Dual-Band RHCP Stacked Microstrip Antenna for IRNSS Receiver · According to the ICD of IRNSS Standard Positioning Services, the minimum received power of IRNSS signals shall be -162.3dBW

Dual-Band RHCP Stacked MicrostripAntenna for IRNSS Receiver

Praveen Chandran C.R1, Mudumba Ramesh2

and S. Raghavan3

1Master Control Facility,Indian Space Research Organisation,

Hassan, Karnataka 573201, [email protected]

2 3Department of Electronics andCommunication Engineering,

National Institute of Technology,Tiruchirappalli, Tamilnadu - 620015, India

[email protected] and [email protected]

January 2, 2018

Abstract

Objectives: This paper presents the design aspects andsimulation of a right-hand circularly polarized, dual-band,two layer stacked micro-strip antenna for IRNSS receiverfront-end operating at L5 band (1176.45 MHz) and S band(2492.028 MHz) frequencies.

Methods: IRNSS satellites transmit navigational sig-nals in L5 (1176.45 MHz) and S (2492.028 MHz) frequencybands. Dual-band antenna is preferred to mitigate the ef-fect of Ionosphere on the IRNSS signal. Two layer stackedpatch structure is adopted for the proposed antenna withthe bottom patch designed for L5 band and top patch for Sband. Right-Hand Circularly Polarized operation with Ax-ial Ratio less than 2dB is achieved by introducing a pair ofsquare shaped notches at the diagonally opposite sides of

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International Journal of Pure and Applied MathematicsVolume 118 No. 17 2018, 47-59ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu

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the patches and a single probe feed along the center of theantenna.

Findings: The proposed antenna is compact and ex-hibits dual frequency RHCP operation with axial ratio lessthan 2dB. The antenna radiation pattern is hemisphericalin nature with broad beam width for good sky visibility.Antenna has reasonably good gain and cross polarisationisolation.

Improvements: This antenna design is a good candi-date for IRNSS receiver applications. However future re-search works are planned to introduce the concept of meta-materials using complementary split ring resonators (CSRR)for miniaturization and planar layout. Such a design wouldbe ideal for mobile receiver applications.

Key Words : IRNSS, GNSS, Stacked Patch, CornerNotch, Axial Ratio

1 Introduction

Global Navigation Satellite Systems (GNSS) is becoming key tech-nological achievement in modern world along with Internet and Mo-bile communications. GNSS offers a wide variety of services suchas navigation, positioning, public safety, surveillance, geographicsurveys, time standards, mapping and weather and atmosphericinformation. The presence of GNSS applications became ubiqui-tous ever since its integration with portable personal navigationsdevices and mobile phones. GPS is the pioneer among the GNSSsystems, which is 24 MEO satellite constellation and provides 7.1mposition accuracy with 95% confidence level. GLONASS is a spacebased navigation system operated by Russia and provides 7.5 m po-sition accuracy with 95% confidence level. Galileo is the Europeanequivalent GNSS system and provides 4m position accuracy withdual-frequency receiver. BeiDou is a Chinese GNSS system which,upon completion by 2020, is expected to give positional accuracyof 10m1.

Indian Regional Navigation Satellite System (IRNSS) is the newentrant in the domain of Space Based Positioning and NavigationalSystem. IRNSS is an autonomous regional satellite navigation sys-

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tem being developed by the Indian Space Research Organizationwhich would be under complete control of the Indian government.The requirement for a completely indigenous navigation system isrelevant since access to foreign government controlled navigationsystems is not guaranteed during hostile situations in the presentglobal scenario.

IRNSS envisages establishment of Regional Navigation SatelliteSystem using a combination of GEO and GSO Space crafts overIndian region. The IRNSS constellation will consist of seven satel-lites - three Satellites in GEO orbit (at 32.5o E, 83o E and 131.5o

E) and four Satellites in GSO orbit inclined at 29o to the equatorialplane with their longitude crossings as 55o E and 111.75o E (two ineach plane). All the satellites are visible in the Indian region for24hours. The intended service area for IRNSS is primarily the In-dian Land Mass. The service area for IRNSS is in general specifiedas between longitude 40o east to 140o east and between latitude ±40o. The IRNSS System is expected to provide two sigma positionaccuracy better that 20 meters over India and a region extendingto the about 1500 kilometers around India. The proposed IRNSSsystem operation will be in two frequency bands, namely L5 and S.On each of these frequencies, two services are available, StandardPositioning Services (SPS) for civilian users and Restricted Services(RS) exclusively for specific users [2,3,4].

