International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 5- March 2016
Design of Novel Tri-Band Bandpass Sri
Structure Microstrip Filter
M.Amudhan#1, S.Annin renisha*2, P.Padmavathi#3, S.Parani*4, M.Vaidegi#5
Department of Electronics and Communication Engineering
Achariya College of Engineering and Technology
Abstract— In this paper, a microstrip structure is
designed to realize a tri-band band pass filter. The
proposed band pass structure uses a microstrip
resonator with three independently controlled
resonance frequencies producing three frequency
bands of interest controlled by adjusting the
dimensions of the resonator. Parametric analysis is
performed on the structure to determine the optimum
dimensions to obtain the desired frequency response
and is explained in the paper. The tri-band band
pass filter developed in this paper exhibits tri
operating frequencies at 2.4GHz, 5GHz and 5.8GHz
with 0.51GHz, 1.70GHz and 0.41GHz bandwidths
for each band respectively. We achieved a compact
tri-band band pass filter with controllable resonance
frequencies and insertion losses in the pass band
with high selectivity. The measured results are in
good agreement with simulated results.
Keyword— Insertion loss, return loss, resonator,
band.
I
INTRODUCTION
Recently, extensive research efforts have
focused on
realization of compact microwave
structures for multiband wireless services and tri
communication channels to reduce the circuit
size and cost of the communication equipment
such as dual-band and tri-band waveguide guide
filter [1, 2], dual-band filter in ring [3] and dualband filters [4,5, 6]. In this paper, a dual band
bandpass filter structure is investigated which is
compact in size and can be easily integrated. In
general, conventional tri-band filters are designed by
cascading two filter structures with different pass
band. But tri-band filters realized using this
approach required three different filters and the size
of these tri-band filters is comparatively large.
Therefore, a single circuit with tri-band response is
preferred to reduce circuit area and thereby cost.
Many approaches have been previously presented
for realization of integrated dual-band filters. For
Example, in [7] and [8] dual-band and tri band filters
are designed using stub loaded resonator and ring
resonator by utilizing the tri-band characteristics of
SIRs. One of the advantages of designing tri-band
filters using SIRs is that the position of the tri-bands
can be designed conveniently. However, it is
difficult to adjust the coupling between the
ISSN: 2231-5381
resonators to meet tri-band specifications of the filter
simultaneously [10]. For the tri-band filter designed
using stubs loaded resonator in [7], the maximal
|S11| magnitudes over the pass bands are about 10
dB and a tri-band impedance transformer has to be
used in order to improve the performance. Thus,
with the design method specified in [7], inclusion of
an impedance transformer to improve the return loss
(|S11|) makes the circuit area larger. In [11], a
fourth-order tri-band band pass filter has been
developed with equal-length SIR resonators with
three-high impedance transformers placed between
the input 50 ohm lines and the SIRs to achieve better
frequency response characteristics. The main
advantages of filters we present in this paper include
the realization of a more compact structure operating
at dual frequencies that can be controlled
independently, with low insertion loss (|S21| <=1.2
dB) and high return loss (|S11>= 15 dB) in both
pass bands, and without the need for impedance
transformation.
The structure discussed in this paper is a
modification of the conventional step impedance
resonators (SIRs) proposed. The resonators used in
this filter are used to shift high frequency by
combing the microstrip. The main advantage in using
SIRs is controlling the frequency response and
insertion loss possibilities and identical values of the
characteristic impedances. This novel compact
structure has not been designed or discussed
previously in realization of microwave filter
structures. Extensive parametric analysis was
performed to understand the effect of the various
parameters on filter performance. All the simulations
presented in this paper are done using HFSS software
Ansoft Designer. Simulations results were verified
experimentally. This paper is organized as follows.
In Section 2, the design of the proposed dual-band
band pass filter is discussed. Section 3 represents the
simulation and results of the designed filter structure
which determine the optimum dimensions of the
structure to achieve a practical filter with improved
pass bandwidths and selectivity.
