A Novel LTCC Bandpass Filter for UWB Applications

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(IJCSIS) International Journal of Computer Science and Information Security,
Vol. 8, No. 8, November 2010

A Novel LTCC Bandpass Filter for UWB
Applications
Thirumalaivasan K and Nakkeeran R
Department of Electronics and Communication Engineering
Pondicherry Engineering College, Puducherry-605014, India
thirumalaivasank@pec.edu and rnakeeran@pec.edu

Abstract— Bandpass filter based on parallel coupled line gap size are required. Obviously, shrinking the gap size is not
microstrip structure is designed in low-temperature co-fired only the way to increase the coupling of coupled lines [10].
ceramic technology (LTCC) suitable for short range Ultra- The proposed bandpass filter in this paper is based on
Wideband (UWB) applications. Fifth order Chebyshev filter of LTCC using parallel coupling at center and broad side
0.05 dB passband ripple with fractional bandwidth of 62.17% is coupling at ends of the proposed filter structure. The filter is
proposed using insertion loss method. The filter demonstrates
designed to cover the entire UWB range. The main advantage
-10 dB bandwidth and linear phase response over the frequency
range 3.8 GHz - 7.4 GHz. With the above functional features, the of the multi-layered structure is to shrink the circuit size. The
overall dimension of the filter is 33.5 mm (height) × 1.6 mm obtained scattering parameters of UWB bandpass filter convey
(length) × 1.6 mm (breadth). It is not only compact but also an optimal performance in terms of insertion and return loss.
delivers excellent scattering parameters with the magnitude of It is distinctive in its structure and it has simple design with
insertion loss, |S21| lower than -0.09 dB and return loss better less number of design parameters compared to the existing
than -49 dB. In the passband, the computed group delay is well filter designs in the literature [11]-[13].
within the tolerable variation of 0.1 ns. The rest of the paper is organized as follows: In Section II,
the UWB bandpass filter design using LTCC is presented.
Keywords- Ultra-wideband; bandpass filter; parallel coupled Simulation results and analysis are presented in Section III.
line; low-temperature co-fired ceramic; group delay
Section IV concludes the paper.

I. INTRODUCTION
II. BANDPASS FILTER DESIGN

UWB technology has brought out tremendously increasing
research interests since the Federal Communications Figure 1 shows one possible circuit arrangement for
Commission (FCC) in USA released its unlicensed use for bandpass filter using parallel coupled line microstrip structure
indoor and hand-held systems in 2002 [1]. Efforts have been at center and broad side coupling at end of the geometry
made in the past eight years towards exploring various UWB designed in LTCC for UWB range. It consists of transmission
components and devices. As one of the essential component line sections having the length of half wavelength at the
blocks, the researchers are attempting to design the UWB corresponding center frequency. Half wavelength line
bandpass filter (BPF) with 120% fractional bandwidth resonators are positioned so that adjacent resonators are
centered at 6.85 GHz. In the recent years, the market pays parallel to each other along half of their length. This parallel
much attention towards miniaturization of receiver systems. arrangement gives relatively large coupling for the given
Hence, researchers are working for the development of small spacing between the resonators, and thus, this filter structure is
size and cost effective filters [2]-[5]. particularly convenient for constructing filters having larger
Parallel coupled-line microstrip filters are found to be one bandwidth as compared to the other structures [14]-[17].
of the most commonly used microwave filters in many
practical wireless systems for several decades [6]-[8]. In
addition to the planar structure and relatively wide bandwidth,
the major advantage of this kind of filter is that its design
procedure is quite simple. Based on insertion loss method [9],
filter functions of maximally flat and Chebyshev type can be
easily synthesized. Moreover, the filter performance can be
improved in a straightforward manner by increasing the order
of the filter. When these filters are to be realized by parallel
coupled microstrip lines, one of the main limitations is the
small gap size of first and last coupling stages. To increase the
coupling efficiency, more fractional bandwidth and smaller Figure 1. Geometry of the proposed UWB bandpass filter

