design of parallel coupled microstrip bandpass …atmsindia.org/tech_papers/2015/40design of...
TRANSCRIPT
ATMS INDIA
2015
Design of Parallel Coupled Microstrip Bandpass
Filter for IRNSS Navigation system
Abstract— Satellite filters cover a large frequency range
depending on the specific service offered by the satellite
payload. In general the navigation satellite systems are
naturally activated in the L and S bands (1-2 GHz, 2 -4 GHz,
respectively). Indian Regional Navigation Satellite System
(IRNSS) provides exclusive navigation services in L5 band and
S band frequencies. This paper describes the proto model
design calculations and its simulation for parallel coupled
microstrip bandpass filter (BPF) for L5 and S band using
MATLAB and Agilent Advanced Design system (ADS). The
design process starts with the design methodology, filter design
using MATLAB, layout design using Agilent ADS. Finally, the
filter design results are presented at the end of the paper.
Keywords— IRNSS, bandpass filter, L5 band, S band,
MATLAB, ADS
I. INTRODUCTION
Indian Regional Navigation Satellite System (IRNSS) is
an independent, indigenously developed satellite navigation
system fully planned, established and controlled by the
Indian Space Research Organization (ISRO). The IRNSS
would provide two services, with the Standard Positioning
Service open for civilian use and the Restricted Service,
encrypted one, for authorized users (military). It will provide
an accurate real time Position, Navigation and Time (PNT)
services to users on a variety of platforms with 24x7 service
availability under all weather conditions.
The INRSS consists of three segments: space, ground
and user. The space segment consists of a constellation of
seven satellites: three GEOs (Geostationary Orbit) located at
34° E, 83° E and 131.5° E and four GSOs (Geosynchronous
Orbit) placed at inclination of 29° with longitude crossing at
55° and 111° East. IRNSS ground segment consists of
ground stations for generation and transmission of navigation
parameters, satellite control, satellite ranging and monitoring.
The user segment consists of a specially designed dual
frequency receiver. Several types of receivers are planned
with single and dual frequency reception. All the seven
IRNSS satellites will be continuously tracked by the user
receiver. IRNSS provides two basic services such as Standard
Positioning Service (SPS) for common civilian users and
Restricted Service (RS) for special authorized users. Each
IRNSS satellite provides SPS signals in L5 and S bands. The
IRNSS SPS service is transmitted on L5 (1164.45 – 1188.45
MHz) and S (2483.5-2500 MHz) bands. The Table (I)
summarize the list of mid frequencies and its bandwidth of
the navigation bands.
TABLE I. CARRIER FREQUENCIES AND BANDWIDTHS
Signal Carrier
Frequency Bandwidth
SPS – L5 1176.45 MHz 24 MHz (1164.45 -1188.45
MHz)
SPS – S 2492.028 MHz 16.5MHz (2483.50 -
2500.00MHz)
In this work we have designed bandpass filter for these
two bands of frequency in L5 and S band with parallel
coupled microstrip filter. Our goal is to achieve high
accuracy in obtaining the required designed parameters
(center frequency, return loss and insertion loss). The design
and simulation are performed using Agilent ADS. The
design equations are calculated and the filter response is
verified using MATLAB.
II. PARALLEL COUPLED BANDPASS FILTER
The microwave filter is a two port network which used
to control the frequency response by providing transmission
at frequencies within the passband and attenuation in the
stopband of a filter. Filters are an essential part of tele-
communications and radar systems. Of its low-cost
fabrication, easy integration and simple designing procedure,
the parallel coupled-line filters are widely used in
microwave microstrip circuits. A bandpass filter only passes
the frequencies within a certain desired band and attenuates
others signals whose frequencies are either below the lower
cutoff frequency or above the upper cut-off frequency [1].
The range of frequencies that a bandpass filter passes
through is referred as passband.