II DESIGNING OF FILTER MODEL
The filters are designed and simulated by using
HFSS software Ansoft designer the designed filter
consists of FR4 dielectric substrate(Er) with the
value 4.4 and its height h is 1.6. At the bottom of
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 5- March 2016
substrate contains a copper ground plane with
thickness of about 0.035. The conducting strip is
designed above the substrate with height 1.6 and
thickness 0.035. The Fig 1 shows filter model
Fig 2 Physical layout of SRI Structure Filter
C. Details of the Resonators
The SRI structure is obtained by coupling
different resonator into single structure. The
dimensions of each resonator are shown in table I.
III
TABLE I
DIMENSION OF SRI STRUCTURE
Fig 1 Filter model
Dimension
Values(mm)
L1
8
L2
8.8
L3
16
L4
9.5
L5
6.8
L6
2.2
L7
1.7
L8
3
L9
3.5
L10
10.8
L11
21
L12
3.2
L13
5.6
W
2.8
A. Design and analysis of Tri-Band
SRI
Structure Filter
The designed microstrip technology realizes tri
band bandpass characteristics in comparison to the
conventional step-impedance resonator. In order to
exhibit tri- band pass characteristic, the lengths of
the new structure are chosen such that they resonate
at the three desired frequencies (say f1,f2 and f3). The
resonance frequency (f1 or f2 or f3) depends on the
length of each resonator, dielectric constant of the
substrate, its thickness, and trace width. Since the
resonators are frequency selective, the conventional
step impedance resonators are excited only when the
signal frequency is close to the resonant frequency.
At signal frequencies close to f1, the resonators get
excited and the signal propagates from the input port
to the output port, when frequencies close to f2 the
resonators propagates the signal between both the
frequency f1 and f2, for the signal is very close f3 the
signal gets propagated to the output port.
B. Designed SRI Structure Layout
The SRI structure is designed and simulated by
using the HFSS software Ansoft designer. The total
dimension of the structure is 25*25*1.6.The gaps
between the resonator and the thickness of the
feedlines is 0.035. To obtain the output response the
SRI structure are allow to propagate at 1GHz. The
Fig 1 gives the physical structure of the SRI filter.
ISSN: 2231-5381
IV
RESULTS AND SIMULATIONS
This section describes the effect of various
parameters on the frequency of resonance and how
optimum dimensions for the structure are determined.
The parameters that control the frequency response
characteristics of the structure are labelled in Figure
3. Initially, the length of the resonator (L1) is 5 mm,
width of the resonator arms (w) is equal to 2.8mm,
the coupling space (s) between the adjacent
resonators is chosen is to be 5mm, input and output
feed lines are directly tapped on to the resonators
without any offset and the dimensions of the other
parameters are L1=8mm,L2=8.8 mm, L3=16mm,L4
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International Journal of Engineering Trends and Technology (IJETT) – Volume 33 Number 5- March 2016
= 9.5mm, L5=6.8mm, L6=2.2mm, L7=1.7mm,
L8=3mm,L9=3.5mm,L10=10.8mm,L11=21mm,L12
=3.2mm, L13=5.6mm and W= 2.8mm.
A. Return loss (s11)
It means how much power is reflected. For
instance, a return loss of 3db means half the power is
reflected and a return loss of 20db means 1% of the
power is reflected. The value of the return loss will
always be in negative. It can be calculated by using
the following formula
Return Loss = 20log (Incident power / Reflected
power).
The return loss of the filter is shown in the Fig
3. The obtained losses are -16.9dB, -11.2dB and 16.7dB at frequency 2.4GHz, 5GHz and 5.8GHz
respectively.
parameters of the structure on the frequency
response characteristics of the structure were
investigated using parametric analysis in commercial
HFSS software. A filter prototype was fabricated
using the optimized dimensions obtained. A milling
machine used to fabricate the prototype filter.
Experimental
measurements
and
theoretical
simulations of the filter showed excellent return loss
and insertion loss in both frequency bands.
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Fig 3 Simulated S11 response of the filter
A. Insertion loss (s21)
The insertion loss of a line or network is defined
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V
CONCLUSIONS
A new compact tri-band band pass filter has
been successfully realized with measured tri
operating frequencies at 2.4GHz, 5GHz and 5.8GHz
with insertion losses less than -5dB and return losses
greater than -10dB. The influence of the geometric
ISSN: 2231-5381
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