection levels

above 20db were achieved in 0.5 GHz tuning interval centred at 2.85 GHz [12].

Cumhur Cenk et al. proposed frequency tuning by placing on-off switches

between the rings of SRRs [13].

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Seung-Un Choi, proposed a hairpin tunable bandpass filter which enhanced

selectivity and tunability of circuits. The varactors loaded open stubs between

quarter-wavelength resonators were introduced to exhibit loss less transmission

near passband and thus better selectivity in the tuning range was achieved [24].

C.Lung Jr and J. Papapolymero designed a reconfigurable filter on Duroid

substrate. In this, they implement pin diodes as switching elements. They

designed the filter at 5.8 GHz and achieved passband tuning [42]. Adnam

Sondas and researchers also proposed a switchable antenna using pin diodes. In

this, they designed two loop elements and placed them asymmetrically at each

side of the twisted dipole, and placed pin diodes between the elements. They

achieved the switching from 3 GHz to 5.5 GHz [43]. J.X. Chen and his co

workers designed a uniplanar tunable and switchable bandpass filters, using the

centrally loaded slot line resonator. They used varactor as tuning element and

filter achieved 30.9 % frequency tuning, and for switching, they replaced the

varactors with the pin diodes [44].

1.6.3 Thin Film Tunable Devices

To overcome the contradiction between the microwave losses and the bias

voltage applied to the electrodes of planar transmission lines I.G.Mironenko has

proposed multi slot transmission lines (MSL) formed on (Ba.Sr)TiO3

ferroelectric films. They could realize high quality factor millimetre wavelength

devices, tuned by low bias voltages [2].

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Thin (Ba, Sr) TiO3 (BST) films have recently become the subject of extensive

research, since their dielectric nonlinearity makes it possible to fabricate

electronically tunable microwave devices. These electronically tunable

microwave devices include electronically scanned phased array antennas, low-

noise tunable heterodynes, tunable filters and parametric amplifiers.

Applications of thin-film analog phase shifters in adaptive duplexers of digital

vehicular communication systems enables one to reduce the noise level in

frequency bands of the receiving channels by 20 dB. Based on thin ferroelectric

films, multifunctional tunable devices have been fabricated in which a filter and

a phase shifter are integrated into a single microstrip circuit. In designing new-

generation beam formers, preference has recently been given to phase shifters

with ferroelectric varactors electrode which were made by planner technology.

In designing electronically tunable devices using ferroelectric films, the major

problem is associated with high insertion losses and control voltages. These

losses are usually minimized in two ways, by using a paraelectric ferroelectric

such as BaxSr1-x solid solutions and by improving the structural perfection of the

film [26].

Thin film exhibiting an electric-field tunable dielectric constant was investigated

for microwave frequency agile devices, such as phase shifters and filters. In

addition to a large tunability, these devices require dielectrics with low dielectric

losses. For the room temperature applications, thin film of ferroelectrics such as

(Ba,Sr)TiO3 (BST) have been extensively studied.

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Recently, thin films of nonferroelectric material, BZN, which has the cubic

pyrochore structure and a medium permittivity (170-200), has attracted interest

for tunable applications due to its very low losses and large tunabilitiy at low

frequencies. The tunability was defined as (εmax – εmin)/ εmax, where εmin was the

minimum measured permittivity at the maximum applied field, and εmax was the

dielectric constant at zero bias. J.Park and Co-workers designed Parallel plate

capacitors employing Bi1.5Zn1.0Nb1.5O7 (BZN) thin films with the pyrochlore

structure were fabricated on platinised sapphire substrates [21].

BZN ceramics exhibit a low temperature dielectric relation, i.e., a time lag

between the applied field and the polarization that was accompanied by a

dielectric loss peak. This loss peak shifts to higher temperature with higher

frequency, approaching room temperature in the microwave frequency region.

