Available online at www.sciencedirect.com
ScienceDirect Procedia Computer Science 86 (2016) 7 – 10
2016 International Electrical Engineering Congress, iEECON2016, 2-4 March 2016, Chiang Mai, Thailand
Design of Bandpass Filter Based on Asymmetrical T-shaped Resonators Reungyot Lerdwanittipa,* ApiradaNamsanga and Phakkawat Jantreeb b
a Avionics Division, Civil Aviation Training Center joined with Suranaree University of Technology, Bangkok, 10900, Thailand Faculty of Engineering and Architecture, Rajamangala University of Technology Suvarnabhumi, Yanyau, Suphanburie, 72130, Thailand
Abstract Two different T-shared resonators are used for the proposed bandpass filter with wide rejection band. Each resonator is considered with dissimilar impedance and electrical length because of the harmonics resonant response generating with difference positions. All theoretical and experimental results are verifying this concept at the fundamental frequency 2.45 GHz. The insertion loss is 2.74 dB and the return loss is 21.95 dB respectively. The levels of stopband are lower than 25 dB up to 20 GHz. © 2016 2016The TheAuthors. Authors. Published Elsevier Published by by Elsevier B.V.B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Organizing Committee of iEECON2016. Peer-review under responsibility of the Organizing Committee of iEECON2016 Keywords: bandpass filter; T-shaped resonator; harmonic suppression; hook feed line
1. Introduction A novel compact microwave bandpass filter with high selectivity, wide stopband and small insertion loss is a good performance demanding in front end of wireless local area network [1]. There are a lot of resonator structures for proposing bandpass filter. A T-shaped resonator is one of favorite structures to be used. A dual-band bandpass filter using folded T-shaped half-wavelength resonator is proposed in [2].With capacitive load coupling for feeding and multiple transmission zeros are generated, although not good for the second band bandwidth is produced.The authors in [3] presented the technique to obtain extremely sharp skirt by using T-shaped resonators combine with
* Corresponding author. Tel.: +6-681-665-5315; fax: +6-622-726-104. E-mail address:
[email protected].
1877-0509 © 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Organizing Committee of iEECON2016 doi:10.1016/j.procs.2016.05.002
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high and low-impedance lossless line lowpass and U-shaped suppressing cells.On the other hand, defected ground structure (DGS) is applied to etch a microstrip line ground has a main advantage for providing high capacitive coupling [5]. In this paper, the bandpass filter with difference asymmetrical T-shaped resonators and hook feed-lines are proposed as the fundamental concept which issimilar to [6] but improved the internal coupling by folded T-shaped resonator. With the asymmetrical structures, the wide rejection band is observed. To validate the results, a proposed bandpass filter is designed and fabricated.
2. Design T-shaped structure resonator is selected to design the presented bandpass filter with wide harmonics suppression because it is a modified of step-impedance resonator (SIR) so that it is flexible to adjust the harmonics response shifting. As present in [6], the resonant equation is analyzed from the impedance and electrical length structures are shown in Fig 1(a), which is composed of equation (1) and equation (2). .
Zx
Z1Z 2 cot T1 cot T2 Z1 cot T1 Z 2 cot T2
(1)
Z3 Z4 Z4 Z x tan T3 Z3Z x tan T4 Z32 tan T3 tan T4
0
(2)
The different T-shaped resonators are intended and also produced in different frequency response as shown in Fig.1(b). It is noticed that the both resonators generated the same fundamental frequency of 2.45 GHz, which are calculated from equation (2), but they produced in different of harmonics frequencies so that they could eliminate the unwanted signals by themselves as shown in Fig.1(b).
