compact micro strip band stop filter
TRANSCRIPT
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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
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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
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5.1 LAYOUT OF BSF ON ALUMINA 14
5.2 SIMULATED AND MEASURED RESULT 15
5.3 MEASURED VERSES SIMULATED RESULT ON GLASS
SUBSTRATE
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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‖.