DESIGN AND SIMULATION OF A MICROSTRIP BAND PASS FILTER FOR GPS AND BLUETOOTH APPLICATIONS Girraj Sharma 2, Himanshu Joshi ,Yash Walia
[email protected]
Abstract - This paper presents a practical design procedure for Microstrip bandpass filters using ADS and sonnet. The design process starts with the theoretical design of the filter. Finally, the results of the implementation of the design are presented. the sonnet simulation gave a center frequency of 1.9 GHz. This filter is suitable for GSM,GPS and bluetooth applications I. INTRODUCTION Band pass filters are essential part of any signal processing or communication systems, the integral part of superhetrodyne receivers which are currently employed in many RF/Microwave communication systems. At Microwave Frequencies the discrete components are replaced by transmission lines, for low power applications microstrip are used which provide cheaper and smaller solution of Band Pass Filter. This Paper describes about the design of the microwave Bandpass filter by using microstrip technology. There are many possible techniques used to create microstrip filters A fifth order chebyshev microstrip filter is designed . II. BASIC THEORY PARALLEL-COUPLED,HALF-WAVELENGTH RESONATORS FILTERS
Figure 2.1 illustrates a general structure of parallel-coupled (or edge-coupled); microstrip bandpass filters that use halfwavelength line resonators. They are positioned so that adjacent resonators are parallel to each other along half of their length. This parallel arrangement gives relatively large coupling for a given spacing between resonators, and thus, this filter structure is particularly convenient for constructing filters having a wider bandwidth as compared to the structure for the end-coupled microstrip filters.
The design equations for this type of filter are given by
J 01 FBW Y0 2 g 0 g1
J j , j 1 Y0
FBW
1
2
g j g j 1
J n,n1 Y0
(1a) for j=1 to n-1
FBW 2 g n g n1
(1b)
`
(1c)
where g0, g1… gn are the element of a ladder-type low-pass prototype with a Normalized cutoff Ωc = 1, and FBW is the fractional bandwidth of band-pass filter. J j, j+1 are the characteristic admittances of J-inverters and Y0 is the characteristic admittance of the terminating lines. The equation above will be use in end-coupled line filter because the both types of filter can have the same low-pass network representation. However, the implementation will be different. To realize the J-inverters obtained above, the even- and oddmode characteristic impedances of the coupled microstrip line resonators are determined by
( Z 0e ) j , j 1
J J 1 [1 j , j 1 ( j , j 1 ) 2 ] Y0 Y0 Y0
for j=0 to n
( Z 0o ) j , j 1
(2a)
J J 1 [1 j , j 1 ( j , j 1 ) 2 ] Y0 Y0 Y0
for j=0 to n
(2b) III. DESIGN METHODOLOGY
Figure 2.1: General structure of parallel (edge)-coupled microstrip bandpass
A microstrip hairpin bandpass filter is designed to have a fractional bandwidth 20% or FBW = 0.2 at a midband frequency f0 = 1.9 GHz.A fivepole (n=5) Chebyshev lowpass prototype with a passband ripple of 0.1 dB is chosen. The lowpass prototype parameters, given for a normalized lowpass cutoff frequency Ωc = 1, are g0 = g6 = 1.0, g1 = g5 = 1.7058, g2 = g4 = 1.2296, and g3 = 2.5408
filter.
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The next step of the filter design is to find the dimensions of coupled microstrip lines that exhibit the desired even- and oddmode impedances. Firstly, determine equivalent single microstrip shape ratios (w/d) s. Then it can relate coupled line ratios to single line ratios. For a single microstrip line,
Z ose Z oso
g
o 300 mm re f (GHz ) re
Thus the required resonator,
g 4
c 4 f re
Using the design equations for coupled microstrip lines given (3a) and (3b), the width and spacing for each sections are found.
( Z oe ) j , j 1 2 ( Z oo ) j , j 1 2
Use single line equations to find (w/h)se and (w/h)so from Zose and Zoso. With the given r =4.2, find that for Zo=50, w/h is approximately 1.95. Therefore, W/h 2 has been chosen for this case. W For 2 h
The layout of the final filter designwith all the determined dimensions is illustrated in Figure 3.1. The filter is with a substrate size of 140 by 30 mm. The input and output resonators are slightly shortened to compensate for the effect of the tapping line and the adjacent coupled resonator. The EM simulated performance of the filter is shown in Figure 4.1 . Table I Required parameters value of microstrip line.
