2008 IEEE INTERNATIONAL RF AND MICROWAVE CONFERENCE PROCEEDINGS 2008 IEEE INTERNATIONAL RF AND MICROWAVE CONFERENCE PROCEEDINGS 2008 IEEE INTERNATIONAL RF AND MICROWAVE CONFERENCE PROCEEDINGS 2008 IEEE INTERNATIONAL RF AND MICROWAVE CONFERENCE PROCEEDINGS December 2December 2December 2December 2----4, 2008, Kuala Lumpur, MALAYSIA4, 2008, Kuala Lumpur, MALAYSIA4, 2008, Kuala Lumpur, MALAYSIA4, 2008, Kuala Lumpur, MALAYSIA

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The microstrip coupled line bandpass filter using LTCC technology

for 5GHz wireless LAN application

Zulkifli Ambak, Rosidah Alias, Azmi Ibrahim, Sabrina Mohd Shapee, Mohd Zulfadli

Mohammed Yusoff, Muhammad Redzuan Saad, Mohamed Razman Yahya and

Abdul Fatah Awang Mat

Microelectronics and Nano Technology Program, TM Research & Development Sdn. Bhd.,

TMR&D Innovation Centre, Lingkaran Teknokrat Timur, 63000, Cyberjaya,

Selangor Darul Ehsan.

E-mail: zulkifliambak@tmrnd.com.my

Abstract – This paper presents a top-down design of

the microstrip coupled line Band pass filter (BPF)

embedded in low temperature co-fired ceramic

(LTCC) for 5GHz wireless LAN applications. It

includes the design, simulation, fabrication and

measurements. The filter circuit was designed and

simulated based on Agilent Advanced Automation

(ADS2005A) software. Then, the physical dimensions

of components and the filter itself is subsequently

determined and the physical design is later performed

in the layout window of Empire XcCEL. All measured

simulations are analyzed and compared to design

specifications and characteristics (curve fitting). Any

inaccuracy is taken into account where corrected

design is further recovered.

Keywords:Low Temperature co-fired ceramics(LTCC),

microstrip band passs filter (BPF)

1. Introduction

The low temperature co-fired ceramic

(LTCC) is a ceramic substrate system which is

applicable in electronic circuits. For

telecommunication applications, LTCC enables the

integration of passive components and functions, such

as filtering and antennas up to millimeter wave

frequencies. Presently, the importance of LTCC is

becoming more prominent in view of the fact that a lot

of many organizations has been funding R&D project

regarding this new LTCC novel technology based in

recent system in package (SiP) developments [1].

LTCC based SiP approach offers a solution to the goal

of low cost, low power consumption and small size

due to its low loss at high frequencies and capability of

embedding passive components.

Band pass filter (BPF) is the most important

passive component in RF SiP for wireless LAN

systems. In this paper, the microstrip coupled line band

pass filter for 5GHz wireless LAN applications by

using 3D multilayered LTCC technology is

considered. This filter offers low insertion loss and

spurious free performance. The design and fabrication

procedure as well as the issues and solutions will be

discussed in detail. In this study, a 5GHz frequency

band with its high data rate of 54Mbps was selected

which are compatible with 802.11a WLAN application

as reported by [2] as shown in Table 1.0.

Table 1.0 : Wireless communication technologies for

WPAN and WLAN standards [2]

2. Theory

Transmission line resonator design structures

consist in of a combination of multi-lines of at least

one quarter guide wavelength. Using these structures,

filter components with different filtering characteristic

can be realized. Various design structures for

RF/microwave filters are available and the most

popular includes end-coupled, edge-coupled, inter

digital and hair-pin filters. Figure 1.0 show filters

designed with end-coupled, parallel-coupled, inter

digital , and hair-pin structures. Research activities

worldwide made so far in the design of wireless filters

using resonator design structures are reported in [3]

and [4]

