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Modification in microstrip low pass filter using bulb shape patch
Int. J. Electron. Commun. (AEÜ) 63 (2009) 1076 – 1079 www.elsevier.de/aeue
LETTER
Modification in microstrip low pass filter using bulb shape patch Kumud Ranjan Jha∗ , Manish Rai School of Electronics and Communication Engineering, Shri Mata Vaishno Devi University, Katra, Jammu and Kashmir, India Received 16 May 2008; accepted 21 August 2008
Abstract This paper presents bulb type semicircular microstrip low pass filter with the sharp rejection and wide stop band. The proposed design is based on the calculation of parameters from traditional high–low impedance method and is available in the literature of microstrip filter. To further improve the design performance, high impedance lines are magnetically coupled, resulting an attenuation pole near −3 dB cut off point of the filter. This design gives insight in designing a low pass filter with reduced size with an arbitrary geographical shape. 䉷 2008 Elsevier GmbH. All rights reserved. Keywords: Microstrip low pass filter; High–low impedance; Bulb type microstrip filter
1. Introduction Due to increasing constraint of reduction in size with optimum performance, design of many low pass filters are available in the literature with different methods. The conventional filter design method is normally not used nowadays due to inherited deficiencies like slow roll off in the stop band, poor frequency response in the pass band, narrow stop band [1,2]. A number of methods are available in literature to design the low pass filter with the suitably selection of stub. A filter has been designed using hairpin resonator [3], which requires lot of calculations using transmission parameters. DGS and PBG filters using high–low impedance techniques have also been designed but these do not give a way to reduce size of filters [4–7]. Filters using inter digital capacitances based on even and odd mode analysis are also reported. Performances of this kind of filters are compatible with modern filter requirements [8], but needs extraction of capacitance, which is a cumbersome task. ∗ Corresponding author.
E-mail address: [email protected] (K.R. Jha). 1434-8411/$ - see front matter 䉷 2008 Elsevier GmbH. All rights reserved. doi:10.1016/j.aeue.2008.08.007
A simple microstrip low pass filter is proposed in [9], but it lacks sufficient return loss in pass band. A skirt type filter based on even and odd modes is also described where a rectangular stub has been selected for realization. Here, a new filter using bulb type semicircular capacitive patch is proposed with reduced total effective area and the improved performance as compared to filter used in [10].
2. Design analysis A 3rd order Chebyshev filter is considered for designing purpose. Method of analysis begins with the calculation of inductive and capacitive stubs with the help of traditional high–low filter design [11]. Even though filter realization using [11] shows a reduction in elements’ size, circuit shows a poor response. The technique reported in [10] improves the performance of the filter. However, size of the filter and performance can be further improved if the capacitive stub is modeled as the parallel capacitances C = CP + Cf
(1)
K.R. Jha, M. Rai / Int. J. Electron. Commun. (AEÜ) 63 (2009) 1076 – 1079
1077
where C is the total capacitance extracted from the design table. CP is the parallel plate capacitance between metallic plate and ground plate and Cf is the fringing field capacitance associated with electric field lines passing through air via dielectric to the ground. Since parallel plate capacitance is directly proportional to the surface area, geometry of the plate may be changed while keeping CP constant. With this logic, filter can be realized with the help of any kind of geometry.
3. Existing filters design A 3rd order Chebyshev filter with −3 dB cut off frequency at 2 GHz and attenuation of 0.1 dB in pass band with port impedance 50 is analyzed using the substrate of dielectric constant 3.2, thickness 0.762 mm. Prototype and real values of inductances and capacitance are calculated using [11].
Fig. 2. Response of skirt filter.
3.1. Conventional microstrip low-pass filter Prototype values of inductance and capacitance are converted in to the microstrip structure using existing technique. A number of iterations are made to reduce parasitic components and this filter requires 134.21 mm2 effective area on the substrate. This kind of filter is not suitable for the modern communication system due to very poor stop band characteristic and wide effective are on the substrate.
Total effective area of this filter is 87.02 mm2 and single attenuation pole occurs at the frequency 3.85 GHz. Although along with sharp cut off frequency and wide stop band, the filter shows a reduction of 35.11% of area as compared to conventional filter, yet there is a possibility of further reduction in the size by using arbitrary shape of the capacitive patch and folding the high impedance lines.
