Essay: Coplanar multifunctional microstrip antenna for both global positioning system (GPS) and Bluetooth application

Abstract: Due to rapid development of wireless communication systems, various services are of very much importance in today’s day-to-day life. In order to improve the utility efficiency of the limited spectra and spatial resources, different services using the same antenna are required. Such system is presented here. This paper presents coplanar multifunctional microstrip antenna for both global positioning system (GPS) and Bluetooth application. Our antenna consists of two parts: outer square ring patch antenna and centre-fed square patch antenna. Coplanar, simple, single line feeding technique is used for square ring patch antenna which operates with right handed circular polarization at 1.58GHz (GPS L1). Outer square ring is also used to load inner center-fed square patch antenna operating with vertical linear polarization at 2.4GHz for Bluetooth application. Simulation results of this antenna in HFSS are also presented here. Good match is achieved between simulation results in HFSS and hardware measurement. Hence this paper emphasizes on multifunctional microstrip antenna which can radiate or operates on two different frequencies simultaneously.

Keywords’ Coplanar, square ring, polarization, microstrip.


Today number of electronic gazettes including the devices such as laptop, mobile, PDA, Digital Cameras are integrated and remotely connected with Wi-Fi, GPS, Bluetooth applications which further supports the 3G/4G environment. In any communication system the antenna is one of the vital and critical components. A good design of the antenna can relax system requirements and improve overall system performance. Because of the requirements with different radiation and polarization performances for different applications, conventional single-fed multiband antennas are not practical. Hence, the multifunctional antenna with different radiation characteristics has become more and more important for antenna designers. A representative example is the use of one multifunctional antenna in a vehicle to produce both a broadside circularly polarized pattern for satellite-positioning application and an omni-azimuthal radiation pattern for terrestrial mobile communication service. The reasons are that many terrestrial wireless communication applications should be location-based or require knowledge of vehicle location, which could be achieved through the use of Global Positioning System (GPS) [1].

The Global Positioning System (GPS) is a space-based Global Navigation Satellite System (GNSS) that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites. It is maintained by the US government. A GPS receiver calculates its position by precisely timing the signals sent by GPS satellites high above the Earth. All satellites broadcast at two frequencies, 1.57542 GHz (L1 signal) and 1.2276 GHz (L2 signal) [2]. The satellite network uses a CDMA spread-spectrum technique where the low-bit-rate message data is encoded with a high-rate pseudo-random (PRN) sequence that is different for each satellite. The receiver must be aware of the PRN codes for each satellite to reconstruct the actual message data.

Bluetooth is a proprietary open wireless technology IEEE 802.15.1 standard for exchanging data over short distances, from fixed and mobile devices, creating personal area networks (PANs) with high levels of security. Bluetooth is managed by the Bluetooth Special Interest Group, which has more than 16,000 member companies in the areas of telecommunication, computing, networking, and consumer electronics. Bluetooth uses a radio technology called frequency-hopping spread spectrum, which chops up the data being sent and transmits chunks of it on up to 79 bands in the range 2,400’2,483.5 MHz This range is in the globally unlicensed Industrial, Scientific and Medical (ISM) 2.4 GHz short-range radio frequency band.
Our design satisfies 2.4GHz band with vertical linear polarization for Bluetooth service [3] and 1.58GHz signal with right handed circular polarization for GPS service. Geometry of proposed antenna in this paper uses only single dielectric layer.
Rest of the paper is organized as follows: Section II describes antenna software design with its dimensions in HFSS. Simulation results are shown and described in Section III. Finally we have conclusion in Section IV.


A. Geometry of Antenna

Geometry of proposed multifunctional antenna is as shown in fig.1 bellow. It supports GPS with right handed circular polarization at 1.58GHz and Bluetooth signal at 2.4GHz band with vertical polarized omni-directional pattern simultaneously.

