Australian Journal of Basic and Applied Sciences, 7(6): 571-577, 2013 ISSN 1991-8178
Corresponding Author: Md. Rokunuzzaman, Institute of Space Science (ANGKASA) UniversitiKebangsaan Malaysia, 43600 UKM Bangi, Malaysia.
E-mail: robelhk@yahoo.com 571
Design of a Coupled-Line Bandpass Filter for Satellite Dish Antenna Receiver
1Md. Rokunuzzaman, 1M.T. Islam, 1R. Azim, 1Radial Anwar and 2Mhd Fairos Asillam
1Institute of Space Science (ANGKASA) UniversitiKebangsaan Malaysia, 43600 UKM Bangi,
Malaysia.
2National Space Agency of Malaysia.
Abstract: In this article a filter is proposed forreceiver antenna specification which communicates with the geostationary satellites transmitting television signals. Two-line coupled resonators of 4 stages are proposed for the filter. The designed filter has a bandpass response filtering frequencies from 10.2 GHz to 11.7 GHz. The filter is designed on Rogers RT/Duroid 5880 substrate with dielectric constant of 2.2 and a thickness of 0.762 mm. It is designed using Agilent Advanced Design System (ADS) Momentum software. At the pass band the filter gives an insertion loss of less than -2.5dB. The result found for the filter is by using 4 coupled lines in parallel with very simple design details. The average S11 at the passband is less than -13.145 dB. This filter specification can be used for filtering frequency ranging from 10.2 GHz to 11.7 GHz. The filter can be collaborated with other MMIC circuit designs. It is quite small compared to other coupled-line filters. The proposed filters dimension is 40 × 14.3 mm2. Key words: Bandpass • Coupled-line • Filter • Microwave frequency •Receiver •Satellite• television.
INTRODUCTION
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designed easily using Agilent Advanced Design System (ADS) software. For the ease of use ADS is selected as design tool. By using coupled line technology a frequency range from 10.2 GHz to 11.7 GHz is found.
Modeling of the Design:
The coupled-line filter is quite small compared to the coupled-line filters found nowadays. The proposed filter is designed by using Agilent Advanced Design System (ADS) software. After the design, the filter was simulated using Agilent ADS Momentum which simulates circuit based on Method of Moment (MOM).
Fig. 1: Coupled-line bandpass filter layout.
A Low Pass Prototype (LPP) is designed for designing the bandpass filter as an initial step. The steps for designing the prototype are given below: The Fractional Bandwidth (FBW) ∆ is given by:
From the butterworth LPP response table the values of g0, g1,g2, g3, g4 and g5 are found to get the desired attenuation. Then the calculations for the desired coupled-line bandpass filter are done by using equations given below:
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By using the odd and even mode impedance, the width, length and spacing between the coupled lines can be calculated. After finding a basic structure, it is optimized using the built in optimization tool of ADS Momentum.
Dimention of the Filter:
The filter ports are situated at the two corners of the coupled-line filter. The gap between the coupled-lines is stated 0.4 mm to have the result. 0.4 mm is large enough to achieve between microstrip coupled-lines with no error. If the gap between coupled-lines becomes smaller, better performance can be achieved with a drawback in design fabrication which is hard to achieve. As the gap between coupled-lines is fixed, the performance depends on the length and width of the coupled-lines. The width and length of the lines which are coupled are the same. The microstrip lines at the two corners of input and output ports widths and lengths are chosen to have better isolation at the rejecting band and better through at the desired band which is 10.2 GHz to 11.7 GHz.The design layout of the proposed filter is shown in Fig.1, where W1, W2, W3, W4, W5 and W6 show the width of polygons; L1, L2, L3, L4, L5 and L6 show the length of polygons; S3, S4, S5 and S6 show the gap between coupled-lines. They have the following values:
W1=4.25436 mm, L1=11.4463 mm, W2=0.8 mm, L2=5.3818368 mm, W3=1.614917 mm, L3=4.00352885 mm, W4=1.6329495 mm, L4=5.31807 mm, W5=0.431525 mm, L5=4.213648 mm, W6=3.5142 mm, L6=10.5296 mm,S3=0.4 mm, S4=0.4 mm, S5=0.4 mm, S6=0.4 mm.
RESULTS AND DISCUSSION
The performance of the proposed filter is analyzed using the Agilent Advanced Design Systems (ADS) Electromagnetic Simulator Momentum which simulates planar circuits using Method of Moment (MOM).
(a)
(b)
(c)
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(b)
(c)
Fig. 3: Phase of S-parameters for (a) S11, (b) S21 and (c) S22.
In Figure 2 (a), for the S11, a bandwidth from 10.2 GHz to 11.7 GHz is found to have magnitude response of less than -13.145dB. Figure 2 (b) shows the S21 response of the filter. S21 has a value above -3 dB within the frequency from 10.2 GHz to 11.85 GHz. Figure 2(c) shows the S-parameter response of port 2. S22 gives a bandwidth from 10.2 GHz to 11.7 GHz with a magnitude of less than-12.605 dB.
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m1:
Freq=10.2 GHz; S(1,1)=0.304/-25.787 Impedance=83.301-j24.3 Ω
m2:
Freq=11.7 GHz; S(1,1)=0.145/67.069 Impedance=53.905+j14.696 Ω
(c) m3:
Freq=10.2 GHz; S(2,2)=0.337/123.444 Impedance=29.868+j18.923 Ω m2:
Freq=11.7 GHz; S(2,2)=0.220/-26.366 Impedance=72.737-j14.938 Ω
(b) m5:
Freq=11.8 GHz; S(2,1)=0.842/81.237 Impedance=10.052+j57.289 Ω m6:
Freq=10.2 GHz; S(2,1)=0.720/92.982
Impedance=15.106+j45.130 Ω
Fig. 4: Impedance response characterization in smith chart for (a) S11 (b) S21 and (c) S22 Conclusion:
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ACKNOWLEDGEMENT
The authors would like thank Institute of Space Science (ANGKASA), UniversitiKebangsaan Malaysia and Ministry of Science Technology and Innovation, Malaysia, science fund no.: 01-01-02-SF0608 for sponsoring this work.
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