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Session: 2010-11

MORADABAD INSTITUTE OF TECHNOLOGY

MORADABAD

CERTIFICATE

This is to certify that the seminar entitled “ Compact Microstrip Bandstop Filter Covering S-Band to

Ku-Band” submitted by Rajesh Kumar Roll No. 0808231072 in partial fulfillment of the requirement

of the Degree of B.Tech. in Electronics & Communication Engineering embodies the work done by

him under my guidance.

Signature of the Seminar Guide Signature of the Seminar Coordinator

Ms. Alpana Singh Mr. Farooq Husain

Assistant Professor Associate Professor

Date---------- Date----------

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MORADABAD INSTITUTE OF TECHNOLOGY, MORADABAD

Department of Electronics & Communication Engineering

Compact Microstrip Bandstop Filter

Covering S-Band to Ku-Band

Name of Student: Rajesh Kumar Roll No.:

Guide: Ms. Alpana Singh Semester: 6th

Session: 2010-11

Branch: Electronics & Communication Engg.

________________________________________________________________

Synopsis: This topic reports a wide bandwidth planar bandstop filter with improved RF

characteristics. The proposed filter on alumina is realized incorporating tapped open stub along with

spurline topology. Further, stepped impedance resonator (SIR) approach has been introduced in the

tapped stubs to achieve wider band performance with improved selectivity. The proposed topology

effectively controls the transmission poles. Fabrication of this BSF has been carried out on glass

substrate showing minimal effect of permittivity variation on bandwidth performance. This validates

the applied approach with achievable bandwidth of more than 100% ranging from S- to Ku-band.

Close agreement with simulation and practical results have been demonstrated with measured

insertion loss of less than 1 dB and attenuation loss better than 30 dB at C-band.

Signature of Student Signature of Seminar guide

Signature of Seminar Coordinator Signature of H.O.D

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ACKNOWLEDGEMENT

I express my deepest sense of gratitude towards my guide Ms. Alpana Singh (Asst. Professor),

Department of Electronics & Communication Engineering, Moradabad Institute of Technology,

Moradabad for her patience, inspiration, guidance, constant encouragement, moral support, keen

interest, and valuable suggestions during preparation of this seminar report.

My heartfelt gratitude goes to all faculty members of Electronics & Communication

Engineering Deptt., who with their encouraging and caring words and most valuable suggestions

have contributed, directly or indirectly, in a significant way towards completion of this seminar

report.

I am indebted to all my classmates for taking interest in discussing my problem and encouraging

me.

I owe a debt of gratitude to my father and mother for their consistent support, sacrifice, candid

views, and meaningful suggestion given to me at different stages of this work.

Last but not the least I am thankful to the Almighty who gave me the strength and health for

completing my report.

Rajesh Kumar

Roll No.

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LIST OF ABBREVIATION

DBR DUAL BEHAVIOR RESONATOR

SIR STEPPED IMPEDANCE RESONATORS

PBG PHOTONIC BAND GAP

EBG ELECTRONIC BAND GAP

DGP EFFECTED GROUND PLANE

UIR UNIFORM IMPEDANCE RESONATOR

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LIST OF SYMBOLS

Z1 Characteristic impedance of transmission line 1

Z2 Characteristic impedance of transmission line 2

Zin Resultant impedance of transmission lines when

cascaded

Θ1 Electrical length of transmission line 1

Θ2 Electrical length of transmission line 2

R Impedance ratio of SIR

Ɛr Relative permittivity

μ Refractive index

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LIST OF FIGURES

FIGURE No. CAPTION PAGE No.