W 8 exp( A) h exp( 2 A) 2
Z0e (ohms) Z0o (ohms)
with
Z c r 1 r 1 0.11 0.23 60 2 r 1 r 0.5
A
At that point, it’s able to find (w/h)se and (w/h)so by applying Zose and Zoso (as Zc) to the single line microstrip equations. Now it comes to a point where it reach the w/h and s/h for the desired coupled microstrip line using a family of approximate equations as following
W
S
L
(mm)
(mm)
(mm)
108.19
39.28
1.139
0.297
23.78
93.60
37.67
1.508
0.3184 23.42
83.41
37.58
1.82
0.37
93.60
37.67
1.508
0.3184 23.42
108.19
39.28
1.139
0.297
23.09
23.78
The final filter layout of edge coupled with all the determined dimensions is illustrated in Figure 3.1 (3a)
(3b) The microstrip transmission line by an overall dielectric constant in order to assume TEM propagation. There are a number of formulas, listed for the calculation of eff . The most basic formula is given by Pozar as follows: [2]
re
r 1 r 1 2 2
Figure 3.1: Layout of a five-pole band-pass filter
1 12 h 1 W
Once the effective dielectric constant of a microstrip is determined, the guided wavelength of the quasi-TEM mode of microstrip is given by
2
Figure 3.2: A 3D view 5 pole band-pass filter Now in hairpin filter we reduce the size of edge coupled bandpass filter The final filter layout of Hairpin Filter with all the determined dimensions is illustrated in Figure 3.3
Figure 4.1 plot of S11 and S21 versus frequency giving the center frequency as 1.9 GHz for fr4 Substrate.(Edge Coupled Type)
Figure 4.2: Plot of current distribution of filter at frequency of 1.77 Ghz
Figure 3.3: Layout of a five-pole band-pass Hairpin filter IV. RESULTS AND ANALYSES The response is shown in Figure 4.1. As shown in figure, it gave a center frequency of 1.9 GHz. Spurious modes which do appear due to in-homogeneities of the microstrip [7, 8] are not shown here.
Figure 4.3 plot of S11 and S21 versus frequency giving the center frequency as 1.9 GHz for fr4 Substrate.(Hairpin Filter Type)
V.CONCLUSION The microstrip bandpass filter is simulated. The layout of the final filter design with all the determined dimensions is illustrated. The hairpin filter is more compact in size as compare to edge coupled filter the size of hairpin filter is 30*32 mm. The input and output resonators are slightly shortened to
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compensate for the effect of the tapping line and the adjacent coupled resonator. The EM simulated performance of the filter is shown in Figure 4.1, 4.2 and 4.3. This filter finds applications in GSM,GPS and Bluetooth applications. VI.FUTURE WORK Physical development and measurement of RF filters design for more accurate design. Use additional software such as ADS simulations and Genesys simulations to compare the results with sonnet to accurately determine the final design. REFERENCES [1] Matthaei, L. Young, and E. M. T. Jones, Microwave Filters, ImpedanceMatching Networks, and Coupling Structures. Boston, MA: Artech House, 1980. [2]D. M. Pozar, “Microwave Engineering”, Second Edition, Wiley and Sons, 1998. [3] R. Rhea, HF Filter Design and Computer Simulation. Atlanta, GA: Noble Publishing, 1994. [4] T. Edwards, Foundations for Microstrip Circuit Design, 2nd edition, England: John Wiley & Sons Ltd.,1981. [5] N. Toledo, “Practical Techniques for designing Microstrip tapped hairpin resonator filters on FR4 laminates” 2nd National ECE Conference, Manila, Philippines, November 2001. [6] Eagleware Corporation, “ TLine Program,” Genesys version 8.1, Norcross, GA, May 2002. [7] T. Yamaguchi, T. Fujii, T. Kawai, and I. Ohta, “Parallel-coupled microstrip filters with periodic oating conductors on coupled-edges for spurious suppression," IEEE MTT-S International Microwave Symposium Digest, 2008. [8] K. Singh, “Design and analysis of novel microstrip filter at l-band," in Agilent EESoF 2005 India User Group Meeting, 2005.
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