Therefore, bulk BZN is not suitable for applications requiring low losses in the

gigahertz (GHz) frequency regime. However, thin films may have different

properties. The tensile film stress, due to the thermal mismatch with a substrate,

reduce the activation energy of the dielectric relaxation and require higher

frequencies to shift the dielectric relaxation to higher temperature. Thus, BZN

films may remain attractive for low loss and high frequency applications.

A. Gensbittel and co-workers proposed that STO ferroelectric films associated

with high temperature superconductor is a good compromise to realize

electronically tunable microwave devices, combining with tunable dielectric

properties of FE films with low loss microwave conductivity in HTSC, STO,

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which exhibits a perovskite structure, is suitable for epitaxial growth of

YBaCuO films and has been widely studied to realize tunable components? STO

thin films were essentially deposited by sputtering and pulsed laser deposition.

In this work, they have explored the feasibility of microwave devices made from

STO thin films prepared by metalorganic chemical vapour deposition. They

characterized STO co-planar waveguide transmission lines and microwave

variable capacitors from 45 MHZ up to 40 GHz, in the 300 k to 60 k

temperature range [22]. Similarly, other researchers also worked on thin film

depositions for the tunable microwave devices, using different dielectric

substrates and the doping elements, which helps to reduce the losses and

increasing its performance abilities.

For magnetic tuning mainly, two approaches are followed-

1. Use of ferromagnetic thin films deposited on substrate to fabricate the

devices, for the better performance.

2. To make different resonators and cavity structures and attach ferrite rods

between these structures.

Lei Kang proposed that Left handed materials have some novel properties,

which never existed in natural materials, especially the sub wavelength

resolving power of electromagnetic waves. They used these materials for

designing and fabricating tunable devices. In this paper, SRR was fabricated in

which indium yttrium iron garnet (YIG) rod was attached into a periodic array

of split ring resonator. Different from those tuned by capacitance of equivalent

LC circuit, this metamaterial based approach used on mechanism of

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magnetically tuning inductance using the active ambient effective permeability

[4]. For magnetic tuning, researchers used ferrites or some ferroelectric

materials because these materials are magnetically tunable, and to improve the

performance they deposits thin films on these ferrite substrates [27].

A.A. Semsenov and co-workers fabricate YIG and BST films on the ferrite

substrate on which they made a resonator. This resonator has the dual tunability,

both electric tunability and magnetic tunability. It shows a broadband tunability

through the variation of the bias magnetic field, and narrow band tunability

through the variation of the bias electric field [15]. For dual BSTO, electrodes

made by the pulsed laser deposition of ferrite and ferroelectric layers and

sputtering the gold electrodes. This structure shows the dual tunability response

[14]. Erawan Salahun and many other researchers also deposited thin films

oxides and YIG and BST on the ferrite and silicon substrate to improve the

tunability response of the devices [19].

K.Aydin and E.Ozbay identified the magnetic response of SRR due to change in

its dielectric constant. In their experiment, they arranged the split ring resonator

in a periodic array between two magnetically charged poles [16]. Jerzy Krupka

and co-workers made a split ring resonator and attached ferrite rod between the

structures and placed this structure between poles of an electromagnetic. For

such structures the tuning speed of the order of milliseconds were achieved

using helical enclosure of the dielectric resonator instead of a metal cavity [3].

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M.F. Karim made a tunable bandstop filter by applying the capacitive change of

micromachined switches. The filter was realized by incorporating

electromagnetic bandgap structures with the micromachined switches. These

micromachined switches were used as high contrast capacitive elements

between the coplanar waveguide ground plane and the signal line, to tune the

frequency [17]. They also made a tunable bandstop filter using fractal

electromagnetic bandgap structure. The uniform structure was realized by

replacing the etched rectangular holes with the Minkowski loop generator. The

tunable bandstop filter was tuned by micromachined capacitive bridges. These

filters show low insertion loss and have a tuning range of 1.1GHz [17].