1.1 FREQUENCY SPECTRUM 2

1.2 FREQUENCY BAND DESIGNATION 3

1.3 CROSS SECTIONAL DESIGN OF MICROSRTRIP LINES 3

1.4 MICROSTRIP SPURLINE NOTCH FILTER 6

1.5 OUTPUT OF BAND STOP FILTER 7

2.1 PROPOSED WIDEBAND BSF 8

2.2 BASIC STRUCTURE OF THE OPEN-ENDED SIR 9

3.1 COMPARISON OF THE PROPOSED TOPOLOGY WITH

SPURLINE

10

3.2 COMPARISON OF THE SIR STUBS WITH THE UIR

STUBS

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3.3

EFFECT OF THE SUBSTRATE PERMITTIVITY ON THE

RF CHARACTERISTICS OF BSF

12

5.1 LAYOUT OF BSF ON ALUMINA 14

5.2 SIMULATED AND MEASURED RESULT 15

5.3 MEASURED VERSES SIMULATED RESULT ON GLASS

SUBSTRATE

16

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TABLE OF CONTENTS

CONTENT PAGE No.

CERTIFICATE ii

SYNOPSIS iii

ACKNOWLEDGEMENT iv

LIST OF ABBREVIATIONS v

LIST OF SYMBOLS vi

LIST OF FIGURES vii

CHAPTER 1 INTRODUCTION 1

1.1 FREQUENCY SPECTRUM 2

1.2 MICROSTRIP LINES 3

1.3 Ku BAND 4

1.4 S BAND 5

1.5 SPURLINE 6

1.6 BAND STOP FILTER

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CHAPTER 2 DESIGN METHODOLOGY 8-9

2.1 SIR APPROACH

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CHAPTER 3 PARAMETRIC STUDY 10-11

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3.1 BANDWIDTH COMPARISON 10

3.2 EFFECT OF UNIFORM IMPEDANCE

RESONATOR (UIR)

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3.3 PERMITTIVITY VARIATION

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CHAPTER 4 FILTER FABRICATION

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CHAPTER 5 MEASUREMENT RESULTS

13-17

CHAPTER 6 ADVANTAGES

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CHAPTER 7 APPLICATIONS

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CHAPTER 8 CONCLUSION

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REFRENCES

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LIST OF PUBLICATIONS 21

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CHAPTER 1

INTRODUCTION

Band stop filters find applications in oscillator and mixers to remove higher-order

harmonics and other unwanted spurious signals. Duplexers and switches are comprised of

BSF for filtering out unwanted signal along as they can interfere with the desired signals.

Conventional methods to implement bandstop filters involve use of shunt stubs or stepped-

impedance microstrip lines with large circuit size. To reduce filter area, certain slow-wave

structures, such as open-loop resonators, are widely adopted. These traditional BSFs are

normally having the narrow stop band response. As demand for wider stop band is gaining

popularity alternative structures like photonic band gap (PBG) electronic band gap (EBG),

and the defected ground plane (DGS) are explored to cater the demand. Further to enhance

the stop bandwidth, use of four or more cells of above-mentioned topologies is needed.

However, this leads to a larger size and more transmission losses in the stop band.

Alternatively, EBG and DGS require etching process on the backside ground plane in

addition to position calibration using costlier lithographic techniques. Further its turnaround

time is high and makes it incompatible to match with other topologies in the overall system

configuration. Proposed spurline with cross-junction open stubs to have wider bandwidth

with small size, but selectivity at one frequency end is compromised to cater for wider

bandwidth. All the reported circuits are restricted to lower end of frequency where the effects

of losses are not prominent, making it easier to analyze. Wider bandwidth topology at higher

frequencies covers 2.3GHz to 9.5GHz range but has limited bandwidth. Spurline with SIR

approach but concentrated mainly on selectivity aspect rather than bandwidth enhancement.

This report demonstrates for the first time, a simple spurline topology with tapped

stepped impedance resonators- (SIR-) based open stubs. These stubs can be construed as a

dual-behavior resonator (DBR), controlling the selectivity with placement of the attenuation

zeros at the desired frequencies. Various simulation studies are carried out to study the effect

of substrate permittivity, uniform impedance resonator, and so forth, on the performance of

the proposed filter. Presented approach is validated with practical data by realization of this

filter on both alumina and on glass substrate.

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1.1 FREQUENCY SPECTRUM

Figure below depicts the electromagnetic radiation spectrum and some of the commonly

used or known areas.