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ISSN 1947-5500
(IJCSIS) International Journal of Computer Science and Information Security,
Vol. 8, No. 8, November 2010
The gap between the resonators is introducing a capacitive
coupling, which can be represented by a series capacitance.
The broad side coupling and existence of the substrate result
tight coupling, which provides wide bandpass operation. The
physical parameters of the proposed bandpass filter are
optimized to the following values, l1=5.89 mm; l2=5.86 mm;
d=0.2 mm; g0 = 0.08 mm; g1 = 0.1 mm; a0 = 1.06 mm;
a1 = 1.2 mm; a2 = 1.02; w0 = 1.6 mm; b = 1.6 and h = 33.5 mm
to cover the entire UWB range between 2 GHz and 9 GHz.
Using this configuration, higher coupling is obtained and
therefore wider bandwidth is achieved. This structure is used
to generate a wide passband and expected to achieve a tight
coupling, and lower insertion by reducing both strip and slot
width. 3D view of a LTCC UWB bandpass filter with parallel
and broadside coupling is shown in Figure 2, which consists of
two layers, resonators and substrate with frames.

Figure 3. Simulation S- parameters

Figure 2. 3D view of proposed LTCC filter structure

III. RESULTS AND DISCUSSION
The proposed filter is designed to provide a wide passband,
low insertion loss and return loss, linear phase over the
passband, flat group delay and high fractional bandwidth.
The simulation S parameters of the proposed UWB bandpass
filter using LTCC are shown in Figure 3. It is clear from the
Figure 4. Simulation group delay
response that the proposed filter has better insertion loss of -
0.09 dB and the low return loss of about -49 dB. The -10 dB
fractional bandwidth computed from the response is about
62.17 %.
For wideband applications, the examination of the flat group
delay is essential and required. The simulation group delay for
the proposed filter is shown in Figure 4, which exhibits a flat
group delay response below 0.1 ns over the whole passband. It
implies that this proposed UWB filter has a very good linearity
of signal transfer and would ensure the minimum distortion to
the input pulse when it is implemented in the UWB system.
The response of the Figure 5 shows that the phase of S21
throughout the -10 dB passband between 3.8 GHz and
7.4 GHz of designed filter is acceptably linear.
In order to evaluate the performance of the proposed UWB
bandpass filter, the filter is simulated through the simulation
tool, IE3D [18]. The filter is designed based on LTCC
substrate with two upper sheet layers, thickness of 1.6 mm and
1.93 mm with dielectric constant of 7.8 and a loss tangent of Figure 5.Simulation of phase of S21
0.002.

