Wideband Directional Microstrip Antennas fed by CPW-loopCombination

Nasimuddin and Zhi Ning Chen

Institute for Infocomm Research, 20 Singapore Science Park Road, #02-21/25, Science Park II, Singapore117674, Email: nasimuddin@ i2r.a-star.edu. chenzn@ 2r.a-star.ed

Abstract - A new coplanar waveguide (CPW)-loop offers the advantage of easy integration with active devicescombination feed wideband directional and compact multilayer due to their uni-planar design, eliminating the need for vias. Inmicrostrip antenna is presented for UWB applications. The the literature, some of feeding methods for single layerantenna consists of two dielectric layers; CPW-loop on the . ' i. .ground plane, main patch on the middle layer and four cosp aing CPW mly iuve orecpaItIveasymmetric parasitic patches on the upper layer. The feed coupling via a rectangular slot have been explored [11].consists of a CPW structure and a loop on a ground plane. The Furthermore, since the CPW conductors are also used as theantenna has a measured 10dB return loss bandwidth of 36% ground plane for the microstrip patch, the feed substrate used(3.12GHz to 4.51GHz) and maximum gain more than 5dBi over in conventional microstrip aperture coupling is no longerthe 48% (3.0GHz to 4.90GHz). The total thickness of antennas is4.65 mm. The proposed technique is very useful for designing needed.wide bandwidth antennas on multilayer printed circuit board. In this paper, we propose a new type of directional

Index Terms - CPW feed, loop coupled, multilayer dielectric wideband and compact multilayer microstrip antenna feed bylayers, UWB, wideband, microstrip antennas. CPW-loop combination for UWB applications. The antenna is

consists of main and four asymmetric parasitic patches. Thefeeding structure is consists CPW and combined with loop.

I. INTRODUCTION The prototype antenna was fabricated and its return loss wasIn recent years, there is an increasing demand to integrate measured. We achieved very good agreement with measuredplanar antennas into three-dimensional packages as well as return loss and simulated return loss by IE3D simulator. Thedesigning antennas on multilayer laminates, which pose as a antenna was designed by using the method of moment basedchallenge, especially to ultra-wideband (UVvB) antenna electromagnetic solver IE3D.design. The multilayer microstrip directional antenna fed by acoplanar waveguide has the advantages of easy massproduction and lower antenna assembling cost. Moreover, theuse of coplanar waveguide feed is more suitable for The proposed wideband directional and compact multilayerintegration with circuit devices and design of antenna array microstrip antenna with asymmetric parasitic patches fedcompared to other exciting feeding structures. CPW-fed through the CPW-loop combinations electromagneticallymicrostrip antennas have been widely used for various coupled is shown in Fig. 1(a). It consists of two dielectricapplications because they are compatible with monolithic layers; the CPW-loop printed on ground plane, the main patchmicrowave integrated circuits (MMICs) and active devices fabricated on the lower dielectric substrate (Layer#l, hl, C,)[1]. In addition, the bandwidth of CPW-fed microstrip and the asymmetric parasitic patches are printed on upperantennas is larger than conventional microstrip antennas [2]. dielectric substrate (Layer#2, h2, y,2). The top view of allTraditional feeding techniques include the use of direct feed conducting layers as well as ground plane is shown in Fig.[3], electromagnetically coupled [4, 5], aperture coupled 1(b).microstrip line [6, 7], coaxial probes [8] and coplanar Asymetficwaveguides (CPW) [9]. The directional and wideband antcsiicpatmicrostrip antennas are very important for high data ratetransmission of UWB applications. The technology promiseshigh-speed transmission rate for short-range, indoor datacommunications. In 2002, the Federal CommunicationsCommission (FCC) allocated the spectrum from 3.1 to 10.6GHz for unlicensed UVvTB measurement, medical andcommunication applications [10], which have prompteddevelopment of antennas and systems capable of covering the Groundplane C:PW-Loop Groundplanecomplete UWB frequency band. The multilayer directionalantenna for UWB applications fed by CPW can be easily Fig. 1(a). Cross-section of CPW-loop combination feed widebandintegrated on the multilayer circuit devices. Using CPW also multilayer microstrip antenna.