FIGURE 1.1. ELECTROMAGNETIC RADIATION SPECTRUM

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Figure 1.2 shows the areas of the spectrum which are frequently referred to by band

designations rather than by frequency.

FIGURE 1.2 FREQUENCY BAND DESIGNATIONS

1.2 MICROSTRIP LINES

FIGURE 1.3 CROSS SECTIONAL DESIGN OF MICROSTRIP LINES

Cross-section of microstrip geometry. Conductor (A) is separated from ground plane (D) by

dielectric substrate (C). Upper dielectric (B) is typically air.

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Microstrip is a type of electrical transmission line which can be fabricated using printed

circuit board [PCB] technology, and is used to convey microwave-frequency signals. It

consists of a conducting strip separated from a ground plane by a dielectric layer known as

the substrate. Microwave components such as antennas, couplers, filters, power dividers etc.

can be formed from microstrip, the entire device existing as the pattern of metallization on

the substrate. Microstrip is thus much less expensive than traditional waveguide technology,

as well as being far lighter and more compact.

The disadvantages of microstrip compared with waveguide are the generally lower power

handling capacity, and higher losses. Also, unlike waveguide, microstrip is not enclosed, and

is therefore susceptible to cross-talk and unintentional radiation.

For lowest cost, microstrip devices may be built on an ordinary FR-4 (standard PCB)

substrate. However it is often found that the dielectric losses in FR4 are too high at

microwave frequencies, and that the dielectric constant is not sufficiently tightly controlled.

For these reasons, an alumina substrate is commonly used.

On a smaller scale, microstrip transmission lines are also built into monolithic microwave

integrated circuits [MMIC]s.

Microstrip lines are also used in high-speed digital PCB designs, where signals need to be

routed from one part of the assembly to another with minimal distortion, and avoiding high

cross-talk and radiation.

Microstrip is very similar to stripline and coplanar waveguide [CPW], and it is possible to

integrate all three on the same substrate.

1.3 Ku BAND

The Ku band is a portion of the electromagnetic spectrum in the microwave range of

frequencies. This symbol refers to "K-under" (originally German: Kurz-unten)—in other

words, the band directly below the K-band. In radar applications, it ranges from 10.95-

14.5 GHz according to the formal definition of radar frequency band nomenclature in IEEE

Standard 521-2002.

Ku band is primarily used for satellite communications, most notably for fixed and broadcast

services, and for specific applications such as NASA's Tracking Data Relay Satellite used for

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both space shuttle and ISS communications. Ku band satellites are also used

for backhauls and particularly for satellite from remote locations back to

a television network's studio for editing and broadcasting. The band is split into multiple

segments that vary by geographical region by the International Telecommunication

Union (ITU). NBC was the first television network to uplink a majority of its affiliate feeds

via Ku band in 1983

Some frequencies in this radio band are used for vehicle speed detection by law enforcement,

especially in Europe

Ku band is not similarly restricted in power to avoid interference with terrestrial microwave

systems, and the power of its uplinks and downlinks can be increased. This higher power also

translates into smaller receiving dishes and points out a generalization between a satellite’s

transmission and a dish’s size. As the power increases, the dish’s size can decrease.[4]

This is

because the purpose of the dish element of the antenna is to collect the incident waves over

an area and focus them all onto the antenna's actual receiving element, mounted in front of

the dish (and pointed back towards its face); if the waves are more intense, less of them need

to be collected to achieve the same intensity at the receiving element.

The Ku band also offers a user more flexibility. A smaller dish size and a Ku band system’s

freedom from terrestrial operations simplifies finding a suitable dish site. For the End users

Ku band is generally cheaper and enables smaller antennas (both because of the higher

frequency and a more focused beam).[5]

Ku band is also less vulnerable to rain fade than the

Ka band frequency spectrum.

The satellite operator's Earth Station antenna do require more accurate position control when

operating at Ku band than compared to C band. Position feedback accuracies are higher and

the antenna may require a closed loop control system to maintain position under wind loading

of the dish surface.

