DESIGN AND ANALYSIS OF COMPACT UWB BAND PASS FILTER

International Journal of Electromagnetic ( IJEL ), Vol 2, No 1
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DESIGN AND ANALYSIS OF COMPACT UWB BAND
PASS FILTER
Satish Chand Gupta, Mithilesh Kumar and Ramswaroop Meena
University college of Engineering,
Rajasthan Technical University, Kota, Rajasthan, India
ABSTRACT
This paper presents design, implementation and analysis of an ultra-wideband (UWB) band-pass-filter
using parallel-coupled microstrip line with defective ground plane and a uniform multi-mode resonator.
The structure of the filter is designed on microwave substrate GML 1000 of dielectric constant 3.2 and
height is 0.762 mm. Simulation is carried out by CST MSW software and optimized structure is
fabricated. The frequency response is measured on vector analyzer and measured results show close
approximation with simulation results. In this article modeling of the proposed filter is also reported. The
electric model of the filter is analyzed by circuit theory and MATLAB. This model is validated by
comparing the results with the CST simulation and VNA measured results. This filter is compact in size of
dimension 30˟1.87 mm2 may be useful for modern wireless application of communication.
KEYWORDS
Multi-mode resonator (MMR), Fractional bandwidth (FBW), Ultra-wide band (UWB), Band pass filter
(BPF), Parallel-coupled microstrip line (PCML).
1. INTRODUCTION
In 2002, Federal Communication Commission (FCC) released Ultra-wide band (UWB) system
from 3.1 GHz to 10.6 GHz for the use of indoor and hand-held systems. Ultra- wideband
(UWB) band pass filters play a key role in the development of UWB systems [1]. After the
release of UWB, there were lot of challenges to design such a band pass filter, with a pass band
of the frequency range (3.1 GHz - 10.6 GHz), and a fractional bandwidth of 110% by
conventional method of filter design. Initially broad band filters were designed, and covered
only 30 to 40 % of UWB not the whole UWB [2].In [3-7] many researchers reported various
techniques, like aperture compensation, microstrip-coplanar waveguide structure design, ground
plane aperture technique and multiple-mode resonator were used to design UWB filters. Many
new techniques [8-13], like U-shaped slot coupling [8], asymmetric parallel-coupled lines [9],
right/left-handed transmission line [10], differential- mode wide band BPF using two stage
branch-line structures with open circuited stubs [11], tunable harmonic stepped-impedance
resonators [12] and parallel coupled line microstrip structure [13] were used to design the UWB
filters.
In this paper a design and analysis of a compact UWB filter is presented. In section 2, design
and development of the UWB filter using double PCML, MMR and DGS is demonstrated.
Small size stubs at input and output end are used for impedance matching to improve the
performance of the filter. The electrical analysis of the filter is mentioned in section 3. Finally
paper is concluded in section 4.

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2. DESIGN OF UWB FILTER
The layout of the proposed structure is shown in Fig.1 which consists two parallel coupled
microstrip line (PCML) of quarter wave length with a rectangular shaped DGS and a uniform
multi-mode resonator (MMR). The designed structure of filter is simulated and optimized by
using CST Microwave Studio software by using microwave laminate GML 1000 of dielectric
constant 3.2, height h = 0.762 mm and loss tangent 0.001. The design parameters of the
proposed filter are mentioned in Table I.
Fig.1 Schematic of UWB filter
Table I: Design parameters of the UWB filter
Notation Parameters of the filter Dimensions
in( mm)
b Width of the feed line 1.83
a Length of the feed line 10.5
c Width of the stub 0.32
d Length of the stub 1.87
e Width of the PCML 1.71
f Length of PCML 6.94
g Length of MMR 11.32
h Width of MMR 1.71
i Length of DGS 6.74
j Height of DGS 6.5
k Spacing between PCML 0.11
The optimized filter is fabricated by conventional photo lithographic process and the photograph
of the fabricated filter is shown in Fig.2. The frequency response of the fabricated filter is
measured on Agilent Tech. E5071C ENA Vector Network Analyzer. The measured frequency
response is compared with the simulated frequency response which is shown in Fig.3.The
comparison results shown in Fig.3 are in close approximation to each other. The measured
results show insertion loss S21 of value better than -2.0 dB and return loss better than -10.0 dB
in the frequency range from 3.1 GHz to 10.6 GHz. A slight mismatch between measurement and
simulation result is due to the imperfection in measurement, fabrication process and the quality
of the substrate used.