Microstrip technology is a good candidate for filter
design due to its advantages of low cost, compact size, light
weight, planar structure and easy integration with other
components on a single board. In Coupled Transmission
lines, coupling between two transmission lines is introduced
by their proximity to each other [2]. Coupling effects may be
undesirable, such as crosstalk in printed circuits, or they may
be desirable, as in directional couplers where the objective is
to transfer power from one line to the other and another of
their major use is using them in filtering the microwave
range frequencies. The filter response will be based on the
Tchebyscheff transfer function. Tchebyscheff type filters are
popular for their high selectivity, i.e., they have a relatively
fast signal cut off between pass and stop band [3]. Filters
Jim Godwin.R.S1, Vineeth.V2,S. Purushothaman3, Dr. S. Raghavan4 1,2,4 Department of ECE, National Institute of Technology, Trichy-620015, India
3 EDMD/SIG, ISRO Satellite Centre, Bangalore-560017, India
Email: [email protected], [email protected], [email protected]
ATMS INDIA
2015
operating in giga hertz frequency ranges rely on distributed
transmission line structures to obtain the desired frequency
response.
III. DESIGN METHODOLOGY
A. Filter Elements Calculation
Fig (1) illustrates a general structure of parallel-coupled
microstrip bandpass filters that use half wavelength line
resonators. They are positioned such that adjacent resonators
are parallel to each other along half of their length.
Fig. 1. General structure of parallel coupled microstrip bandpass filter
The design equations for this type of filter are given by [3],
𝐽0,1
𝑌0=
𝜋
2
∆
𝑔0𝑔1 (1a)
𝐽 𝑗 ,𝑗+1
𝑌0=
𝜋 ∆
2 𝑔𝑗𝑔𝑗+1 , j=1, 2,… , n-1
(1b)
𝐽𝑛 ,𝑛+1
𝑌0=
𝜋
2
∆
𝑔𝑛𝑔𝑛+1 (1c)
Where 𝑔0, 𝑔1,… ,𝑔𝑛are the element of a ladder-type low-
pass prototype with a normalized cutoff frequency Ωc = 1,
and Δ is the fractional bandwidth of band-pass filter.
𝐽𝑗 ,𝑗+1are the characteristic admittances of J-inverters and Y0
is the characteristic admittance of the terminating lines. To
realize the J-inverters obtained above, the even mode and
odd mode characteristic impedances of the coupled
microstrip line resonators are determined by,
(𝑧0𝑒)𝑗 ,𝑗+1 = 1
𝑌0 1 +
𝐽 𝑗 ,𝑗+1
𝑌0+
𝐽 𝑗 ,𝑗+1
𝑌0
2 ,
j=0, 1, …, n (2a)
(𝑧0𝑜)𝑗 ,𝑗+1 = 1
𝑌0 1 −
𝐽 𝑗 ,𝑗+1
𝑌0+
𝐽 𝑗 ,𝑗+1
𝑌0
2 ,
j=0, 1, … , n (2b)
For Tchebyscheff filters having resistor terminations at both
ends, 𝐿𝐴𝑟 db pass-band ripple, 𝑔0 = 1, the element values
may be computed as follows.
First compute,
𝛽 = 𝑙𝑛 𝑐𝑜𝑡ℎ𝐿𝐴𝑟
17.37 (3a)
𝛾 = 𝑠𝑖𝑛ℎ 𝛽
2𝑛 (3b)
𝑎𝑘 = 𝑠𝑖𝑛 2𝑘−1 𝜋
2𝑛 (3c)
𝑏𝑘 = 𝛾2 + 𝑠𝑖𝑛2 𝑘𝜋
𝑛 , k = 1, 2, …, n (3d)
𝑔1 = 2𝑎1
𝛾 (3e)
𝑔𝑘 = 4 𝑎𝑘−1𝑎𝑘
𝑏𝑘−1𝑔𝑘−1, k = 2, 3, …, n (3f)
𝑔𝑛+1 = 1 , 𝑛 𝑜𝑑𝑑
𝑐𝑜𝑡ℎ2 𝛽
4 , 𝑛 𝑒𝑣𝑒𝑛
(3g)
Find element values (g) using (3a – 3g). And then find the
odd mode and even mode impedances using equations (1a –
1c) and (2a, 2b).
B. Microstrip Layout Design
Further in the filter design, find the dimensions of
coupled microstrip lines that exhibit the desired even mode
and odd mode impedances. First, determine equivalent
single microstrip shape ratios (w/h). Subsequently, it can
relate coupled line ratios to single line ratios.