1.4 S BAND

The S band is defined by an IEEE standard for radio waves with frequencies that range from

2 to 4 GHz, crossing the conventional boundary between UHF and SHF at 3.0 GHz. It is part

of the microwave band of the electromagnetic spectrum. The S band is used by weather radar,

surface ship radar, and some communications satellites, especially those used by NASA to

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communicate with the Space Shuttle and the International Space Station. The 10-

cm radar short-band ranges roughly from 1.55 to 5.2 GHz

In some countries, S band is used for Direct-to-Home satellite television (unlike similar

services in most countries, which use Ku band). The frequency typically allocated for this

service is 2.5 to 2.7 GHz (LOF 1.570 GHz).

Wireless network equipment compatible with IEEE 802.11b and 802.11g standards use the

2.4 GHz section of the S band. Digital cordless telephones operate in this band

too. Microwave ovens operate at 2495 or 2450 MHz. IEEE 802.16a and 802.16e standards

utilize a part of the frequency range of S band, under WiMAX standards most vendors are

now manufacturing equipment in the range of 3.5 GHz. The exact frequency range allocated

for this type of use varies between countries

1.5 SPURLINE

The spurline is a type of radio-frequency and microwave distributed element filter with band-

stop (notch) characteristics, most commonly used with microstrip transmission lines.

Spurlines usually exhibit moderate to narrow-band rejection, at about 10% around the central

frequency.

Spurline filters are very convenient for dense integrated circuits because of their inherently

compact design and ease of integration: they occupy surface that corresponds only to a

quarter-wave length transmission line.

STRUCTURE DESCRIPTION

It consists of a normal microstrip line breaking into a pair of smaller coupled lines that rejoin

after a quarter-wavelength distance. Only one of the input ports of the coupled lines is

connected to the feed microstrip, as shown in the figure below. The orange area of the

illustration is the microstrip transmission line conductor and the gray color the exposed

dielectric.

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FIGURE 1.4: MICROSTRIP SPURLINE NOTCH FILTER (TOP VIEW)

Where λg is the wavelength corresponding to the central rejection frequency of the bandstop

filter, measured - of course - in the microstrip line material. This is the most important

parameter of the filter that sets the rejection band.

The distance between the two coupled lines can be selected appropriately to fine-tune the

filter. The smaller the distance, the narrower the stop-band in terms of rejection. Of course

that is limited by the circuit-board printing resolution, and it is usually considered at about

10% of the input microstrip width.

The gap between the input microstrip line and the one open-circuited line of the coupler has a

negligible effect on the frequency response of the filter. Therefore it is considered

approximately equal to the distance of the two coupled lines

1.6 BAND STOP FILTER

In signal processing, a band-stop filter or band-rejection filter is a filter that passes

most frequencies unaltered, but attenuates those in a specific range to very low levels. It is the

opposite of a band-pass filter. A notch filter is a band-stop filter with

anarrow stopband (high Q factor). Notch filters are used in live sound reproduction (Public

Address systems, also known as PA systems) and in instrument amplifier(especially

amplifiers or preamplifiers for acoustic instruments such as acoustic guitar, mandolin, bass

instrument amplifier, etc.) to reduce or prevent feedback, while having little noticeable effect

on the rest of the frequency spectrum. Other names include 'band limit filter', 'T-notch filter',

'band-elimination filter', and 'band-reject filter'.

Typically, the width of the stopband is less than 1 to 2 decades (that is, the highest frequency

attenuated is less than 10 to 100 times the lowest frequency attenuated). In the audio band, a

notch filter uses high and low frequencies that may be only semitones apart.

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FIGURE 1.5 OUTPUT OF BANDSTOP FILTER

CHAPTER 2

DESIGN METHODOLOGY

A standard spurline filter design using theoretical equations and CAD tool has been

carried out. The stubs are incorporated at the input and output ports for enhancing RF

performance. Impedances of the stubs are chosen so that overall ratio of impedances is not

altered in tapped stubs. Effect of different impedance ratios is studied and bandwidth can be

enhanced by varying this ratios. Symmetry of the structure is maintained and compactness is

achieved by folding the stubs (Figure 2.1).

