Proceedings CEEM'2009/Xi'an

A planar monopole antenna design for UWB applications

AND

y

Lz

-

DESIGN

L

Figure 1 Geometry of the proposed antenna

2. ANTENNAANALYSIS

Figure 1 shows the geometry of theproposed antenna. The circular patch isprinted on a dielectric substrate with relative

Min Zhang, Xin-Huai Wang, Xiao-Wei Shi, Chang-Yun Cui, and Bin WuNational key Laboratory ofAntennas and Microwave Technology

Xidian University

Xi'an, 710071 , P. R. China

Corresponding author: zmfun@qq.com

Abstract: A planar antenna is designed for structure planar antennas have been presentedultra-wideband applications in this paper. A such as the Vivaldi tapered slot antenna [2],circular patch as a radiating element printed printed elliptical monopole antenna [3], andon a dielectric substrate with relative several round, rectangle and ladder shapepermittivity of 2.65, thickness of lmm, and antennas [4]. Planar printed antenna [5-7] hasfed by a 50 n microstrip line. A gradual been one of the focuses of interest in recentchanging structure is designed in the bottom years for its plane structure, fabricationof the floor to improve the impedance simplicity, high radiation efficiency and easybandwidth. Simulated and tested results show integration.the proposed antenna can meet theultra-wideband (UWB) bandwidthrequirement of3.l-1O.6GHz. The antenna hasa steady-state gain,and omni-directionalradiation patterns among the workingfrequency.Key words: UWB, planar monopole antenna,gradual changing structure.

With the development of the indoor highspeed wireless access technology, UWB shortdistance wireless communication technologyhas attracted more and more attention in thefield of wireless communications. As animportant part of the UWB system, UWBantenna becomes a hot research topic in recentyears [1]. The main requirements of the UWBantenna design include impedance matching,steady-state gain, and good radiationperformance over the entire frequency range(3.1-1O.6GHz). Since 1970's, a lot of simple

1. INTRODUCTION

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2.2. Radiation PatternsThe simulated radiation patterns for theproposed antenna are shown in Figure 4.Because of the limitation of the testequipment and time, radiation pattern has notbeen measured. However, we have analyzedthe simulated results. It is shown in Figure 4that the proposed antenna has relativelyomni-directional x-z plane (H-plane)radiation patterns. The radiation patterns aresimilar over the whole operating frequency.

(a)

Figure 3 demonstrates the simulated returnloss curves for different value of Ld. Figure 3shows that the first resonant frequencydecreases with the increase ofLdand with thevalue of Ld = 6.4 mm the operationbandwidth obtained. Dimensions areoptimized based on numerical results andshowed in Table 1.

L W LJ Ld WJ wJ R R J H

35 25 7.9 6.4 8.5 1.9 14 20 1

Table 1 Antenna Dimensions in Millimeters

..-

~ .10 \ I/~~SI"\\-/ !__

;Ir.······L,5.5mml·20 • ! ... L/.5mm!

"i l==_~f:~~1

permittivity of 2.65, dimensions of Lx W ,

thickness of 1 mm, and fed by a50 n microstrip line. A gradual changingstructure is designed in the bottom ofthe floorto improve the impedance bandwidth.

.5.------ - - - - - --,

Figure 2 Simulated return loss for theproposed antenna in terms of W]

.5.--- - - - - - - - - - -,

2.1. The Effect ofthe Antenna Dimension

Width Wfof the metal conduction strip affectsboth the lower band and the high frequency.Figure 2 demonstrates the simulated returnloss curves for different value of W]. It isseen in Figure 2 that the simulated return lossdecreases with the increase of W]at the lowerband and showing an opposite result at thehigh frequency.

6 7 8 10

Frequency (GHz)

6 a '0

Frequency (GHz)

Figure 3 Simulated return loss for theproposed antenna in terms ofLd

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(b)

(c)Figure 4 Simulated radiation patterns fordifferent frequencies (a) y-z plane; (b) x-yplane; (c) x-z plane

3. RESULTS

To verify the validity, the proposed antenna isfabricated on a PTFE substrate with relativedielectric constant of 2.65 and thickness h= 1mm. Figure 5 shows the photograph of thefabricated antenna.

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(a)

(b)Figure 5 Photograph of the proposed antenna

(a) the front face of the antenna; (b) thebottom face of the antenna

The return loss of the antenna is measuredby Agilent N5230A. Figure 6 shows thesimulated and measured return loss of thisantenna.

-0- SII Simulated- . - SII Measured

·25

6 T 8 W

Frequency (GHz)

Figure 6 Measured and simulated return loss

Proceedings

The return loss was less than -10dB from3.1r-.JI0.6GHz with one resonance in theoperating bandwidth close to 4.4 GHz. Theground plane is regarded to an impedancematching circuit with a good impedancematching in a wider frequency band. And thegradual changing structure can makefrequency resonance mode of the antennaachieve gentle transition from one to anotherand improve the impedancebandwidth effectively.

The measurement result has a goodagreement with the simulation. The deviationbetween the two was mainly due tonon-uniform dielectric medium plate, theantenna size of the error processing, 5MBwelding joints as well as environmentalfactors. Those deviations are in the range ofacceptable.

4. CONCLUSIONS

In this article, a planar antenna is designed forhigh rate, shout-rang wireless communication.The proposed antenna is suitable for UWBsystem over the entire frequency range.Results of impedance bandwidth and radiationcharacteristics are given. The measurementresult has good agreement with the simulation.The antenna is a good candidate for UWBapplications due to its compact structure, easyintegration, low cost, easy processing etc.Future work consists of design analysis andimplementation ofband-notch ultra-widebandantenna.

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Planar miniature tapered-slot-fed annularslot antennas for ultra-wideband radios,IEEE Transactions on Antennas andPropagation, v53, n3, 2005,

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pp:1194-1202.2. Guillanton E, Dauvignac JY., Pichot

C, Cashman J, A new design tapered slotantenna for ultra-wideband applications,Microwave and Optical TechnologyLetters, Vd.19, n04, Nov. 1998,pp:286-2899.

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