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(IJCSIS) International Journal of Computer Science and Information Security,
Vol. 8, No. 8, November 2010
CONCLUSION [12] Thirumalaivasan K and Nakkeeran R, ―Wired Ring Resonator
Based Compact Ultra-Wideband Bandpass Filters Using Dual-line
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In this letter, a bandpass filter for UWB applications Conference on Control, Communication and Power Engineering
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[13] J.-T. Kuo, ―Accurate quasi-TEM spectral domain analysis of single
demonstrated an excellent ultra-wide bandwidth from 3.8 GHz and multiple coupled microstrip lines of arbitrary metallization
to 7.4 GHz. Total size of the UWB filter is 33.5 mm (height) × thickness,‖ IEEE Trans. Microwave Theory Tech., MTT-43, no.8,
1.6 mm (length) × 1.6 mm (breadth) and the fractional pp. 1881-1888, Aug. 1995.
bandwidth is about 62.17 %. Simulation of bandpass filter [14] Thirumalaivasan K, Nakkeeran R, and Oudayacoumar S, ―Circular
Resonator Based Compact Ultra-Wideband Bandpass and Notched
delivers excellent scattering parameters with magnitude of Filters with rejection of 5-6 GHz band‖, in the Proc. of ACEEE
insertion loss, |S21| lower than -0.09 dB and return loss better International Conference on Control, Communication and Power
than -49 dB. The obtained group delay for this filter is below Engineering CCPE 2010, July 28. DOI: 02.CCPE.2010.1.212.
0.1 ns. [15] Yue Ping Zhang and Mei Sun, ―Dual Band Microstrip Bandpass
Filter Using Stepped Impedance Resonators With New Coupling
Schemes,‖ IEEE Trans. on Microwave Theory and Tech., vol.54,
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―Effective Notch Ultra-Wideband Filter Using Ring Resonator for
the Rejection of IEEE 802.11a‖, in the Proc. of IEEE International
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[3] C.Q.Scrantom and J.C.Lawson, ―LTCC Technology where we are
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and where we’re going-II‖, In IEEE MTT Int. Microwave. Symp.
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[4] C.W.Tang,‖Harmonic Suppression LTCC Filter with the Step
[18] IE3D 14, Zeland Software, Ins., Fremont, USA
Impedance Quarter Wavelength Open stub‖, IEEE Trans. Microw.
Theory Tech., vol. 51, no. 10, pp. 2112–2118, Oct. 2003.
[5] Jorge A. Ruiz Cruz, Yunchi Chang, Kawthar A. Zaki, Andrew
J.Piloto and Joseph Tallo,‖Ultra-Wideband LTCC Ridge AUTHORS PROFILE
Waveguide Filters,‖ ," IEEE Microw. Wireless Compon. Lett., vol.
17, no. 2, pp. 111-117, Feb. 2007. Mr.K.Thirumalaivasan was born in India. He received the B.Tech. degree in
[6] Jen-Tsai Kuo, Wei-Hsiu Hsu, and Wei-Ting Huang,‖ Parallel Electronics and Communication Engineering from Pondicherry University,
Coupled Microstrip Filters with Suppression of Harmonic Puducherry, India, and the M.E. degree in Communication Systems from
Response,‖ IEEE Microw. Wireless Compon. Lett., vol. 12, no.10, College of Engineering Guindy, Anna University, Chennai, India, in 2004 and
Oct. 2002. 2007 respectively. He is currently working towards the Ph.D. degree at
[7] L. Zhu, S. Sun, and W. Menzel, "Ultra-wideband (UWB) bandpass Pondicherry Engineering College, Pondicherry. His current research interest is
filters using multiple-mode resonator," IEEE Microw. Wireless in the area of UWB filters and narrowband interference issues with UWB
Compon. Lett., vol. 15, no. 11, pp. 796-798, Nov. 2005. systems.
[8] Hussein Shaman, Jia-Sheng Hong,‖ Asymmetric Parallel-Coupled
Lines for Notch Implementation in UWB Filters,‖ IEEE Microw.
Wireless Compon. Lett., vol. 17, no.7, July 2007. Dr. R. Nakkeeran Received BSc. Degree in Science and B.E degree in
[9] Pozar, D. M., Microwave Engineering, Wiley, New York, 1998. Electronics and Communication Engineering from the Madras University in
[10] T.-N. Kuo, S.-C. Lin, and C. H. Chen, ―Compact ultra-wideband 1987 and 1991 respectively and M.E degree in Electronics and
bandpass filters using composite microstrip-coplanar-waveguide Communication Engineering (diversification in Optical Communication) from
structure,‖ IEEE Trans. Microw. Theory Tech., vol. 54, no. 10, pp. the Anna University in 1995. He received Ph.D degree from Pondicherry
3772–3777, Oct. 2006. University in 2004. Since 1991, he has been working in the teaching
[11] Oudayacoumar S, Nakkeeran R and Thirumalaivasan K, profession. Presently, he is Associate Professor in Pondicherry Engineering
―Resonator Based Compact Ultra-Wideband and Notched College. He is life member of IETE, ISTE, OSI and IE (I). Also he is member
Wideband Filters”, in Proceedings of the IEEE National of OSA, SPIE and IEEE. He has published seventy five papers in National and
Conference on Communication (NCC 2010), at IIT Chennai, International Conference Proceedings and Journals. He has co-authored a
January 29-30, 2010. DOI:10.1109/NCC.2010.5430168. book, published PHI. His areas of interest are Optical Communication,
Networks, Antennas, Electromagnetic Fields and Wireless Communication.

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