1.6.4 EBG Tunable Microwave Devices

Adnan Crour proposed a novel EBG structure for designing a tunable wide stop

band gap. In this two Microstrip open loop resonator were designed back to back

and it had only one unit cell inserted into microstrip line. The performance of

the device depends upon the width of the EBG structure [45]. Ceyhun Karpuz

successfully demonstrated wideband tuning capability using novel EBG circuit

with a single cell using a microstrip isosceles triangular patch inserted to the

microstrip line. Experimental and simulated results confirmed that the stopband

characteristics can be easily controlled by the slot dimension [46].

Zang Hui et. al. used liquid- crystals-filled photonic crystal waveguides. They

arranged the silicon rods in an array in a square lattice with the centre row rods

devoid so as to form waveguide. The remaining space was filled with nematic

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LC molecules. Then they applied the magnetic field and the device worked as

the magnetically tunable low-pass filter at terahertz frequency [8].

D. Kuytenstierna and his co-workers designed periodically loaded coplanar

waveguides (CPWs), and for tuning, they used ferroelectric varactors. They

achieved 20% tuning by applying 20V DC bias [47]. I. Gil and researchers also

designed a tunable resonator in CPW technology using EBG structures. In this

work, they loaded resonator with the shunt connected varactor diode and the

resulting structure can be electrically tuned from 1 to 2 GHz [48]. Bindu M.

Karyampudi and J.S Hong designed a compact coplanar waveguide defect

ground structure. They proposed some defect ground structures with and without

loading of lumped element capacitors. They also designed a varactor tuned

defected ground structure [49].

B.Jitha , P.C Bybi, C.K Anaandan and their co-workers proposed a microstrip

band reject filter using open loop resonator and they tuned these filters by

embedding varactor diodes in split [50]. Yongje Sung designed a tunable

bandstop filter using defect ground structure (DGS). To change the rejected

band of DGS section a moveable conducting plate was applied in parallel, over

an H-shaped defect on ground plane [51].

Wounjhang Park and Jeong-Bong Lee reported a tunable nanophotonic device

concept based on flexible photonic crystal, which comprised of a periodic array

of high-index dielectric material and a low index flexible polymer. Tunability

was achieved by applying mechanical force with nano/microelectochemical

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system actuators [52].

Z.L Deng, N.B Zhang and J.M Huang designed an ultra wideband bandstop

filter, tuned by MEMS based switches, based on EBG and CPW structures. The

centre frequency of stop band was changed from 5 to 15 GHz by tuning the

MEMS switch [53]. M.F Karim and co-workers designed a reconfigurable filter

using EBG structure which can be switched from bandpass to bandstop filter at

some frequency by pin diodes [54]. M.F Karim also designed a MEMS based

tunable bandstop filter using EBG structures. In this, he etched square slots at

the backplane of the CPW transmission lines and achieved tunability from 19

GHz to 17.3 GHz [55].

Ping Chen and researchers studied the transmission properties of two

dimensional (2D) ferrite EBG materials under a static applied magnetic field. In

this, they fabricated ferrite rods and arranged them in a hexagonal lattice and

inserted them into a Plexiglas substrate and then by applying magnetic field they

achieved the tuning in S21 parameters [56]. Susanta Kumar and Santanu Das

proposed a U-headed dumb bell defected ground structure, which combines two

shaped slots by a thin transverse rectangular slot. Two cells of the above DGS

under microstrip line show low pass as well as bandstop characteristics and its

stop band can be tuned by varying the distance between the slot- arms of the U-

shaped aperture and transverse slot width [57].

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A tunable band stop filter using fractal electromagnetic band gap structure was

designed. The uniform fractal EBG structure was realized by replacing the

etched rectangular holes with Minkowski loop-generator. This tunable filter was

tuned by micro machined capacitive bridge [58]. Chul Sik Kee and H.Lim

showed that the two dimensional photonic crystals constructed with the square

rods of intrinsic semiconductor in the air which can exhibit a complete band gap

common to S and P polarized waves in THz range. This is a complete bandgap

which is easily tunable by using temperature dependence of plasma frequency of

intrinsic semiconductors [59].

