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Design of DMB Nonuniform BPF Using LTCC
Sung-kyo Park
Dept of Electronic Engineering University of Chosun, 501-759
Gwangju, Korea [email protected]
Abstract. Recently, RF systems have rapidly grown with the
extension of the mobile communication service. The mobile service
companies are providing the satellite broadcasting and common usage
are expected. Coinciding with current trend, the development of
improved satellite DMB (Digital Multimedia Broadcasting) tuner is
required. To improve the receiving sensitivity under the poor
communication circumstance, it is necessary to design the LNA (Low
Noise Amplifier) with outstanding low noise characteristic and the
BPF (Bandpass Filter) to transmit only desired signal without
distortion and loss. Besides high reliability, the miniaturization
and lightweight are required for design of mobile terminals. In
this paper, we designed and fabricated DMB nonuniform SIR-type BPF
with embedded tunable pads, which operates at 2642 ㎒ and is
embedded in the substrate of RF module of a tuner with LTCC. As a
result, we obtained the passband insertion loss of 2.4 dB and the
passband ripple of 0.08 dB. So this BPF is applicable to RF module
of a satellite DMB tuner. 1 Introduction Recently, RF systems have
rapidly grown with the extension of the mobile communication
service. Through first generation of analog mobile communication
and second generation of digital mobile communication, there comes
third generation of mobile communication which offers service of
sound, data, and image, etc.. Now, coinciding with current trend,
the mobile service companies are providing satellite broadcasting
to subscribers. Also, keeping pace with the mobile communication
service, the development of improved satellite DMB (Digital
Multimedia Broadcasting) tuner is required. Here, Satellite DMB is
digital multimedia broadcasting which offers service of sound, data
and image of high quality, and also offers superior fixed and
mobile receiving quality. Satellite DMB transmits data from ground
to satellite using satellite frequency. Then, satellite transmits
data to mobile phones or personal terminals using frequency of 2642
㎒ in S band. So, it is very important to receive the feeble signal
without noise and distortion on satellite communication. Because
noise and reflection coefficient of amplifier affect the whole
system, these are very important in the mobile · wireless ·
satellite communication. To improve the receiving sensitivity under
the poor communication circumstance, it is required to design the
LNA (Low Noise Amplifier) with outstanding low noise characteristic
and the BPF (Bandpass Filter) to transmit only desired signal
without distortion and loss [1]-[3]. Besides the miniaturization,
lightweight, and high reliability RF systems which satisfy these
conditions are required.
In this paper, we designed nonuniform SIR-type BPF with embedded
tunable pads applicable to RF module of a satellite DMB tuner
[4]-[7]. And, to fabricate miniature
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and lightweight RF module we embedded this BPF in the substrate
of RF module using LTCC. Then, we analyzed and examined the
capability of application to RF module of a satellite DMB tuner. 2
Stripline SIR 2.1 Uniform Impedance Resonator and Stepped Impedance
Resonator The most typical transmission-line resonators are coaxial
resonators and stripline resonators. These resonators possess a
wide applicable frequency range starting at several 100 ㎒ extending
to around 100 ㎓, and presently remain the most common choice for
filters in wireless communication. These resonators do not possess
low loss properties, i.e., they do not have high Q values compared
to waveguide or dielectric resonators. However, they have valuable
features as electromagnetic wave filters: a simple structure, a
small size, and the capability of wide application to various
devices. Moreover, the most attractive feature of micro-stripline,
stripline or coplanar-line resonators is that they can be easily
integrated with active circuits such as MMICs.
Fig. 1 shows the fundamental structure of a micro-stripline
half-wavelength resonator with two open-circuited ends. This figure
shows the physical structure of the resonator: a strip conductor of
uniform width and a length equivalent to half-wavelength, formed on
a dielectric substrate. This structure can be expressed in
electrical parameters as a transmission line possessing uniform
characteristic impedance with an electrical length of π radian.
Such transmission-line resonators will be referred to as uniform
impedance resonator (UIR). General requirements for UIR intended
dielectric substrate materials include a low loss tangent, high
permittivity, and temperature stability. Transmission-line
resonators are widely used because of their simple structure and
easy-to-design features. In practical design, however, such
resonators have a number of intrinsic disadvantages, such as
limited design parameters due to their simple structure. Other
electrical drawbacks include spurious responses at integer
multiples of the fundamental resonance frequency. To overcome these
problems, it is a common practice in the VHF band to load
capacitors at both open-ends of the resonator. By doing so, the
resonator length is shortened and spurious resonance frequencies
are consequently shifted from the integer multiples of its
fundamental frequency. Fig. 2 shows the structural variations of a
half-wavelength type resonator.
The capacitors loaded UIR shown in Fig. 2(b) has a
characteristic impedance of Z1 and an electrical length of 2θ1.