For a single microstrip line,
𝑍0𝑠𝑒 = 𝑍0𝑒 𝑗 ,𝑗+1
2 (4a)
𝑍0𝑠𝑜 = 𝑍0𝑜 𝑗 ,𝑗+1
2 (4b)
Find (𝑤/ℎ)𝑠𝑒 and (𝑤/ℎ)𝑠𝑜 from 𝑍0𝑠𝑒and 𝑍0𝑠𝑜 .
𝑊
ℎ=
8 𝑒𝑥𝑝 𝐴
𝑒𝑥𝑝 2𝐴 −2 (5a)
𝐴 = 𝑍𝑐
60 𝜀𝑟+ 1
2
0.5+
𝜀𝑟−1
𝜀𝑟+1 0.23 +
0.11
𝜀𝑟 (5b)
At this point, we are able to find (𝑤/ℎ)𝑠𝑒and(𝑤/ℎ)𝑠𝑜 . Next
step is to find the w/h and s/h for the desired coupled
microstrip line using a family of approximate equations as
following.
𝑠
ℎ=
2
𝜋𝑐𝑜𝑠ℎ−1
𝑐𝑜𝑠ℎ
𝜋
2
𝑊
ℎ 𝑠𝑒 + 𝑐𝑜𝑠ℎ
𝜋
2
𝑊
ℎ 𝑠𝑜 − 2
𝑐𝑜𝑠ℎ 𝜋
2
𝑊
ℎ 𝑠𝑜 − 𝑐𝑜𝑠ℎ
𝜋
2
𝑊
ℎ 𝑠𝑒
(6a)
ATMS INDIA
2015
𝑤
ℎ=
1
𝜋 𝑐𝑜𝑠ℎ−1
1
2 𝑐𝑜𝑠ℎ
𝜋𝑠
2ℎ − 1
+ 𝑐𝑜𝑠ℎ 𝜋𝑠
2ℎ + 1 𝑐𝑜𝑠ℎ
𝜋
2
𝑊
ℎ 𝑠𝑒
− 𝜋𝑠
2ℎ
(6b)
The effective dielectric constant is given by
𝜀𝑟𝑒 = 𝜀𝑟+1
2+
𝜀𝑟−1
2
1
1+12ℎ
𝑤
(7a)
Once the effective dielectric constant of a microstrip is
determined, the guided wavelength of the quasi-TEM mode
of microstrip is given by
𝜆𝑔 = 𝜆0
𝜀𝑟𝑒 (8a)
𝑙 = 𝜆𝑔
4 (8b)
IV. DESIGN AND SIMULATION
The two navigation bands of filters having center
frequency of 1.1764 GHz and 2.4920 GHz and bandwidth of
24 MHz and 16.5 MHz respectively are designed with the
stopband attenuation of 50 dB. The dielectric constant of the
substrate is taken as 4.4 (FR4 epoxy). The order of the filter
for this specification is 3. For this specification, the above
equations have been implemented using MATLAB [9] and
the results are as shown below.
TABLE II. EVEN AND ODD MODE IMPEDANCES
𝐧 𝐠𝐤
𝐟𝐜 = 𝟏.𝟏𝟕𝟔𝟒𝟓 𝐆𝐇𝐳 𝐟𝐜 = 𝟐.𝟒𝟗𝟐𝟎𝟐𝟖 𝐆𝐇𝐳
𝒁𝒐𝑱𝒏 𝒁𝒐𝒆* 𝒁𝒐𝒐
* 𝒁𝒐𝑱𝒏 𝒁𝒐𝒆* 𝒁𝒐𝒐
*
1 1.5963 0.1416 58.0877 43.9196 0.0807 54.3612 46.2902
2 1.0966 0.0242 51.2402 48.8183 0.0079 50.3960 49.6101
3 1.5963 0.0242 51.2402 48.8183 0.0079 50.3960 49.6101
4 1.0000 0.1416 58.0877 43.9196 0.0807 54.3612 46.2902
* Impedance in ohm
TABLE III. w/h AND s/h RATIOS FOR LAYOUT
𝐧
𝐟𝐜 = 𝟏.𝟏𝟕𝟔𝟒𝟓 𝐆𝐇𝐳 𝐟𝐜 = 𝟐.𝟒𝟗𝟐𝟎𝟐𝟖 𝐆𝐇𝐳
𝐰
𝐡
𝐬
𝐡
𝐰
𝐡
𝐬
𝐡
1 2.0150 0.2944 2.1189 0.5776
2 2.1697 1.3063 2.1744 2.0193
3 2.1697 1.3063 2.1744 2.0193
4 2.0150 0.2944 2.1189 0.5776
Table II shows the element values of the 3rd
order
Tchebyscheff filter, even mode and odd mode impedances.