Fig.1 Geometry of proposed GPS/Bluetooth Integrated antenna [4].
Our geometry has two radiators i.e. outer square ring patch antenna working for GPS application with right handed circular polarization and inner square patch antenna having vertical linear polarization for Bluetooth application [1][5]. Both are placed on same substrate which is nothing but FR4 material having dielectric constant of 4.4 and square ground plane of 100×100 mm2. Two ports are used for feeding our antenna. Port 1 is for GPS application and it is called as microstrip line feeding or single line feeding. Signal is fed to feed line, which is connected to microstrip line. Shorting pin is there at the other terminal of microstrip line [6]. Shorting pin relaxes the requirements of dimensions of microstrip line. Signal flows from left to right in microstrip line; it can be considered as in clockwise direction. Due to the concept of fringing fields [1] outer square ring patch gets energized in anticlockwise direction i.e. energy flows from right to left. Which produces right handed circular polarization. Port2 is used for centre feed inner square patch for Bluetooth application. Impedance matching can be improved by using square ring to load centre fed square patch antenna. Impedance matching for Bluetooth antenna can be achieved by adjusting G1 slot.
Variation in W1 does not change reflection coefficient for Bluetooth antenna, but it tunes the resonant frequency of GPS antenna. Resonant frequency of GPS can be calculated using following formula [4]

C – Speed of light in free space i.e. 3×108 m/s,
(W1+W2) – mean circumference of square-ring antenna
??eff – effective dielectric constant i.e. 4.4.

Shortening the width of the outer square ring will obtain the higher resonant frequency for Port1 i.e. for GPS without affecting the same for Bluetooth. This is because dual resonance behavior of Bluetooth band can be observed by exciting square ring patch and square patch both. As G1 slot width decreases resonant frequency will decrease resulting in decrease in quality factor Q of antenna and widening bandwidth [4].
Polarization of electromagnetic wave is nothing but orientation of electric field vector. In case of circular polarization, two components of electromagnetic wave i.e. horizontal and vertical are same forming circular geometry of orientation. Circular polarization has advantages of reflectivity, absorption, phasing issue, multipath etc over other polarization techniques [1].
B. Specifications of the System
Dimensions of proposed antenna in millimeter is as per in Table I [4].

Parameter H W1 W2 W3 W4
Value 3 55 34 3 1
Parameter W5 L1 L2 G1 G2
Value 1.3 63 23 1 1.1
H- Thickness of the substrate.
W1- Outer side width of the square ring patch.
W2- Inner side Width of the square ring patch.
W3- Width of shorting pin.
W4- Width of Microstrip line.
W5- Diameter of probe feed line.
L1- Length of shorting pin.
L2- Length of Microstrip line.
G1- Width of ?? type admittance network.
G2- Dist. Between shorting pin & square ring patch.
C. HFSS Software
HFSS is a high performance full wave electromagnetic (EM) field simulator for arbitrary 3D volumetric passive device modeling that takes advantage of the familiar Microsoft Windows graphical user interface. Ansoft HFSS employs the Finite Element Method (FEM), adaptive meshing, and brilliant graphics to give unparalleled performance and insight to all of your 3D EM problems.

According to the parameters shown in Table I, antenna model is designed in HFSS software and simulated. Fig. 2 shows model design of proposed antenna. Fig. 3 gives Reflection Coefficient (< -10dB) having impedance bandwidth of about 170MHz for GPS and about 100MHz for Bluetooth application. Fig. 4 shows VSWR which is 1.52 at 1.58GHz (GPS) and 1.67 at 2.4GHz (Bluetooth), both values are well within limiting values of VSWR i.e. 1 and 2. Fig. 5 shows Radiation pattern, which shows only one main lobe and one side lobe. This main lobe indicates that our antenna radiates in single direction i.e. our antenna is unidirectional. Fig. 2 Software Model Design in HFSS Fig. 3 Reflection Coefficient of Proposed Antenna Fig. 4 VSWR of Proposed Antenna Fig. 5 Radiation Pattern of Proposed Antenna IV. CONCLUSION Design of new coplanar, multifunctional, dual band antenna for GPS and Bluetooth application with appropriate pattern and polarization is described in this paper. Microstrip line feeding is used to feed square ring patch antenna without affecting operation of inner square patch. It generates required right handed circular polarization for GPS application. Besides this outer square ring patch is also used to load inner square patch with vertical liner polarization for Bluetooth application. Thus highly unidirectional, wide-band antenna is designed whose VSWR is within permissible limits but it can be improved further. The hardware results were found to agree very well with simulated results. ACKNOWLEDGMENT The authors would like to thank the RIT Institute for the timely and important help in the field of electromagnetic. The authors also wish to thank the reviewers for their very detailed review of the manuscript and for their help in clarifying some aspects of the reported results.

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