Antenna is the first element of the IRNSS receiver to receivethe signals originated from the satellites located at different orbitalslots. The integrity of the processed data improves if the receiverantenna is capable of receiving signals from as many satellites aspossible. In this paper a dual-band circularly polarized antennais proposed for IRNSS receiver. The antenna is capable of receiv-ing the signals from IRNSS satellites at both L5 (1176.45 MHz)band and S (2492.028 MHz) bands. This proposed antenna is de-signed using Ansoft High Frequency Simulation Software (HFSS)which uses Finite Element Method to generate accurate solution.The simulated antenna parameters are compared against the designrequirements and are discussed.

This paper is organized as follows. Section 2 describes reviewof some of the available literature GNSS terminal antennas. Designspecifications of the antenna are given in Section 3. Section 4 de-scribes the design methodology used for the proposed stacked patch

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antenna. Section 5 gives the simulation results and its comparisonagain the design values. Finally, the concluding remarks are givenin Section 6.

2 Related Works

Past decade has seen the proliferation of a variety of electronicterminal devices integrated with global positioning, navigation ser-vices and hence much research works had happened in the designof terminal antennas for such devices. Many literature works havebeen published on GPS receiver antennas due to the wide spreaduse of GPS based applications. IRNSS is still in development phaseand its associated services will be made available for usage only inthe upcoming years. Hence only very few technical literatures areavailable which deals with IRNSS receiver antennas. Still many ofthe design considerations valid for GPS receiver antennas are moreor less equally applicable for IRNSS receiver antennas also. Some ofthe technical literatures available on other GNSS receiver antennasare reviewed and presented below.

A small slot-loaded, proximity-fed patch antenna is designed forGPS operation at L1 (1575 MHz) and L2 (1227 MHz) bands. High-dielectric substrate and meandered slots are employed to reduce theantenna size down to 25.4 mm in diameter and 11.27 mm in thick-ness. The thickness is important for achieving the wide bandwidthin support of modern GPS coding schemes. The dual-band cover-age is achieved by utilizing the patch mode in L2 band and slotmode in L1 band. This design features additional slot stubs forindependently tuning the L1 frequency. The right-hand circularlypolarized field property is achieved by connecting two proximityprobes to a small surface-mount 0 to 90 degree hybrid chip5.

A circularly polarized microstrip antenna with low wide-angleaxial-ratio design is available for tri-band GPS applications. Theantenna is designed for global positioning satellite operations at1227MHz (L2), 1575MHz (L1) and 1176MHz (L5, available after2007). This antenna has another advantage of a much wider bandin both VSWR and 3 dB axial-ratio compared with single-fed GPSantennas6.

A spiral antenna array on RT/DUROID Substrate for the oper-

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ating frequency range of 1.2 to 1.6GHz uses four spiral elements toprovide broadband satellite coverage and can also be used in con-junction with a space-time adaptive processor (STAP) for interfer-ence suppression. The antenna and integrated feed parameters areoptimized for the L1 and L2 band radiation coverage. This antennawas showing remarkable performance over the frequency L5 (1175MHz) with high gain of 9 dB and high directivity. But the proposedantenna design is for single frequency (L5) operation7.

A triangular fractal patch antenna for IRNSS and GAGAN ap-plications uses substrate with dielectric constant of 4.8 and thick-ness of 3.05 mm. The antenna exhibits multi-band resonant fre-quencies at the frequency L5 (1175 MHz), L1 (1575.42MHz) and S(2492.08MHz). The antenna exhibits good return loss at the spec-ified frequencies. At 1176.42MHz frequency range the antenna hasa return loss of about -14dB and at the 1575.42MHz range it ishaving a return loss of nearly -17dB while it is having a return lossof -15dB at the frequency range of 2492.08MHz. The gain of theantenna is 5.052dB and the directivity of the antenna is given as6.29723dB8.

3 Antenna Design Specifications

Some of the key requirements and technical challenges involved indesigning a suitable antenna for IRNSS receiver are mentioned here.The intended design should be small, lightweight and compact aspossible to be accommodated in a terminal device. The fabricationcost also should be minimal.

Dual-band antenna is preferred to mitigate the effect of Iono-sphere on the IRNSS signal. The major effect of ionosphere onIRNSS signals is frequency-dependent phase shift (group delay)caused by the dispersive characteristics of the ionosphere. This ad-verse effect is effectively reduced by employing two widely spacedfrequencies. Redundancy and increased resistance to jamming arethe other benefits offered by dual band operation. Hence the pro-posed antenna should be capable of dual-band operation1,2.

Impedance bandwidth is the frequency range over which 90%of the incident power will be delivered to the antenna i.e. thereflection coefficient S11 less than -10dB and the VSWR is less than

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2:1. IRNSS signals will be occupying a bandwidth of 24 MHz inL5 band (1164.45-1188.45 MHz) and 16.5 MHz in S band (2483.50-2500.00 MHz). The proposed antenna should have signal receptionbandwidths accordingly1,2.