Microstrip layout design parameters of parallel coupled
bandpass filters is found and listed in Table III. The layout
design implemented using MATLAB is shown in fig. 2 and
fig. 3 for L5 band and S band respectively.
Fig. 2. Layout design for fc = 1.1764 GHz using MATLAB
Fig. 3. Layout design for fc = 2.4920 GHz using MATLAB
For the substrate thickness of 1.588 mm and 𝜀𝑟 = 4.4,
the layout was designed using Agilent ADS [8]. This is
shown in fig. 4 and fig. 5 for L5 band and S band
respectively.
Fig. 4. Layout design for fc = 1.1764 GHz using Agilent ADS
ATMS INDIA
2015
Fig. 5. Layout design for fc = 2.4920 GHz using Agilent ADS
V. RESULTS AND DISCUSSION
The simulated filter structure and response is shown in
fig. 6 and fig. 7. In the response graph, gain (dB) is plotted
on the Y axis and frequency (GHz) on the X axis. It is clear
that the simulated midband frequency is found to be 1.1764
GHz and 2.4920 GHz for L5 and S-band frequencies
respectively. The band edge frequencies of L5 band filters
are 1.1640 GHz and 1.1880 GHz. The values of insertion
loss (S12) and return loss (S11) at 1.1764 GHz are -0.1 dB and
-44.604 dB respectively. Similarly the band edge frequencies
of S band filters are 2.4830 GHz and 2.5 GHz. The values of
insertion loss (S12) and return loss (S11) at 2.4920 GHz are
-0.1 dB and -66.317 dB. The simulation results of the
designed filters are shown in fig. 6 and fig. 7.
Fig. 6. S11 and S12 for fc = 1.1764 GHz using Agilent ADS
Fig. 7. S11 and S12 for fc = 2.4920 GHz using Agilent ADS
VI. CONCLUSION
The filters are one of the primary and essential parts of
the microwave system and any communication system. Any
communication system cannot be designed without filters.
Our designed parallel coupled microstrip bandpass filter
operates with a bandwidth of 24 MHz at a center frequency
of 1.1764 GHz and bandwidth of 16.5MHz at a center
frequency of 2.4920 GHz which falls in the L5 and S-band
navigation frequencies respectively. In general IRNSS
system needs compact, low cost high performance bandpass
filter. The designed proto model of parallel coupled
microstrip band pass filter fulfills the entire requirement of
IRNSS navigation system.
VII. REFERENCES
[1] G. Mathaei, L.Young& E.M.T. Jones, “Microwave Filter impedance
matching networks and coupling structures,” Artech House, Norwood,
MA, 1980
[2] S.B.Cohn “Parallel Coupled transmission line resonator filters” IRE
Transaction.Microwave Theory Tech,Vol,PP 223-231, April1958 [3] D. M. Pozar, “Microwave Engineering”, Second Edition, Wiley and
Sons, 1998.
[4] T. C. Edwards, Foundations for Microstrip Circuit Design, 2nd edition, England: John Wiley & Sons Ltd.,1981.
[5] R. Levy and S. B. Cohn, “A history of microwave filter research, design and development,” IEEE Trans. Microwave Theory Tech., vol.
MTT-32, pp. 1055–1067, Sept. 1984.
[6] B. Easter and K. A. Merza, “Parallel-coupled-line filters for inverted-microstrip and suspended-substrate MIC’s,” in 11th Eur. Microwave
Conf. Dig., September 1981, pp. 164–167.
[7] M. Makimoto and S. Yamashita, “Compact bandpass filters using stepped impedance resonators; Prvc. IEEE, vol. 67, pp. 16-19, Jan.
1979.
[8] http://www.agilent.com/ [9] http://in.mathworks.com/