3
(a) (b)
Fig.2 Photo graph of fabricated filter (a) Top view (b) bottom view
Fig.3 Comparison of frequency responses
3. ELECTRICAL ANALYSIS OF THE UWB FILTER
The electrical analysis of the proposed filter is carried out by making electrical equivalent of the
filter. The S-parameters of the electrical equivalent circuit is obtained by circuit theory. The
frequency response of this electrical equivalent is obtained by MATLAB and, it is compared
with the simulation results to justify the topology used to make the equivalent circuit of the
filter. The parallel coupled microstrip line with DGS, MMR and feed lines are the basic
components of the filter circuit. The overall electrical equivalent of this UWB filter can be
obtained by combing the equivalent circuit of individual components of the filter circuit.

4
3.1 Equivalnt Circuit of Feed Line
Microstrip line 50 ohm transmission line can be represented by distributed R, L, C and G
elements. At very high frequency in GHz range, resistive and conductive components can be
neglected and line is represented by reactive elements. A small section of feed line of 50 ohm
impedance can be represented by an inductance. Simulation results of physical line are
compared with its equivalent circuit simulation results is shown in Fig.4.
(c)
Fig.4 (a) Small section of feed line 50 ohm (b) Equivalent circuit of feed line of L0=0.8215 nH (c)
Comparison of results
3.2 Equivalent Circuit of Pcml
Parallel coupled microstrip line equivalent circuit can be explained by two mutually coupled
inductors and capacitors between line and ground [13]. L1 & L2 are self-inductance of the lines
and K12 is coupling coefficient between the lines. Capacitance between the line and ground are
indicated by C1 & C2 values. Comparison between the circuit simulation and physical line
simulation results is shown in Fig.5.

5
(a) (b)
(c)
Fig.5 (a) Physical line (b) Electrical Equivalent circuit of PCML(L1 = L2 = 3.58nH and K12 = 0.613) (c)
Comparison of results
The multi-mode resonator in microstrip structure is represented by an inductor. The overall
equivalent circuit of the UWB filter can determine by including the equivalent circuit of the
individual components of the filter, and it is shown in Fig.6
Fig.6 Electrical equivalent circuit of the UWB filter where L3 is assumed of value 1.81nH

6
The electrical equivalent circuit of the filter shown in Fig.6 is simulated on SERENIDE SV
8.5 circuit simulator and its frequency response is shown in Fig.7.The equivalent circuit shown
in Fig.7 can be simplified by considering two circuits connected in cascade fashion shown in
Fig.8.
Fig.7 Frequency response of electrical equivalent circuit of UWB filter.
3.3 Electrical Analysis of the Uwb Filter
The equivalent circuit of the UWB filter shown in Fig.6 can be analyzed by simple network
theory. The overall equivalent circuit is divided into two symmetrical circuits by splitting the
middle inductor into half of its value which is shown in Fig.7 the simplified version of the
equivalent circuit is shown in Fig.9.
Fig.8 Symmetrical equivalent circuit of UWB filter

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Fig.9 Simplified equivalent circuit of UWB filter
The circuit shown in Fig.8 can be considered as cascaded connection of two networks. Overall
[ABCD] parameters of the circuit are calculated by matrix multiplication of [ABCD] parameters
of each network.
Fig.10 Network Equivalent circuit of the UWB filter
The overall ABCD parameters obtained by equation 1 are converted into S-parameters by
the following equations
The S-parameters obtained from equation 2&3 are calculated by using MATLAB and
simulation results are compared with CST simulation results and the SERENIDE circuit
simulation results. The close resemblance among the results shown in Fig.11 verifies the
proposed method of obtaining equivalent circuit of the filter.