(a)
(b)
80
80
70
70
T1 = T2 = 100
60
60
T1 = T2 = 120
50
50
T1 = T2 = 140
40
40
T4
T4
Fig. 1. (a) Basic structure of T-shaped resonator (b) The frequency responses of two T-shaped resonators
30
T1 = T2 = 20
20
T1 = T2 = 35
10 0 10
30 20 10
T1 = T2 = 50
20
30
0 40
50
T3 (a)
60
70
80
0
10
20
30
40
50
T3
(b)
Fig. 2. The calculated electrical length of T3 versus T4 (a) the first resonator (b) the second resonator
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Fig.2(a) shows the relationship between T3 and T4 of the first resonator when fixed the value of the impedance Z1 = Z2= 85 Ω, Z3 = 100 Ω and Z4 = 25 Ω and then changing T1 equal T2 of 20°, 35°and 50°, respectively. In same method, the second resonator is designed with the relationship response as shown in Fig.2(b). It is plotted with the impedance Z1 = Z2 = 70 Ω, Z3 = 60Ω and Z4 = 25Ω and changed the electrical length T1 equal T2 at 100°, 120°, 140°, respectively. To fabricate the proposed bandpass filter, the PCB of ARON 25N with the relative dielectric constant of 3.38, the loss tangent of 0.002, and the thickness of 0.8 mm is used for WLAN system design at 2.45 GHz. Input and Output port are the hook feed line structure with the standard impedance 50 Ω. Finally, the T-shaped resonators have been achieved for high performance, resulting of the first resonator as: Z1= 84.52Ω, Z2 = 84.52Ω, Z3 = 97.59Ω, and Z4 = 27.65Ω, corresponding to their electrical lengths of T1 = 34.94°, T2 = 34.94°, T3 = 49.02° and T4 =30.60°, respectively which is relating in Fig.2(a). Similarly referring to Fig.2(b), the impedances of second resonator are Z1= 71.10Ω, Z2 = 71.10Ω, Z3 = 61.70Ω, and Z4 = 25.81Ω and their electrical lengths of T1 = 122.12°, T2 = 122.12°, T3 = 11.33° and T4 = 37.21°, respectively. The set of dimension parameters as shown in Fig. 3(a) which is simulated of electromagnetic software is given as following: W1 = 4.7 mm, W2 = 1.3 mm, W3 = 1 mm, W4 = 0.78 mm, W5 = 1.2 mm, L1 = 6.3 mm, L2 = 9.18 mm, L3 = 1.69 mm, L4 = 2.39 mm, L5 = 2.3 mm, L6 = 8.07 mm, L7 = 3.1 mm, L8 = 7.17 mm, L9 = 8 mm, L10 = 6.93 mm, L11 = 5.15 mm, L12 = 3.5 mm, L13 = 4.7 mm, G1 = 0.2 mm, G2 = 0.2 mm, G3 = 0.45 mm. To confirm the simulated results, the E5071C ENA network analyzer is used to for measuring the insertion loss (S21) and the return loss (S11) of the fabricated filter. Fig. 4 displays the comparisons between the measured and simulated performances of the fabricated bandpass filter. At the center frequency 2.45 GHz, The insertion loss is 2.74 dB and the return loss is 21.95 dB. Among them, the Relative Stop-band Bandwidth (RSB) is calculated by:
RSB
stopband bandwidth stopband center
(3)
The rejection band of the proposed filter is referred to 20 dB suppression, so that the corresponding RSB is defined as 2 which is higher than the previous works. The highest rejection is not only involving asymmetrical T-shaped resonators which are generated in different frequency response, but also suppressed from the hook feed-lines which are published in [6].
L7 G2 L6 L10
L9
W5 L11
L13 L12
G1
L3
G3
L4 W4
L5
W1
W2
L1
L2
L8
W3
Fig. 3. The proposed bandpass filter (inset) and its circuit configuration
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Fig. 4.The Insertion loss and the return loss of the proposed bandpass filter
3. Conclusion In this paper, the T-shaped resonator bandpass filter can be suppressed for wide stopband attenuation more than 25 dB until 8f0. The proposed filter dimension is 29.13 × 21.90 mm2. The simulation and measurement are compatible as well and better than the previous work. The advantage of asymmetrical resonators and hook feedline structure are the simple method to eliminate the unwanted signal and easy to fabricate, compact and low cost for applied to communication system
Acknowledgements The authors would like to thank Asst. Prof. Dr.Pongsathorn Chomtong and Asst. Prof. Dr.Chatree Mahatthanajatuphat for kindly recommendations.
References 1. J. S. Hong and M. J. Lancaster, Microwave filters for RF/microwave application. John Wiley & Sons, Inc., 2001. 2. B. F. Zong, G. M. Wang, H. Y. Zeng and Y. W. Wang, Compact and High Performance Dual-band Bandpass Filter using Resonatorembedded Scheme for WLANs.Radio engineering Academic Journal, vol. 21, Issue 4, p. 1050-1053, Dec. 2012. 3. M. Hookari and G. Karimi, Design of Microstrip Filter Using Modified T-shaped with Wide Stopband. International Journal of Engineering & Technology Sciences (IJETS) 2 (2), p. 138-145, March 2014. 4. S. Amiri, N. Khajavi and M. Khajavi, Design of Compact RF Filters with Narrow Band-Pass and Wide Stop-Band by Open-Stub & T-shaped Microstrip Resonators and Defected Ground Structure (DGS). 2014 International Conference on Communications, Signal Processing and Computers, p.198-201, Switzerland, Feb. 22-24, 2014. 5. X. Guan, W. Fu, H. Liu, D. Ahn and J.-S. Lim, A Novel Dual-Mode Bandpass Filter Based on a Defected Waveguide Resonator. ETRI Journal, vol. 33, no. 6, Dec. 2011. 6. R.Lerdwanittip, A.Namsang, and P. Akkaraekthalin, Bandpass Filters using T-shape Stepped ImpedanceResonators for Wide Harmonics Suppression and theirApplication for a Diplexer. Journal of Semiconductor Technology and Science, vol.11, no.1, March, 2011.
