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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: jimgodwin24@gmail.com, vvineeth1993@gmail.com, purusho@isac.gov.in

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)

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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

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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/