Designing Yagi Antenna

8/10/2019 Designing Yagi Antenna

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Designing Yagi-Uda Antenna Fed by Microstrip Line

and Simulated by HFSSHassan KarbalaeeShahed University

Tehran Iran

[email protected]

Mohammad Reza SalehifarIslamic Azad University

Science and Research Branch

Tehran Iran

[email protected]

Saeed SoleimanyIslamic Azad University

Qazvin Branch

Qazvin - Iran

[email protected]

Abstract- In this article, we have proposed a novel Yagi antenna

that has both compactness of resonant antenna and broadband

characteristics of traveling-wave radiators. It is fabricated on

dielectric substrate with a microstrip (MS) feed. The top layer

consists a microstrip feed, a broadband microstrip-to-coplanar

stripline (CPS) transition and two diopole-elements, one of them

which is driver element is fed by CPS, and the second is director.

The metal underside is a microstrip ground which serves as a

reflector element and cancels using reflector dipole. This antenna

is constructed on low cost substrate with 1.56mm thickness and

.. The simulated bandwidth is about 35% and its gainis more than 5dB.

Keywords: Yagi-Uda antenna, HFSS, microstrip

I. INTRODUCTION

Yagi-Uda first recalls television antenna installed on the roofs.

An example of three elements antenna is shown in Fig.1. Theoptimal spacing in order to maximum directivity (about

15dB) between driver and reflector is about 0.15and the ratebetween driver and director is about 0.25. Generally, thereflector is 5% or more longer than resonant length of driver,

similarly the director is shorter. In General, for antenna with

three or more elements, the driver with a length less than 2 (0.45 0.49) will resonate while the directors length isabout (0.4 0.45). Typically the distance betweendirectors is (0.3 0.4) which is not necessary be similar foroptimal design [1].

II. YAGI ANTENNA BASED ON MICROSTRIP AND COPLANARFEEDING

In order to increase the distance of communications, reducing

interferences coming from other wireless system also toprovide wider bandwidth, the use of printed dipole antenna is

highly recommended [2]. Our antenna schematic which isshown in Fig.2 is designed for performing in UHF band with

about 500~800 MHz bandwidth. Microstrip feeding has this

benefit that the dielectric used in its construction is virtuallya mechanical protective.

Fig.1 Three elements Yagi Uda antenna

A printed dipole (driver) is used in order to create modesurface wave with the least unintended mode that iseffective in Cross-Polarization level determining. In this plan,

the director in addition directs the waves of antenna towards

the endfire direction, simultaneous is involved as a impedancematching element and the groundplane of the microstrip line

on the feeding port of CPS acts as a reflector. Entirely these

cases lead to compression circuit and compatibility with eachMMIC circuit based on microstrip [3].

First, feeding lines and antenna is designed, simulated and

optimized with HFSS software and finally a practical model ismade.

III. MICROSTRIP LINE AND POWER DIVIDER DESIGN

Microstrip line is designed with 50 impedance. There are

specific software to calculate the line parameters such asTX Line, that each calculation methods differ from each other.

Also by referring to microstrip line equations [4], we canseparately achieve these line parameters :

W=2.94mm , 3.13, 84.78In order to convert MS to CPS for feeding antenna is

required transmitted power from 50 line divide between

two50 lines. For this reason we need a impedance

transformer, is shown in Fig.3 .

978-1-4673-1740-5 /12/$31.00 2012 IEEE


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Fig.2 Microstrip Yagi antenna schematic

This is a quarter wave converter for matching 25to 50.By referring to converters formulas [5] :

So transformer characteristic impedance with

4 lengthequal to 35.35 . By referring to [4]:

W=5.08mm

Of course with connecting three 50lines to this transformer,its size needs to resize. In this process, we assumed width and

length transformer as variable elements and set some

parameters of simulation in HFSS as follows :

(width) (length) Solution frequency=2.1GHz

Maximum Number of Passes=15Minimum Number of Passes=3

Minimum Number of Converged Passes=2

0.02New dimensions of simulation are:

5.2 20.2

In Fig.4 S parameter curve is drawn from simulation which

shows the lowest return loss in 2GHz .

IV. 180

DELAY LINE

By using the balun phase shifter to generate a 180 phasedifference between the coupled microstrip lines at the

working frequency, the correct excitation to the antenna is

provided [2]. It is done with selecting proper length for , in Fig.2 such that

4

Fig.3 A. The quarter wave converter with 2 ports

B. The quarter wave converter with 3 ports

This cause odd mode as a dominant mode in coupledmicrostrip line therefore feeding for CPS will be balanced. In

order to the least effect on the phase and amplitude of the

signal in 90bends, we use mitred bends. The distancebetween cut away point and outer corner of the un-mitred

bend is :

y=0.42mmThis value is obtained by using formulas presented in

reference [6].

V. COPLANAR STRIP LINE AND COUPLED MICROSTRIP

Since CPS line dose not accept even mode, playing as opencircuit for even mode of coupled microstirp line and allows us

to negate unintended excited even mode in couple line. 100

line with W=5.17mm andL=0.6mmis calculated by formulaNo.7.