1.7 Steps follow in Thesis

Objective of the present work were achieved through well planed methodology

in following steps:

1.7.1 Problem Definition

The aforemost task of any research work in a given field is identification of a

direction. A logically feasibly, physically realizable and commercially

applicable problem statement often result in path breaking technologies.

Keeping in view the foresaid point it was proposed to directionalize this research

work towards, “DESIGN, FABRICATION AND ANALYSIS OF TUNABLE

PLANAR MICROWAVE DEVICES USING EBG STRUCTURES.”

Chapter1

1.7.2 Literature Review

To know the state of the art in the chosen direction intensive literature analysis

was carried out to equip with the latest research trends, advantages &

disadvantages of the methods and the pressing need from consumer market. This

step laid foundation to move over to the next level of design and simulation.

1.7.3 Simulation & Theoretical Modelling

The Microwave Lab at Department of Physics & comp. Science in the

Dayalbagh Educational Institute is well equipped with the best simulation

environment like Microwave Studio Suite & RF Band solve, to simulate

logically feasible idea for its physical realization.

To achieve the objective various 2-Dimentional EBG lattice were simulated and

finally honeycomb lattice and triangular lattice with hexagonal basis points

were considered for final design due to following reasons:

Hexagonal basis points can accommodate maximum number of

neighbours.

Lattice results in closed packed structure.

Flexibility to create different defect.

1.7.4 Methods of Tunability

Microwave devices can be tuned mechanically by using a spacer or

electromagnetically by using suitable active components or using thin films of

ferrite.

Chapter1

In the present work both ways of tuning viz mechanical & electromagnetic were

considered. To achieve electromagnetic tuning thin film of nano structured

ferrite material was proposed to be used by conventional spin coating method.

Nano powder of Fe2O3 was purchased from Sigma Aldrich. Nano solution was

prepared by sol gel methods and thin films were deposited on RT-Duroid using

spin coating method. But the main challenge was dielectric characterization of

nano samples. As mostly, available methods focus on either liquid

characterization [11] or thin film or pallet characterization [12].

1.7.4 Dielectric Characterization

To carryout dielectric characterization, a detailed study was taken up & planar

concentric ring resonator was simulated. A detailed theoretical modelling was

done for the designed devices. Concentric split and closed ring resonator were

fabricated on FR-4 substrate and various materials in varying forms ferrite-

biomaterial were characterized for validating the method [13].

1.7.5 Fabrication

Fabrication of 2-dimensional metallic EBG lattice on RT-duroid was carried out

by conventional photolithography method. The EBG lattice structures were

designed at 17 GHz and the bandgap properties were extracted from the RF

bandsolve simulation package. Microwave signal was fed in EBG lattice

through a microstripline. A suitable rectangular aluminium housing was

designed with appropriate consideration for feed.

Chapter1

1.7.6 Experimentation

The microwave lab in Department of Physics and computer Science has in-

house measurement facility with 50 GHz Rhode & Schwarz Network Analyzer.

Repeated experiments were carried out for analyzing the behaviour of designed

structures and its tunability. Transmission coefficient showed wide bandstop

region from 32 GHz to 41 GHz and 1.25 GHz tuning was also observed by

mechanical method. Electromagnetic tuning is also reported in the last chapter.

1.8 Research Outcome

This proposed doctoral work has lead to the development of the novel tunable

microwave devices having low losses and electromagnetic tunability from EBGs.

As planar EBG fabrication is compatible to the conventional MIC (Microwave

integrated Circuits) fabrication technology, it is proposed that these devices will

find greater applicability in steerable systems due to their very low radiation and

thermal noises.

Chapter1

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