Figure 1.0 : Example of BPF design structure a) end-

coupled, b)edge-coupled, c) Inter digital , and d) hairpin

lines

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This paper presents an edge-coupled BPF

using LTCC technology. Basically, a band pass filter is

a circuitry that provides transmission of frequencies

above and below a particular frequency range of ω1

and ω2 (pass band) of the filter, as well as attenuating

of other frequencies outside of this range [5]. This

characteristic can be represented by a graph shown in

Figure 2. ωc depicted in the figure is the centre

frequency of the filter, which is the middle point of the

frequency range of ω1 and ω2. The band pass filter is

crucial in signal transmissions as it selects/isolates a

specific signal of frequency bandwidth from input

signals that have a plurality of frequencies. It is also

effective in preventing external and internal

interference of signals, improving the signal-to-noise

ratio (SNR) that will consequently lead to effective

utilization of a frequency [6].

Figure 2 illustrating the basic curve of a band

3. Filter Design

The band pass filter circuit was realized

using microstrip coupled line. The design flow is

already discussed in elsewhere like [7] & [8].

According to [7], the basic design flow as shown in

Figure3.0.

Figure 3.0: Design flow for integrated RF/microwave

filters [8]

The desired physical design is of the parallel

coupled line type, as illustrated in Figure 3.0.

Therefore, the filter is to be constructed by cascading 5

parallel half-wave long resonators, open circuited at

both ends using Empire XCcel [9].These adjacent

resonators are then coupled along the length of quarter

wavelength at centre frequency as summarized in

equation (1).

l = λ/4…….. (1)

Figure 4.0 shows the dimensions of a parallel

coupled microstrip line.

Prior to drawing the layout of the desired microstrip

line band pass filter, design specifications are first to

be developed. These specifications indicate what to be

expected of the desired filter. Listed in Table 2 are the

design specifications to be designed:

Design Filter Specifications

Center Frequency, fo 5GHz

Lower and upper frequency cut-

off at 3dB

2GHz

Stop band attenuation at 7.5GHz >45dB

Passband ripple 0.1dB

Table 2 listing the microstrp coupled line band pass

filter’s spec

Meanwhile, the Figure 5.0 illustrates the expected

response curve is in fact a graph representation of table

1, which is the list of filter’s specifications.

Figure 4 illustrating the response curve expected of

filter based on design specifications.

The next principle step is to select the substrate

material. In this work, we used Ferro Tape as substrate

materal for design microstrip coupled line band pass

filter. The thickness (h) is 0.635 mm and dielectric

constant is (εr) 5.9. The properties of the Ferro tape

can be accessed in its manufacturing Data Sheet.

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The layout of the microstrip coupled line

band pass filter as shown in Figure 6.

Figure 6: Layout of 5GHz BPF

4. TMRND LTCC Process Flow

Figure 7.0 shows the Multilayer LTCC process flow

developed at TMRND’s LTCC laboratory which starts

from blanking until firing process.

Figure 7.0: Development of Multilayer LTCC at

TMRND

Figure 8.0 shows how the design of this band

pass filter was fabricated using multilayer LTCC

process at TMRND’s LTCC Laboratory. LTCC

process including the material selections, blanking,

punching, printing via screen printing, stacking,

laminating, firing and finally testing measurements.

Figure 8.0 : Fabrication & test measurement set-up for

BPF

RESULT AND DISCUSSION

The S-parameter simulation is performed to

obtain the response curve of the preliminary circuit

design as shown in Figure 9.0. The analysis of the

preliminary circuit can now be carried out by looking

at the simulated response curve as illustrated in Figure

10.

Figure 9 shows the final schematic circuit of band pass

filter configuration.

Figure 10 illustrates the S21 and S11 of the band pass

filter.