3.2. Skirt type low pass filter
4. Proposed bulb type microstrip low pass filter
Here filter is designed using even and odd mode analysis [10]. Response of the filter is compatible with the modern communication system. The value of inductance and capacitance are also extractable from the conventional filter design technique. Resulting structure using the conventional filter design technique and its simulated response are shown in Figs. 1 and 2, respectively.
Here filter analysis has been done with the help of the classical filter design technique with the added feature of magnetic coupling as discussed earlier. The capacitive rectangular stub is replaced by a bulb type patch with area of 39.90 mm2 as shown in Fig. 3. The proposed filter shows multiple attenuation poles in the stop band. To investigate the exact cause of generation of multiple attenuation pole in the stop band as shown in Fig. 4, the structure is simulated for different value of ‘s’ while keeping the total length of high impedance lines constant. For low value of ‘s’ attenuation poles are generated due to the coupling between parallel high impedance lines, bending of impedance lines and coupling between left upper edge of capacitive stub and right side high impedance line. The first attenuation pole near cut off frequency is due to coupling between parallel high impedance lines whereas the third attenuation pole is due to the discontinuity at the right angle bend of high impedance lines. The Middle attenuation pole is generated by coupling between high and low impedance lines. When the value of ‘s’ is less, the coupling between right side high impedance line and capacitive patch is experienced and for extreme high value ‘s’ the coupling is between high impedance lines and feed lines. When’s’ is
Fig. 1. Skirt microstrip low pass filter feed line width w1 = 1.8, w2 = 0.32, l = 6.78, b = 5.76, h = 6.94, g = 0.55 (dimensions in mm).
1078
K.R. Jha, M. Rai / Int. J. Electron. Commun. (AEÜ) 63 (2009) 1076 – 1079
Table 1. Simulated result Filter structures
Capacitive patch area (in mm2 )
Effective area on substrate (in mm2 )
Conventional low pass filter Skirt type low pass filter Bulb type low pass filter
39.97 39.97 39.90
134.21 87.02 77.43
5. Results and conclusions
Fig. 3. Bulb type microstrip low pass feed line width w1 = 1.8, w2 = 0.32, l1 = 5.37, l2 = 2.46, l3 = 4.13, g1 = 0.55, g2 = 0.64, g3 = 0.70, d = 8.05, s = 0.277 (dimensions in mm).
Results are summarized in Table 1. It is observed from the above table that proposed filter design requires 77.43 mm2 effective area, giving an 11.49% improvement over existing skirt filter area. First attenuation pole −65.2 dB at 4.0 GHz is achieved in the proposed design. Simulated results by two different software as shown in Fig. 4, are in the close agreement in the pass band of the filter. A deviation in the results is observed in the stop band due to different simulation technology involved in software. Simulated result by Sonnet Lite shows instable S21 from 10 to 12 GHz, which is due to the effect of box resonance. In the present letter a new structure of microstrip low pass filter has been analyzed and results have been verified. This technique may be extended to miniaturise the other capacitive structure topology by making the trade off between separation parameter ‘s’ and total effective area.
References
Fig. 4. Response of proposed filter.
approximately half of the length of high impedance line, the middle attenuation pole disappears. In the present design s = 0.277 mm is selected to improve the stop band characteristics and reduce the effective area of proposed filter. To validate the results the proposed structure is simulated using two softwares (a) Sonnet Lite [12] and (b) IE3D [13]. The results of simulation are shown in Fig. 4. The response in Fig. 4 shows −3.02 dB cut off frequency at 2.01 GHz, First attenuation pole at 4.1 GHz, second attenuation pole at approximately 6.5 GHz and third attenuation pole approximately at 9.0 GHz. The stop band rejection is better than −20 dB from 3.5 to 10 GHz approximately.