When the angular resonance frequency ωo of this resonator
corresponds to that of a half-wavelength UIR shown in (a), the
loading capacitance C is expressed as follows:
C = Y1 tanθ2 /ωo (1) Where, Y1=1/Z1 and θ2 = π /4 - θ1
Looking from a different point of view, by replacing both θ2
length transmission
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line components in (a) with lumped-element capacitors C as in
(b), the two circuits are equivalent. The capacitor loaded UIR
possesses the advantages of a small size and the capability of
spurious response suppression. However, it is not always easy to
apply the capacitor loaded UIR to frequency regions above 1 ㎓,
because the circuit loss of the lumped-element capacitor C
increases dramatically as does the variance of resonance frequency,
thus requiring frequency adjustment. The loaded capacitance C can
be replaced by an open-circuited transmission line. Furthermore, it
is not always necessary to design the characteristic impedance of
the transmission line at Z1. An example is shown in Fig. 2(c),
where the characteristic impedance is designed at Z2 (=1/Y2). When
21'2tan2 θθ YY = , all three resonators will resonate at the same
frequency. In this case, if, Z2
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Fig. 2. Various types of half-wavelength resonator
Ground via-holes as shown in Fig. 3 are essential for 4/gλ type
SIR of a stripline
configuration. This necessity raises inevitable problems such as
increased losses and resonance frequency shifts caused by the
parasitic components generated near via-holes. For this reason the
application of 4/gλ type SIR is limited to filters of special use
where, for example, miniaturization is prior to low insertion
losses. Generally speaking, open-ended 2/gλ type SIR possess a far
wider applicable range, thus are more available for RF and
microwave circuits. Since stripline and micro-stripline resonators
are formed on dielectric substrate, the use of a dielectric
material with high permittivity proves to be most effective for
miniaturization of filters. A stripline resonator, which has a
tri-plate structure, possesses the same wavelength reduction factor
as a coaxial resonator, whereas in the case of micro-stripline the
reduction factor decreases due to the inhomogeneous dielectric
medium.
The unloaded Q of stripline and micro-stripline resonators is
dependent on the line width and the substrate thickness, and it
becomes difficult to design high Q value resonator as compared to a
coaxial type structure. This is because the center conductor of a
coaxial resonator possesses a large surface area along with a
uniform current distribution, whereas in the case of a stripline
structure, ohmic losses are apt to increase due to the current
concentration at the edges of the stripline center conductor.
However, the stripline SIR has a distinct feature that allows for
cost-efficient fabrication of various complicated structures due to
a manufacturing process based on thick film and/or thin film
processing technology. Thus, stripline SIR is an available resource
for filters which call for small size rather than low losses, and
for microwave circuits requiring integration to active devices.
Parallel coupled-lines are applied to obtain interstage coupling
between resonators. In the case of SIR, the coupling circuit is
electrically expressed as two pairs of coupled-lines as shown in
Fig. 4. This circuit differs from that of the UIR. Coupled-lines 1
including a short-circuited section can be analyzed by even- and
odd-mode impedance, Z0e1, Z0o1 and coupled line length θ1 .
Inductive coupling is
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Fig. 3. Basic structure of a micro-stripline SIR
dominant in this portion due to a large current flow near the
short-circuited point. Coupled-lines 2 includes the open-end of the
resonator, its electrical parameters being defined as Z0e2, Z0o2,
and θ2 . Capacitive coupling is dominant in this portion due to a
high voltage near the open-end. Z1 and Z2 for single transmission
line SIR are given as the geometric means of even- and odd-mode
impedance as
10101 oZeZZ •= , 20202 oZeZZ •= (2)
Thus, the even- and odd-mode impedance cannot be determined
independently. Two pairs of coupled lines enable a more flexible
design, while on the other hand this becomes a disadvantage because
the coupling circuits cannot be determined uniquely.
From a practical point of view, a stripline SIR-type BPF is
suitable for filters which require miniaturization as the top
priority. Fig. 5 shows a two-stage BPF using stripline SIR. By
employing tapping couplings for the input and output terminals and
eliminating any additional components, this filter can be realized
by using LTCC.
Fig. 4. Interstage coupling structure of stripline SIRs
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144 Design of Dmb Nonuniform Bpf using Ltcc
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Fig. 5. Structure of a stripline BPF
3 Design of BPF We designed DMB nonuniform SIR-type BPF with
tunable pads using LTCC, to satisfy the specifications shown in
Table Ⅰ and to be embedded in the substrate of RF module. We
obtained the length of coupled line, width, and gap using Designer
(Ansoft Co.). After passing through optimization step, we did
electromagnetic (EM) simulation using HFSS (Ansoft Co.) to confirm
performance of the designed BPF. The designed BPF of which size is
5 mm * 6 mm consists of 4-plate structure. There is 3 dimensional
structure of BPF in Fig. 6. For this BPF we selected Dupont 951 as
LTCC sheet. It has thickness of 360 um, tangent loss of 0.0045,
dielectric constant of 7.8, and conductor thickness of 7 um. Fig. 7
shows simulation results of insertion loss and return loss of
designed BPF.