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P29( L2 > The CPW-loop combination fed is electromagneticallycoupled to the driven patch. The asymmetric parasitic patchhas been used to improve the impedance bandwidth and gainover the impedance bandwidth. The main patch (P1) on layer

f l i d t d4#1 with length, LI= 16.0mm and width WI = 19.0mm. In orderto improve the impedance bandwidth and gain over theimpedance bandwidth we have used asymmetrical parasiticpatches on layer #2. We have used four parasitic patches such

3- i\ sas P2, P3, P4 and P5. The P2 and P4 are same as well as P3 andP5 are also same as shown in Fig. 1(b). The P2 dimensions:

_IL3 width (W2) is 19.0mm and length (L2) is 20.0mm and P3_ ~ X _dimensions: it is square patch with area (L3 x L3) of 16.0 mm

x 16.0 mm. The distance between the centers of the parasitic. 3 patches are d, = 3.0 mm, d2 = 4.0 mm, d3 = 4.0 mm and d4 =

2.0 mm as shown in Fig. l(b). Loop dimensions: inner(LinxL1) is 16.0 mm x 16.0 mm and outer (Lox Lo) is

Li 17.0mmx17.0mm. CPW line width (W) is 8.0mm and gap (G)is 0.5mm. The CPW stub length (s) is 0.5mm. This help toimprove the impedance matching of antenna. Ground planesize is 60mmx60mm. The lower substrate (Rogers) is h, =1.524 mm, Fr, = 3.38, tan6I = 0.0027 and upper substrate(Taconic) is h2 = 3.124 mm, Cr2 = 3.254, tan6I = 0.003.

II. PROTOTYPE ANTENNA

The proposed optimized antenna was fabricated. Thefabricated prototype antenna is shown in Fig. 2. The CPW-loop combination feed and driven microstrip patch wasfabricated on layer#1 (Rogers R04003). The asymmetricparasitic patches were etched on layer#2 (Taconic C-32). Thelayer #1 and 2 tightened together using plastic screws. Theimpedance matching performance of the antennas wasmeasured using an Agilent vector network analyzer N5230AL. \I and the radiation performance was measured using theMIDAS far-field measurement system.

N

Fig. 1(b). All layers top view of wide bandwidth multilayerFmicrostrip antenma.

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III. RESULTS AND DISCUSSIONS IV. Conclusion

The measured and simulated return loss of the antenna is A new compact and directional multilayer microstrippresented in Fig. 3. The measured lOdB return loss bandwidth antenna fed by CPW-loop combination has been presented foris around 36% (3.12GHz to 4.51GHz) and simulated UWB applications. The return loss and radiation patterns ofbandwidth is around 36.8% (3.10GHz to 4.50GHz). The antennas have been measured and presented. Good agreementmeasured VSWR < 2 impedance bandwidth is around 45.5% between the measured and theoretical results has been(3.11 GHz to 4.96 GHz) which is suitable for lower frequency observed. These antennas can be used for UWB high-data rateband of UWB applications. A very good agreement is indoor meshing communications and UWB low-data rateachieved between the simulated and measured return loss. indoor location requester applications.However, there is a little shift at higher frequency band asshown in Fig. 3. Fig. 4 shows the measured and simulatedmaximum gain of antenna. The maximum gain of 8.5 dBi was ACKNOWLEDGEMENTmeasured at 4.75 GHz and it is more than 5 dBi over the 48% The authors would like to thank Dr Wee Kian Toh,(3.0 GHz to 4.90GHz). Xianming Qing and Terence S. P. See for his assistance and

insight to this research work. We also thank Taconic foro supplying us free samples of their dielectric materials.

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3 3.5 4 4.5 5

Frequency (GHz)

Fig. 4. Measured and simulated maximum gain of antenna.

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