[1] Hong JS, Lancaster MJ. Microstrip filters for RF/microwave applications. New York: Wiley; 2001. [2] Lee MQ, Ryu KK. Novel low pass filter for broad band spurious suppression. IEEE MTT-S Digest; 2002. [3] Hsies LH, Chang K. Compact elliptic-function low-pass filters using microstrip steapd-impedance hairpin resonators. IEEE MTT 2003;51(1):193–9. [4] Ahn D, Park JS, Kim CS, Kim J, Qian Y, Itoh T. A design of the low-pass filter using the novel microstrip defected ground structure. IEEE Trans Microwave Theory Tech 2001;49: 86–92. [5] Cho YB, Jum KS, Kim IS. Small sized quasi eleptic function microstrip low pass filter based on defected ground structure and open stubs. Microwave Journals, 2004. [6] Adel B, Rahman A, Verma AK, Boutejdar A, Omar AS. Control of band stop response of hi-lo microstrip low pass filter using slot in ground plane. IEEE MTT 2004;52(3): 1008–13. [7] Rumsey I, May MP, Kelly PK. Photonic bandgap structure used as filters in microstrip circuits. IEEE Microwave Guided Wave Lett 1998;8(10):336–8. [8] Tu WH, Chang K. Compact microstrip low-pass filter with sharp rejection. IEEE Microwave Wireless Components Lett 2005;15(6). [9] Kuo JT, Shen J. A compact distributed low-pass filter with wide stop band. IEEE Proceeding of APMC 2001, Taipei, Taiwan, ROC. p. 330–2.
K.R. Jha, M. Rai / Int. J. Electron. Commun. (AEÜ) 63 (2009) 1076 – 1079
[10] Li R, Kim DI. New compact low-pass filter with board stopband and sharp skirt characteristics, APMC 2005 proceedings. [11] Fooks EH, Jakarevicius RA. Microwave engineering using microstrip circuits. Prentice-Hall of Australia; 1990 p. 167–9. [12] Sonnet Lite ver.11.55. [13] Zeland IE3D Software ver. 14.16. Kumud Ranjan Jha born in 1973 passed AMIE(I) examination in 1999 and Master of Engineering from Birla Institute of Technology, Mesra, Ranchi Jharkhand,(India) in 2006. Presently he is Assistant Professor in the School of Electronics and Communication Engineering, Shri Mata Vaishno Devi University, Katra, Jammu and Kashmir, India. His area of research is Microwave/RF component design.
1079
Manish Rai born in 1968 passed B.Tech and M.Tech examination from Allahabad University, India and completed PhD in 2006 from MNIT Allahabad. Presently he Associate Professor in the School of Electronics and Communication Engineering, Shri Mata Vaishno Devi University, Katra, Jammu and Kashmir India.
LETTER
Modification in microstrip low pass filter using bulb shape patch Kumud Ranjan Jha∗ , Manish Rai School of Electronics and Communication Engineering, Shri Mata Vaishno Devi University, Katra, Jammu and Kashmir, India Received 16 May 2008; accepted 21 August 2008
Abstract This paper presents bulb type semicircular microstrip low pass filter with the sharp rejection and wide stop band. The proposed design is based on the calculation of parameters from traditional high–low impedance method and is available in the literature of microstrip filter. To further improve the design performance, high impedance lines are magnetically coupled, resulting an attenuation pole near −3 dB cut off point of the filter. This design gives insight in designing a low pass filter with reduced size with an arbitrary geographical shape. 䉷 2008 Elsevier GmbH. All rights reserved. Keywords: Microstrip low pass filter; High–low impedance; Bulb type microstrip filter
1. Introduction Due to increasing constraint of reduction in size with optimum performance, design of many low pass filters are available in the literature with different methods. The conventional filter design method is normally not used nowadays due to inherited deficiencies like slow roll off in the stop band, poor frequency response in the pass band, narrow stop band [1,2]. A number of methods are available in literature to design the low pass filter with the suitably selection of stub. A filter has been designed using hairpin resonator [3], which requires lot of calculations using transmission parameters. DGS and PBG filters using high–low impedance techniques have also been designed but these do not give a way to reduce size of filters [4–7]. Filters using inter digital capacitances based on even and odd mode analysis are also reported. Performances of this kind of filters are compatible with modern filter requirements [8], but needs extraction of capacitance, which is a cumbersome task. ∗ Corresponding author.
E-mail address: [email protected] (K.R. Jha). 1434-8411/$ - see front matter 䉷 2008 Elsevier GmbH. All rights reserved. doi:10.1016/j.aeue.2008.08.007
A simple microstrip low pass filter is proposed in [9], but it lacks sufficient return loss in pass band. A skirt type filter based on even and odd modes is also described where a rectangular stub has been selected for realization. Here, a new filter using bulb type semicircular capacitive patch is proposed with reduced total effective area and the improved performance as compared to filter used in [10].