FIGURE 2.1 PROPOSED WIDEBAND BSF

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Still, the selectivity improvement needs optimization which was achieved by using the

coupled effects between the non-uniform lengths as shown in Figure 2.1 (marked A).

2.1. SIR APPROACH

FIGURE 2.2 BASIC STRUCTURE OF THE OPEN-ENDED SIR

The impedance of the SIR resonator shown in Figure 2.2 can be derived using the

transmission line theory, as follows:

where Z1 and Z2 are the characteristics impedances of the two cascaded sections, θ1

and θ2 are the corresponding electrical lengths (θ1 + θ2 = π). For determining the resonance

frequency of the SIR, using (1) with Zin = 0 yields

tan θ1 = R cot θ2 (2)

where R is the impedance ratio of the SIR defined as

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The resonance condition of the SIR can be adjusted by changing the width and length

of Z1 and Z2. Frequency tuning is facilitated by adjusting R, as poles and zeros position

directly depend on R. In the present design, three different impedances are simultaneously

tuned to achieve wider band performance.

CHAPTER 3

PARAMETRIC STUDY

Electromagnetic simulation study has been carried out by varying parameters like

permittivity and impedances of the stubs . All these studies have been carried out on 10 mils

alumina substrate to cater high frequency of operation.

3.1. BANDWIDTH COMPARISON

Proposed BSF topology has been compared with standard spurline topology and it

shows more than three times improvement in bandwidth. This is attributed due to the five

transmission poles resulting in wider stop band attenuation as shown in Figure 3.1

FIGURE 3.1 COMPARISON OF THE PROPOSED TOPOLOGY WITH SPURLINE

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3.2. EFFECT OF UNIFORM IMPEDANCE RESONATOR (UIR)

Tapped open stubs based on SIR approach have been replaced with UIR stubs as

shown in Figure 3.2 keeping intact the overall dimensions and widths. UIR approach

degrades the performance in terms of attenuation and selectivity as poles placement at the

desired location cannot be controlled without optimization and keeping overall dimensions

intact.

FIGURE 3.2 COMPARISON OF THE SIR STUBS WITH THE UIR STUBS

3.3. PERMITTIVITY VARIATION

Due to inherent broadband nature of the proposed structure, variation of RF

characteristics due to variable substrate permittivity has also been carried out. Structural

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dimensions optimized on alumina have been replicated on silicon and glass without

dimensional changes and resulting EM simulation shows minimal influence of permittivity

on the bandwidth. As shown in Figure 5, Si ( εr = 11.8) permittivity is close to Alumina ( εr

= 9.98), so performance is least affected and further drastically changing the permittivity to

4.82 (Glass), the shift in frequency is observed without affecting the inherent broadband

characteristics.

FIGURE 3.3 EFFECT OF THE SUBSTRATE PERMITTIVITY ON THE RF

CHARACTERISTICS OF BSF

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CHAPTER 4

FILTER FABRICATION

The band stop filter discussed is fabricated on the Pyrex 7740 glass substrate having

thickness of 550 μ and on 10 mil alumina substrate. The fabrication on alumina uses standard

lithography processing steps but on glass substrate an extra step of thin film metallization is

carried out. After subjecting to standard thin film substrate cleaning cycles, glass substrates

are sputtered with thin layer of Cr (200– 300 ° A) followed by 7000 °A of gold film on both

sides of

Substrates. The sputtered metallization is electroplated with gold to the required thickness of

4.5 μ± 3% and circuits are patterned using standard optical lithography and subtractive

etching process. The patterned substrate (both Al/Glass) is attached to gold metallized Kovar

carrier plate using silver-based conductive epoxy. The carrier plate is mounted on test jig and

RF connectors are connected by gold ribbon of 20 mils width and 1mil thickness using

parallel gap welding.