Table 1. SPECIFICATIONS OF BPF
Parameter Specification Center Frequency (Fo) 2642.0 ㎒
Passband Width Fo ± 10.0 ㎒ Passband Insertion Loss 2.5 ㏈max.
Passband Ripple 1.0 ㏈max. Attenuation (absolute value) at 1525.0
㎒ ~ at 2160.0 ㎒
at 2450.0 ㎒ at 3350.0 ㎒
25.0 ㏈min. 25.0 ㏈min. 20.0 ㏈min.
Fig. 6. The 3 dimensional structure of the designed BPF
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Fig. 7. Simulated insertion loss and return loss of the designed
BPF
4 Experiment and Discussion We fabricated BPF which is embedded
in the substrate of RF module using LTCC. We measured the
characteristics of fabricated BPF using E5071B ENA series network
analyzer (Agilent Co.). The measured and simulated results of BPF
are shown in Fig. 8. Here, attenuation increased were 2 dB at 2450
㎒ and 13 dB at 2160 ㎒ compared to the designed results, but
insertion loss was 0.4 dB higher. The characteristics of BPF are
summarized in Table Ⅱ. 5 Conclusion In this paper, we designed and
fabricated nonuniform SIR-type BPF with tunable pads applicable to
the RF module of a satellite DMB tuner. The specifications were
decided to satisfy good receiving performance in the inner of DMB
terminal and this BPF was embedded in the substrate using LTCC for
the miniaturization of RF module.
As a result, at center frequency of 2642 ㎒ we obtained the
passband insertion loss of 2.4 dB and the passband ripple of 0.08
dB compared to the specifications of the passband insertion loss of
2.5 dB and the passband ripple of 1 dB, and they satisfied the
required and the designed specification of BPF. If the more
miniature BPF can be fabricated and embedded in substrate using
LTCC and also the passband insertion loss of BPF can be reduced
through optimization step, this BPF can be applied to RF module of
a satellite DMB tuner.
(a) Passband insertion loss
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146 Design of Dmb Nonuniform Bpf using Ltcc
GESTS-Oct.2005
(b) Passband return loss
Fig. 8. Designed and measured result of BPF
Table 2. THE CHARACTERISTICS OF BPF
References
[1] L. Young, Microwave Filters Using Parallel Coupled Lines.
Dedham, Massachusetts: Artech House Inc., 1972.
[2] G. L. Matthaei, L. Young, and E. M. T. Jones, MICROWAVE
FILTERS, IMPEDANCE-MATCHING NETWORKS, AND COUPLING STRUCTURES.
Dedham, MA: Artech House Inc., 1980.
[3] B. C. Wadell, Transmission Line Design Handbook. Norwood,
MA: Artech House Inc., 1991.
[4] S. Uysal, Nonuniform Line Microstrip Directional Couplers
and Filters. Norwood, MA: Artech House Inc., 1993.
[5] J. S. Hong and M. J. Lancaster, Microstrip Filters for
RF/Microwave Applications. New York: John Wiley & Sons, Inc.,
2001.
[6] Ching-Wen Tang, “Harmonic-suppression LTCC filter with the
step-impedance quarter-wavelength open stub,” Microwave Theory and
Techniques, IEEE Transactions on, vol. 52, Issue 2, pp. 617-624,
Feb. 2004.
[7] Gyu-Je Sung, Dong-Hun Ye, and B. Kim, “Equivalent circuit
design of multilayer parallel-coupled line filter,” Radio and
Wireless Conference, 2004 IEEE, pp. 239-241, Sept. 2004.
Parameter Specification Design Measurement
Center Frequency (F0) 2642.0 ㎒ 2642.0 ㎒ 2642.0 ㎒
Passband Width F0 ± 10.0 ㎒ F0 ± 10.0 ㎒ F0 ± 10.0 ㎒
Passband Insertion Loss 2.5 ㏈max. 2.0 ㏈ 2.4 ㏈
Passband Ripple 1.0 ㏈max. 0.12 ㏈ 0.08 ㏈ Attenuation ( absolute
value) at 1525.0 ㎒ ~ at 2160.0 ㎒ at 2450.0 ㎒ at 3350.0 ㎒
25.0 ㏈min. 25.0 ㏈min. 20.0 ㏈min.
23.0 ㏈ 27.0 ㏈ 22.0 ㏈
36.0 ㏈ 29.0 ㏈ 30.0 ㏈
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Biography
▲ Name: Sung-kyo Park Address: #375 Seosuk-dong, Dong-gu,
Gwangju 501-759 Korea Education & Work experience: 1996. 2 :
Ph. D. Dept of Electrical Engineering,
University of Chosun 1994. 3 - : Lecturer, Dept of Electronic
Engineering,
University of Chosun 2001. 3 - : Professor, Dept of Electronic
Engineering,
University of Chosun Tel: +82-62-2307860 E-mail:
[email protected]