2. Design analysis A 3rd order Chebyshev filter is considered for designing purpose. Method of analysis begins with the calculation of inductive and capacitive stubs with the help of traditional high–low filter design [11]. Even though filter realization using [11] shows a reduction in elements’ size, circuit shows a poor response. The technique reported in [10] improves the performance of the filter. However, size of the filter and performance can be further improved if the capacitive stub is modeled as the parallel capacitances C = CP + Cf
(1)
K.R. Jha, M. Rai / Int. J. Electron. Commun. (AEÜ) 63 (2009) 1076 – 1079
1077
where C is the total capacitance extracted from the design table. CP is the parallel plate capacitance between metallic plate and ground plate and Cf is the fringing field capacitance associated with electric field lines passing through air via dielectric to the ground. Since parallel plate capacitance is directly proportional to the surface area, geometry of the plate may be changed while keeping CP constant. With this logic, filter can be realized with the help of any kind of geometry.
3. Existing filters design A 3rd order Chebyshev filter with −3 dB cut off frequency at 2 GHz and attenuation of 0.1 dB in pass band with port impedance 50 is analyzed using the substrate of dielectric constant 3.2, thickness 0.762 mm. Prototype and real values of inductances and capacitance are calculated using [11].
Fig. 2. Response of skirt filter.
3.1. Conventional microstrip low-pass filter Prototype values of inductance and capacitance are converted in to the microstrip structure using existing technique. A number of iterations are made to reduce parasitic components and this filter requires 134.21 mm2 effective area on the substrate. This kind of filter is not suitable for the modern communication system due to very poor stop band characteristic and wide effective are on the substrate.
Total effective area of this filter is 87.02 mm2 and single attenuation pole occurs at the frequency 3.85 GHz. Although along with sharp cut off frequency and wide stop band, the filter shows a reduction of 35.11% of area as compared to conventional filter, yet there is a possibility of further reduction in the size by using arbitrary shape of the capacitive patch and folding the high impedance lines.
3.2. Skirt type low pass filter
4. Proposed bulb type microstrip low pass filter
Here filter is designed using even and odd mode analysis [10]. Response of the filter is compatible with the modern communication system. The value of inductance and capacitance are also extractable from the conventional filter design technique. Resulting structure using the conventional filter design technique and its simulated response are shown in Figs. 1 and 2, respectively.
Here filter analysis has been done with the help of the classical filter design technique with the added feature of magnetic coupling as discussed earlier. The capacitive rectangular stub is replaced by a bulb type patch with area of 39.90 mm2 as shown in Fig. 3. The proposed filter shows multiple attenuation poles in the stop band. To investigate the exact cause of generation of multiple attenuation pole in the stop band as shown in Fig. 4, the structure is simulated for different value of ‘s’ while keeping the total length of high impedance lines constant. For low value of ‘s’ attenuation poles are generated due to the coupling between parallel high impedance lines, bending of impedance lines and coupling between left upper edge of capacitive stub and right side high impedance line. The first attenuation pole near cut off frequency is due to coupling between parallel high impedance lines whereas the third attenuation pole is due to the discontinuity at the right angle bend of high impedance lines. The Middle attenuation pole is generated by coupling between high and low impedance lines. When the value of ‘s’ is less, the coupling between right side high impedance line and capacitive patch is experienced and for extreme high value ‘s’ the coupling is between high impedance lines and feed lines. When’s’ is
Fig. 1. Skirt microstrip low pass filter feed line width w1 = 1.8, w2 = 0.32, l = 6.78, b = 5.76, h = 6.94, g = 0.55 (dimensions in mm).
1078
K.R. Jha, M. Rai / Int. J. Electron. Commun. (AEÜ) 63 (2009) 1076 – 1079
Table 1. Simulated result Filter structures
Capacitive patch area (in mm2 )
Effective area on substrate (in mm2 )
Conventional low pass filter Skirt type low pass filter Bulb type low pass filter
39.97 39.97 39.90
134.21 87.02 77.43
5. Results and conclusions
Fig. 3. Bulb type microstrip low pass feed line width w1 = 1.8, w2 = 0.32, l1 = 5.37, l2 = 2.46, l3 = 4.13, g1 = 0.55, g2 = 0.64, g3 = 0.70, d = 8.05, s = 0.277 (dimensions in mm).