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CHAPTER 5

MEASUREMENT RESULTS

Extensive CAD optimization has been carried out to achieve the desired

specifications of broadband width. Filters realized on the alumina and glass substrate are

tested using the vector network analyzer PNA (8261A) from Agilent Technologies. Layout of

the fabricated filter on alumina substrate is shown in Figure 5.1.

FIGURE 5.1 LAYOUT OF BSF ON ALUMINA

The overall size comes around 7.5mm × 4.05mm Comparison of simulated and measured

results shows close agreement as shown in Figure 5.2 .

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FIGURE 5.2 SIMULATED AND MEASURED RESULT

Figure 5.3 depicts measured performance on the glass substrate patterned using

same mask. It shows a very wide band performance indicating minimal effect of substrate

permittivity on bandwidth. Higher losses in the bandstop structure are associated with the

increase of dielectric losses associated with glass tan δ which needs parameters optimization.

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FIGURE 5.3 MEASURED VERSES SIMULATED RESULT ON GLASS SUBSTRATE

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CHAPTER 6

ADVANTAGES

Advantages of ultra wide bandwidth

High attenuation

Smooth pass band

Compact size

Easy fabrication process.

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CHAPTER 8

APPLICATIONS

Used in oscillators and mixers to remove higher-order harmonics and other unwanted

spurious signals.

Used to suppress harmonics in microwave integrated circuit and THz applications.

Applied to circuit applications requiring broadband-filtering function.

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CHAPTER 9

CONCLUSION

Band stop filter with a wide bandwidth is proposed in this paper keeping intact the

length as of standard spurline topology. The filter consists of one spurline and a pair of SIR

stubs to achieve more than 100% bandwidth. Measured and simulated results are shown to be

in close agreement. Proposed filter demonstrates better bandstop characteristics compared to

existing reported structures retaining the compactness. Unique feature in the proposed

topology is wide tolerance level for the substrate permittivity variation demonstrated by

measurement and comparing its performances practically using both alumina and glass

substrate. The proposed topology can also be easily implementable in MMIC.

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REFERENCES

[1] http://www.hindawi.com/journals/ijmst/2010/624846.html

[2] http://www. ieeexplore.ieee.org/iel5/7260/31399/01458813.pdf

[3] http://www.ntu.edu.sg/home/eyhlee/Prof%20Lee/2005%20MOTL.pdf

[4] http://www.cst-china.cn/pdf/application/MicrostripBandstopAndLowpassFilters.pdf

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LIST OF PUBLICATIONS

[1] J. S. Hong and M. J. Lancaster, Microstrip Filters for RF/Microwave Applications, John

Wiley & Sons, New York, NY, USA, 2001.

[2] J. Shi, J. X. Chen, and Q. Xue, ―Compact microstrip lowpass filter with wide stop-band

integrating a bandstop structure in an open-loop resonator,‖ Microwave and Optical

Technology

Letters, vol. 47, no. 6, pp. 582–584, 2005.

[3] H. W. Liu, Z. Shi, R. H. Knoechel, and K. F. Schuenemann, ―Circuit modeling of spurline

and its applications to microstrip bandstop filters,‖ Microwave Journal, vol. 50, no. 11, pp.

126–

130, 2007.

[4] M. Y. Hsieh and S. M. Wang, ―Compact and wideband microstrip bandstop filter,‖ IEEE

Microwave and Wireless Components Letters, vol. 15, no. 7, pp. 472–474, 2005.

[5] Y. Z. Wang and M. L. Her, ―Compact microstrip bandstop filters using stepped-

impedance resonator (SIR) and spurline sections,‖ IEE Proceedings: Microwaves, Antennas

and

Propagation, vol. 153, no. 5, pp. 435–440, 2006.

[6] E. Rius, C. Quendo, C. Person, A. Carlier, J. Cayrou, and J. L. Cazaux, ―High rejection C-

band planar band-pass filter for a spatial application,‖ in Proceedings of the 33rd European

Microwave Conference, pp. 1055–1058, Paris, France, October 2005.

[7] ―AC microwave, Linmic 6.2 +/N user manual‖.