According to the ICD of IRNSS Standard Positioning Services,the minimum received power of IRNSS signals shall be -162.3dBWand maximum value of the received signal power shall be -154.0dBW2. For any of the modern day GNSS receivers, the antennagain should be greater than 0 dBi6.

The IRNSS receiver antenna should have good sky visibility soas to receive signals from maximum number of satellites. Hencethe radiation pattern should be hemispherical in nature with broadbeam width. Elevation angles near and slightly below horizon areof specific interest because intentional jamming or unintentionalinterference signal sources are most likely to originate. So the an-tenna radiation pattern should show sharp drop-off for elevationangle near and below zero degree1.

Use of CP for GNSS signals transmission and reception elim-inates the need of polarization alignment which would have beenneeded for Linear or Elliptical Polarization. IRNSS satellites trans-mit signals in right hand circular polarization hence the use of lin-early polarized antenna at receiver end would cause 3dB loss dueto polarization mismatch. For optimal performance the proposedreceiver antenna should be of RHCP. If antennas are not havingperfect polarization, an RHCP antenna will pick up some of theLHCP energy. The quality of circular polarization is described interms of Axial Ratio. For IRNSS receiver antennas the axial ratioshould be less than 2dB9.

Many of the design requirements for IRNSS terminal antennasare often conflicting with one another due to the restrictions im-posed by size, weight, compactness and performance characteristics.

4 Design Methodology

Helix and Patch antennas are the most widely used types in GNSSreceiver applications. When it comes to designing antennas forterminal devices, integrating the antenna into the actual device is ofprimary concern. Patch antennas are ideal for an application where

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the antenna sits on a flat surface. Patch antennas can provide highgain, especially if they are mounted on top of a large ground plane.Fabrication cost can also be reduced by using substrate materialslike FR-4 or even air as a dielectric. Hence patch antenna baseddesign is chosen for the intended IRNSS terminal antenna.

Microstrip antenna with multi-frequency operation has beenachieved by several techniques like single-patch with shorting pinsor by introducing slots of different shapes in the patch surface,multi-layer structure and multi-feed planar antenna etc. Usingmulti-layer structure is the easiest way to achieve multi-frequencyoperation than using other approaches. The dimensions of eachpatch determines the individual resonant frequencies and by vary-ing the patch dimensions, the specific resonant frequencies can bechanged without affecting the other frequencies. The proposed de-sign has multi-layer square patches where the side length is cal-culated using the equation given in10. The width of the patch ischosen to be same as that of length in order to have a square patchstructure. The upper patch designed to resonate at 2492.028MHz(S-Band) and the lower patch length is designed for 1176.45MHz(L5 Band) of operation. RT/Duriod 5880 with dielectric constantof 2.2 is chosen as substrate for upper patch whereas FR4 Epoxywith dielectric constant of 4.4 is selected for lower patch. Thicknessof the substrate is chosen as 0.187 inches (4.75 mm). The groundplane is selected to be 100 mm × 100 mm in dimension. Both theupper and lower patches are fed by the same 50 Ohm Co-Axial feedline. Fig 1 shows the top and side views of the proposed antenna.

Some of the methods for obtaining CP using single feed are di-agonally fed nearly square, square with stubs and notches along thetwo opposite edges, corner-chopped squares, squares with a diag-onal slot etc. The proposed design uses square notch cuts at thediagonally opposite corners of the square patches. The dimensionsof the microstrip antennae are modified such that the resonancefrequencies of the two orthogonal modes are close to each other.The antenna is excited at a frequency in between the resonancefrequencies of these two modes, such that the magnitude of the twoexcited modes are equal. Also, the feed-point location is selectedin such a way that it excites the two orthogonal modes with phasedifference of +45o and -45o with respect to the feed point, whichresults in phase quadrature between the two modes. These two con-

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ditions are sufficient to yield CP. The size of the square notches atthe diagonally opposite corners of the square patches and the sin-gle feed location is optimized so as to produce right hand circularlypolarized radiation pattern with axial ratio less than 2dB11.

Figure 1: Schematic Layout of Stacked Patch Antenna

Table 1: Antenna Dimensions

DimensionUpper Patch

(S-band)Lower Patch(L5-band)

Square Side Length 36.9 mm 57.15 mmSubstrate Thickness 4.75 mm 4.75 mmCorner Notch Size 4.9 mm 6.4 mm

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5 Simulation Results

Simulation results are found to be satisfying in accordance to thedesign requirements. Fig 2 shows the measured return loss resultsof the designed antenna. The measured return loss is below -10dBat both L5 and S bands.