Results are summarized in Table 1. It is observed from the above table that proposed filter design requires 77.43 mm2 effective area, giving an 11.49% improvement over existing skirt filter area. First attenuation pole −65.2 dB at 4.0 GHz is achieved in the proposed design. Simulated results by two different software as shown in Fig. 4, are in the close agreement in the pass band of the filter. A deviation in the results is observed in the stop band due to different simulation technology involved in software. Simulated result by Sonnet Lite shows instable S21 from 10 to 12 GHz, which is due to the effect of box resonance. In the present letter a new structure of microstrip low pass filter has been analyzed and results have been verified. This technique may be extended to miniaturise the other capacitive structure topology by making the trade off between separation parameter ‘s’ and total effective area.
References
Fig. 4. Response of proposed filter.
approximately half of the length of high impedance line, the middle attenuation pole disappears. In the present design s = 0.277 mm is selected to improve the stop band characteristics and reduce the effective area of proposed filter. To validate the results the proposed structure is simulated using two softwares (a) Sonnet Lite [12] and (b) IE3D [13]. The results of simulation are shown in Fig. 4. The response in Fig. 4 shows −3.02 dB cut off frequency at 2.01 GHz, First attenuation pole at 4.1 GHz, second attenuation pole at approximately 6.5 GHz and third attenuation pole approximately at 9.0 GHz. The stop band rejection is better than −20 dB from 3.5 to 10 GHz approximately.
[1] Hong JS, Lancaster MJ. Microstrip filters for RF/microwave applications. New York: Wiley; 2001. [2] Lee MQ, Ryu KK. Novel low pass filter for broad band spurious suppression. IEEE MTT-S Digest; 2002. [3] Hsies LH, Chang K. Compact elliptic-function low-pass filters using microstrip steapd-impedance hairpin resonators. IEEE MTT 2003;51(1):193–9. [4] Ahn D, Park JS, Kim CS, Kim J, Qian Y, Itoh T. A design of the low-pass filter using the novel microstrip defected ground structure. IEEE Trans Microwave Theory Tech 2001;49: 86–92. [5] Cho YB, Jum KS, Kim IS. Small sized quasi eleptic function microstrip low pass filter based on defected ground structure and open stubs. Microwave Journals, 2004. [6] Adel B, Rahman A, Verma AK, Boutejdar A, Omar AS. Control of band stop response of hi-lo microstrip low pass filter using slot in ground plane. IEEE MTT 2004;52(3): 1008–13. [7] Rumsey I, May MP, Kelly PK. Photonic bandgap structure used as filters in microstrip circuits. IEEE Microwave Guided Wave Lett 1998;8(10):336–8. [8] Tu WH, Chang K. Compact microstrip low-pass filter with sharp rejection. IEEE Microwave Wireless Components Lett 2005;15(6). [9] Kuo JT, Shen J. A compact distributed low-pass filter with wide stop band. IEEE Proceeding of APMC 2001, Taipei, Taiwan, ROC. p. 330–2.
K.R. Jha, M. Rai / Int. J. Electron. Commun. (AEÜ) 63 (2009) 1076 – 1079
[10] Li R, Kim DI. New compact low-pass filter with board stopband and sharp skirt characteristics, APMC 2005 proceedings. [11] Fooks EH, Jakarevicius RA. Microwave engineering using microstrip circuits. Prentice-Hall of Australia; 1990 p. 167–9. [12] Sonnet Lite ver.11.55. [13] Zeland IE3D Software ver. 14.16. Kumud Ranjan Jha born in 1973 passed AMIE(I) examination in 1999 and Master of Engineering from Birla Institute of Technology, Mesra, Ranchi Jharkhand,(India) in 2006. Presently he is Assistant Professor in the School of Electronics and Communication Engineering, Shri Mata Vaishno Devi University, Katra, Jammu and Kashmir, India. His area of research is Microwave/RF component design.
1079
Manish Rai born in 1968 passed B.Tech and M.Tech examination from Allahabad University, India and completed PhD in 2006 from MNIT Allahabad. Presently he Associate Professor in the School of Electronics and Communication Engineering, Shri Mata Vaishno Devi University, Katra, Jammu and Kashmir India.