In figure 10, it can be seen that the required

bandwidth of 2 GHz of the lower and upper cut-off

frequency at 3dB is fulfilled (f2 – f1 = 2 GHz). While at

the same time referring to the design specifications

shown earlier in Figure 4, it is observed that the

measured bandwidth in Figure 10 is slightly shifted

forward by 5%. This percentage is however small, and

is adequate to meet the design requirements. The next

requirement to be fulfilled is for the attenuation to be

greater than 45 dB at 7.5 GHz. The measured response

suits incredibly close to the requirement, shifted

backward by only 1.1%. The centre frequency of 5

GHz also indicates a close-to-zero attenuation at 0.017

dB. Therefore, the measured response of the

preliminary circuit indicates that the circuit is to

perform reliably, and hence the circuit can now be

transformed into the physical layout.

Subsequent to the physical drawing of band

pass filter as illustrated earlier in Figure 4, the layout is

now simulated with S-parameters using EM simulation

EMPIRE XCcel. The resulting response of the S21

parameter, which represents the transmission

characteristics, is obtained as shown in Figure 11

498

Substrate Response S21

(dB)

VSW

R

BW fcenter

Measure -4.9 2.6 180

MHz

5.12

GHz

Ferro

A6M

Simulate -1.33 1.5 200

MHz

5.12

GHz

Figure 11 : Simulated and measured result of 5GHz

Band Pass filter.

The responses of the embedded filters were

measured using a network analyzer. As can be seen in

Figure 11, the measured S-parameters for the filter

embedded in LTCC exhibits a center frequency of

5.12GHz. a bandwidth of 200MHz and an insertion

loss of -4.9dB. Compared with simulated results, the

measured insertion loss is about 3.57dB lower than

that of the simulated values at center frequency,

fcenter equal to 5.12GHz. These measured results are

indeed not the most outstanding results expected of the

physical layout due to the shrinkage and variation of

dielectric constant after cofiring. In the LTCC tooling

design, the shrinkage published in the manufacture’s

datasheet resulting from LTCC tapes was utilized

instead of that obtained from a shrinkage test substrate

in the actual design.[10].

CONCLUSION

In conclusion, the development of LTCC

circuit can be significantly accelerated with the help of

electromagnetic analyses via CAD simulation. An

efficient design flow can be obtained when an

appropriate electromagnetic analysis method is used.

In this paper, the microstrip coupled line band pass

filter using LTCC technology is the solution to

applications in microwave filter circuits, as it makes

filter configurations of having maximum size

reductions possible. Plus, the traditional method of

transforming the lowpass prototype to a band pass

configuration is proven to be an efficient method to

finding the accurate preliminary circuit with

satisfactory response with the aim of achieving the

design goal with LTCC technology.

ACKNOWLEDGEMENT

The author would like to thank Telekom Malaysia

Berhad for financing this research work under project

RDTC/080700.

References

[1] Christopher M.Scanlan and Nozad karim, “System

in Packages technology, application and trends,”

SMTA International Proceedings, pp 764-773,2001

[2] M.Baba, S. Guttowski, H. Reichl, “An efficient

methodology for design and implementation of

embedded bandpass filters for RF/Wireless

applications,”9th International IEEE EPTC

Conference, Singapore, 1-12 Dec 2007.

[3] Gangqiang Wang, Minh Van, Fred Barlow and

Aicha Elshabini, “ An Interdigital Bandpass filter

embedded in LTCC for 5GHz Wireless LAN

Applications,”IEEE Microwave and wireless

components letters, May 2005.

[4] G.Prigent, E.Rius, F/le Pennec and S.Le Maguer,

“ A Design Method for improvement of λg/4

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Microwave and optical technology letters,

Oct 2003

[5] Bhatti R.A, “ Design and Analysis of a Parallel

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[6] Kung, F, Microstrip Filter Design, RF

Engineering – Passive Circuit, page 1-20,

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[7] M.Baba, S. Guttowski, H. Reichl, “A Design

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[8] Jens Muller, “ Design Connsiderations for Hybrid

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[9] http://www.empire.de,2007, IMST GmbH:

User and Reference Manual for the 3D EM Time

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[10] F. Tabatabai, H.S Al-Raweshidy, “ C and Ka-

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