INTRODUCTION: In recent years, there has been

A Novel Compact Band-pass Edge Coupled Microstrip Filter with
Defected Ground Structure (DGS)
Arjun Kumar, Ashwini K. Arya, M. V. Kartikeyan, Senior Member, IEEE
[email protected], [email protected], [email protected]
Millimeter Wave Laboratory, Department of Electronics & Computer Engineering
Indian Institute of Technology Roorkee, Roorkee-247667, Uttarakhand, India.
Abstract—In this paper, a novel compact band-pass edge
coupled microstrip filter is proposed with hexagonal
dumbbell shaped defected ground structure in ground
plane of 50Ω microstrip line. This provide better coupling
in pass band. Using DGS structure, Forward transmission
loss (S21) is -0.13 dB and return loss (S11) is -20 dB at the
centre frequency 5.4 GHz with wide bandwidth of 1.4
GHz. This type of filter can be used in WLANs and other
applications for the frequency range of 5-6 GHz. The
simulation is carried out in CST Microwave studio V9 full
wave EM simulator.
Index Terms—Band-pass edge coupled microstrip,
Hexagonal dumbbell shape DGS, wide bandwidth.
I. INTRODUCTION
Due to new emerging trends in the development of
technology in wireless communication system motivate
the requirement of band-pass filter with defected ground
structure, RF component, and Defected ground structure
(DGS) playing great role in size reduction [1]. Bandpass filter is very essential component of microwave
and mobile communication [2]. In this paper hairpin slot
with a notch in conducting strip with hexagonal
dumbbell shape DGS is proposed with low insertion
loss at center frequency 5.4 GHz. This DGS provide
better coupling. This edge coupled filter provide the
wide bandwidth, The defect in ground of planar
transmission lines (e.g. Microstrip, coplanar and
conductor backed coplanar waveguides) adds a parallel
connected inductor (L), Capacitor(C ) and Resistor(R )
to the circuit. This leads to a rejection of signal at a
certain frequency band i.e. determined by the shape of
defect in ground plane. Consequently this opens the
door to a wide range of applications [3].
II. L-C MODEL OF DGS UNIT CELL
The DGS consists of the two hexagonal areas and one
connecting slot in the ground plane.
(a)
(b)
Fig .1 DGS unit: (a) Dumbbell DGS unit, (b) L-C
equivalent of DGS.
Other geometries can also be used such as square head,
circular head and triangular heads etc for the defect in
the ground plane The DGS is considered as an
equivalent circuit consisting of capacitance and
inductance as given in the Fig. (1). The equivalent
inductive part increases due to the defect and produces
equivalently the high effective dielectric constant, that
is, slow wave property due to this fact the DGS line has
the longer electrical length than the standard Microstrip
line, for the same physical length. By varying the
various dimensions of the defect the desired resonance
frequency can be achieved. The resonance frequency for
this design is taken as 5.4 GHz. The filter quality factor
can be enhanced using this hexagonal shaped cavity
backed structure.
III. DESIGN CONFIGURATION
in Fig.4.(b) the gap (g) is increases, the S21 decreases in
less amount but the frequency shifted to the higher
frequency and after the optimization the dimension of
the proposed design the return loss (S11) is -20 dB and
the insertion loss (S21) is -0.13 dB which very low at 5.4
GHz, the optimize value of radius R=1.4 mm and Gap
g=1.6 mm.
In this proposed design the height of the substrate is
1.524 mm and relative permittivity 3.38 and the
conductor thickness 0.070 and loss tangent is 0.0009,
width of conducting strip is 4.7 mm and 18 mm and
proposed design as shown in Fig. 2.
Fig. 2 Proposed Bandpass filter (Top view)
The Transmission Line model is used to design
bandpass filter for resonant frequency 5.4 GHz. The
filter size 12.5mm × 18mm × 1.524mm is better
compatible for the different applications. The creation
of a Dumbbell shaped DGS in the ground plane of the
filter is used for the size reduction of the Bandpass filter
for working at the frequency of 5.4 GHz. From the
analysis
methods
the
filter
size
12.5mm × 18.0mm × 1.524 mm is calculated for the
frequency 5.4 GHz and is optimized with the CST
Microwave Studio V9 simulator[4], with the dumbbell
defect in the ground plane and the different parameter
shown in Fig.2 and their effects are studied, at bandpass
filter with this proposed design the critical parameters
are radius (R) , slot gap (g) and the hair pin slot between
the conducting strip and the effect of the notch or slit is
less so neglect the effect of the notch but it provides low
insertion loss at center frequency 5.4 GHz. The Fig.3 (a)
shows the effect of radius R variation, due the increase
in radius the return loss more negatively increases and
the resonant frequency is shifted towards higher
frequency and Fig.3. (b) Shows the variation of Gap (g),
as the gap increases frequency shifted towards the lower
frequency. The Fig. 4.(a) shows, as radius R increase
the insertion loss (S21) is decreases and the resonant
frequency also shifted towards the higher frequency and
.
(a)
(b)
Fig.3. Return Loss (S11): (a) Variation of R (b) Variation
of gap (g)
The Fig.5 shows the simulation results in S- parameters,
S11= -20 dB and S21= 0.13 dB at 5.4 GHz and the lower
3-dB cut-off frequency is 4.77 GHz and the Upper 3-dB
cut-off frequency is 6.18 GHz
IV. RESULTS & DISCUSSION
(a)
Fig.5 shows the return loss and insertion loss
characteristics at the resonance frequency of 5.4 GHz
with the wide band of 1.4 GHz. This proposed design
with simple structure using hexagonal dumbbell shape
DGS reduce the size of the filter simply using the 50Ω
microstrip line which provide the low insertion loss 0.13 dB in passband and provide the wide bandwidth.
Near about 98 % power is transmitted in the passband as
compared to the convention edge coupled bandpass
filter.
V. CONCLUSION
The design and simulation of the proposed bandpass
filter for wide band is carried out in this work. The
effect of dumbbell shaped DGS cell upon the size of
microstrip bandpass filter is shown and then the cavity
backed model is used for increasing the coupling effect
and the ultra wide bandwidth of the proposed Filter. The
performance characteristics of the proposed Filter
discussed and well compared to the conventional Filter.
(b)
Fig. 4.Insertion Loss (S21): (a) Variation of R (b)
Variation of gap slot (g)
REFERENCES
[1] Kim, C. S., J. I. Park, A. Dal, et al., “A novel 1-D periodic
defected ground structure for planar circuits,” IEEE
Microwave Guided Wave Lett, Vol. 10, No. 4, 131-133, 2000.
[2] A. Boutejdar, A. Batmanov1, A. Elsherbini, E. P. Burte1
and A. S. Omar, “A New Compact Tunable Bandpass Filter
Using Defected Ground Structure with Active Devices,” IEEE
Conference, 978-1-4244-2042-1/08,2008
[3] A.Batmanov, A.Boutejdar, A.Balalem, A.Omar, E.Burte,
F.Sabath et al.(eds.), “ New Coplanar Low pass Defected
Ground Structure (DGS) Filter,” Ultra-wideband short pulse
Electromagnetic 9, DOI 10-1007/978-0-387-77845_18@
Springer Science Business media, LIC 2010
[4] CST Microwave Studio V9.
Fig.5. Simulated Results with S-Parameters

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