8
(a)
(b)
Fig.11 Comparison of results (a) Return loss (S11) (b) Insertion Loss (S21)
4. CONCLUSIONS
A microstrip line UW BPF filter using parallel coupled microstrip line and multi-mode
resonator is presented in this paper. For demonstration the UWB BPF is designed, simulated
and fabricated. The measured frequency response of the filter shows band pass behavior in
frequency range from 3.1 GHz to 10.6 GHz with insertion loss less than -2.0 dB and return loss
better than -10.0 dB. The electrical equivalent circuit of the filter is also reported is this paper.
The proposed filter may be useful for wireless communication systems.

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REFERENCES
[1] “Revision of Part 15 of the Commission’s Rules Regarding Ultra-Wide-band Transmission
Systems,” First Note and Order Federal Communications Commission, ET-Docket 98-153, 2002.
[2] S. Sun and L. Zhu, “Multiple-mode-resonator-based band pass filters for ultra wide band
transmission systems,” IEEE Microw. Mag., Vol.10, No.2, pp. 88-98, Apr. 2009
[3] L. Zhu, H. Bu, and K. Wu, “Aperture compensation technique for Innovative design of ultra-
broadband microstrip band pass filter,” IEEE MTT-S Int. Dig., vol. 1, 2000, pp. 315-318
[4] W. Menzel, L. Zhu, K. Wu, and F. Bogelsack, “On the design of novel compact broad-band planar
filters,” IEEE Transaction on Microwave Theory Technology,Vol. 51, No. 2, pp. 364-370, Feb.
2003
[5] Li K, Kurita D, Matsui T, “An ultra-wideband band pass filter using broadside- coupled microstrip-
coplanar waveguide structure,” IEEE MTT-S, Int. Dig., June 2005, pp. 675-678
[6] L. Zhu, H. Bu and K. Wu “Broadband and compact multi-pole microstrip band pass filters using
ground plane aperture technique,” IEE proc. Microwave Antennas Propag., Vol. 149, No.1, pp.71-
77, 2002
[7] L. Zhu, S. Sun, and W. Menzel "Ultra-wideband (UWB) band pass filters using multiple-mode
resonator,” IEEE Microwave and Wireless Components Letters, Vol. 15, No.11, November 2005,
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[8] D. Packiaraj, K. J. Vinoy, and A. T. Kalghatgi, “Analysis and design of a compact multi-layer ultra
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[9] X. Q. Chen, L. H. Weng, Y. C. Guo, and X. W. Shi, “RF circuit design integrated with microstrip
DGS,” Progress in Electromagnetic Research M. Vol.3, pp.141-152, 2008
[10] Hang Wang and Lei Zhu, “Aperture-backed microstrip line multiple-mode resonator for design of a
novel UWB band filter,” IEEE APMC Proceedings pp.4, Dec., 2005
[11] C.-P. Chen, Z. Ma and T. Anada, “Synthesis of ultra-wide band pass filter employing parallel-
coupled stepped-impedance resonators,” IET Microwaves,Antennas and Propagation, Vol. 2, No. 8,
pp. 766-772, Dec., 2007
[12] L. H. Weng, Y. C. Guo, X. W. Shi, and X. Q. Chen, “An overview on defected ground structure,”
Progress In Electromagnetic Research B, Vol.7, pp.173–189, 2008
[13] Ya. A. Kolmakov and I. B. Vendik, “Compact ultra-wideband band pass filter with defected ground
plane,” IEEE 2005 European Microwave Conference, Vol.1, 2005

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