Figure 2: Return Loss (S11 in dB) Vs Frequency (GHz)

The -10dB impedance bandwidths of the antenna, 50 MHz (1.16to 1.21 GHz) centered around 1.17645 GHz (L5 band) and 90 MHz(2.44 to 2.53 GHz) centered on 2.492028 GHz (S band), meetsthe design requirement. Use of thicker substrate ensures sufficientimpedance bandwidth. The gain of the antenna is found to be1.02dB and 6.73 dB at 1.17645 GHz and 2.492028 GHz respectively.

Fig. 3 given below shows the 3D ration pattern measured at L5and S bands through simulation. The radiation pattern is foundto be hemispherical is shape with maximum gain in the directionnormal to the plane of the patch.

Figure 3: Radiation Pattern (3D) of the Antenna

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The antenna produces right-hand circularly polarized waves.Both co-pol (RHCP) and cross-pol (LHCP) radiation patterns atL5 and S bands are measured and are shown in Fig. 4 and Fig. 5respectively.

Figure 4: Radiation Pattern (2D) of the Antenna at L5 band

Figure 5: Radiation Pattern (2D) of the Antenna at S band

From Fig.4 and Fig. 5, it is clear that the antenna exhibits goodcross polarisation separation at both L5 and S band frequencies.The performance of a circularly polarized antenna is characterizedby its Axial Ratio (AR). AR is defined as the ratio of orthogonalcomponents of an E-field. For a perfectly circularly polarized an-tenna AR will be 1 or 0 dB and for a linearly polarized antenna AR

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will be infinity. Generally AR in the range of 3 to 6 dB will be suf-ficient for most of the practical applications. By carefully choosingproper corner notch dimensions, the proposed antenna has achievedAR values below 2 dB in L5 and S bands.

6 Conclusions

In this paper, a dual-band right hand circularly polarized stackedpatch antenna design for IRNSS receiver is proposed. Accuracyand integrity of received data is highly imperative for IRNSS basedpositioning and navigational services and hence the antenna designhas to be carried out against the stringent design requirements. Theproposed antenna characteristics like return loss, gain, impedancebandwidth, cross polarization separation and axial ratio are foundto suitable for IRNSS receiver applications.

7 Acknowledgements

The first author sincerely thank Prof. S Raghavan and Mr. MudumbaRamesh for their invaluable support and guidance towards the suc-cessful completion of the project. First author thankfully acknowl-edge the technical and moral support given by the authorities ofMaster Control Facility, Indian Space Research Organization dur-ing the course of project work.

References

[1] Xiaodong Chen, Clive G Parini, Brian Collins, Yuan Yao. Ma-sood Ur Rehman. Antennas for Global Navigation SatelliteSystems. 1st edn. Wiley, 2012.

[2] IRNSS Signal In Space ICD for Standard Positioning Service.June 2014. ISROIRNSS-ICD-SPS-1.0, Indian Space ResearchOrganization, Bangalore.

[3] Kibe SV, Gowrishankar D. Indias Satellite Navigation Pro-gramme. APRSAF -15: Space for Sustainable Development,December 10th 2008, Vietnam.

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[4] Indian Regional Navigation Satellite System (IRNSS).K.N.Suryanarayana Rao. Project Director-IRNSS. ISAC Ban-galore.

[5] Ming Chen, Chi-Chih Chen. A Compact Dual-Band GPSAntenna Design. IEEE Antennas Wireless Propagation Let-ters.2013 vol.12, pp.245-248.

[6] Zhang Y Q. Li X. Yang L. Gong S X. Dual-Band CP Antennawith Low Wide-Angle Axial ratio for Tri-Band GPS Applica-tions. Progress In Electromagnetics Research C. 2012 Vol. 32,pp.167-179.

[7] B Sada Siva Rao. T Raghavendra Vishnu. Habibulllah Khan. DVenkata Ratnam. Spiral Antenna Array Using RT-Duroid Sub-strate for Indian Regional Navigational Satellite System. In-ternational Journal of Soft Computing and Engineering. 2012May, Volume-2, Issue-2. ISSN: 2231-2307.

[8] Arivazhagan S, Kavitha K, Prashanth HU. Design of a tri-angular fractal patch antenna with slit IRNSS and GAGANapplications. Proceedings of ICICES, India, 2013.

[9] Request for Proposal for the Development of IRNSS SPS GPSUser Receivers, v.1.0, March 2014, Space Application Center,ISRO, Ahmedabad.

[10] Ramesh Garg, Prakash Bhartia, Inder J Bahl, Apisak Ittip-iboon, Microstrip Antenna Design Handbook. Artech House,2001.

[11] Girish Kumar, KP 0Ray. Broadband Microstrip Antennas.Artech House, 2003.

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Documents

Dual-Band RHCP Stacked Microstrip Antenna for IRNSS Receiver · According to the ICD of IRNSS Standard Positioning Services, the minimum received power of IRNSS signals shall be -162.3dBW