The connected coupled MS to CPS line is designed for 50

characteristic impedance. Based on [7] formula, will beobtained:

W=2.94mm , S=0.6mmCoupled line width is considered as equal as 50 MS line

width because of having the same mitred bends. Fig.5 is

equivalent circuit of odd mode excitation demonstrator.

VI. RADIATOR ELEMENT

Initial dimensions antenna are chosen such as normal yagimentioned in introduction. Main part of antenna , reflector,

which located on back of the board as a finite ground plane,

driver feeding by CPS and director are designed in HFSS. Fora 100 input impedance, the best response for much

bandwidth will be obtained with these dimensions:

5.3, 67.7 5.3, 33.9

19.5, 19, 35.2

VII. RADIATOR ELEMENT

With connecting the feeding part to radiator elements Fig.6

will be obtained. Since this step is the last one in this

simulation and need more accuracy, the type of solution in


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Fig4. Simulated S parameter of power divider

Fig5. Equivalent circuit of odd mode excitation

HFSS is chosen DRIVEN MODE and the antenna will be

located in an air box that really makes radiation boundary;

while the distance between cubic surfaces and antenna is more

than . The input port is LUMPED PORT type with 50characteristic impedance and also INTEGRATION LINE is

drawn from MS line to ground. SOLUTION FREQUENCY isconsidered 2.1GHz for better accuracy. Other parameters are

the same as part III.

After the latest optimization on all of dimensions specially

dimensions of antenna and CPS line to achieve the lowestreturn loss, the following results for antenna dimensions is

obtained that its details are shown in Table 1.

VIII. SIMULATION AND PRACTICAL TEST RESULTS

According to the simulation, the antenna has a bandwidth

( 10about 37% that is shown in Fig.7 . The inputimpedance in Fig.8 shows the antenna in this bandwidth has a

good matching.The antenna patterns in 90, 0planes in Fig.9 andalso the obtained gain from simulation in bandwidth range in

Fig.10 are shown.

As those Figures show, at the center frequency (2GHz) ofbandwidth , gain is 5.4dB and Front to back Ratio is 13dB. Also

Fig11,12 illustrate in HPBW range, Cross Polarization Surface

is lower than -24dB and this is so desirable.

Table 1. Final antenna dimensions based on mm

2.94 0.6 5.2 5.3 22.09 0.6 5.55 67.7 26.75 5.3 2.94 33.9 2.94 5.3 9.78 35.2 9.09 19.5 2.94 19

Fig6. Equivalent circuit of odd mode excitation

Fig7. Simulated Return Loss of Antenna

According to these results, an example of antenna was

made that its measurement results in Fig13,14 shows a little

difference between simulation and reality; the followingreasons can be outlined for this difference:

Using non-professional version of HFSS

Style of connecting the connector and solder


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IX. CONCLUSION

This configuration of printed Yagi-Uda antenna is designedand demonstrated. The optimal dimensions of the antenna are

obtained by HFSS simulation. Even with thicker board by

greater , the dimensions will be shorter. With goodcharacteristics such as wide bandwidth and suitable FTBR,Cross Polarization and gain , it should find wide applications

in wireless systems such as WLANs or GSM. Despite usingonly one director, it has more gain and a wider bandwidth

compared to similar designed antennas. For more gain, adding

parasitic elements to the basic antenna structure or using

antenna arrays is recommended. If we use a printed dipole

with arms in both sides of dielectric substrate in oppositedirections, and feeding by a transmission line, placed on both

sides of the substrate[7][8], the balun phase shifter is deleted

and final antenna size is reduced. Also the gain is increased

but the bandwidth is slightly decreased.

Fig8. Simulated Input Impedance of Antenna

Fig9. Simulated Radiation Pattern

Fig10. Simulated Gain in Bandwidth Range

Fig11. Simulated Radiation Pattern in H plane

Fig12. Simulated Radiation Pattern in E plane


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Fig13. Measured Radiation Pattern for 0

Fig14. Measured Radiation Pattern for 90

X. REFERENCES

[1] Warren L. Stutzman, Gary A. Tiele, Antenna Theory and Design ,

John Wiley & Sons, Inc, 1997.

[2] E. A vila-Navarro, J. A. Carrasco, and C. Reig, Printed dipole antennas

for personal communication systems, ,IETE Technical Review, vol. 27, no.4, pp. 286292, 2010.

[3] W.R.Deal, Noriaki Kaneda, James Sor,Yongxi Qian and T.Itoh, A New

Quasi Yagi Antenna for Planar Active Antenna , IEEE Transactions on

Microwave Theory and Techniques., vol. 48, no.6, June 2000 .[4] Rajeh Mongia, Inder Bahi, Prakash Bhartia, RF and Microwave

Coupled-Line Circuits , Artech House, 1999 .

[5] Peter A.Rizzi, Microwave Engineering , Prentice Hall, 1987.

[6] E.H.Fooks, R.A.Zakarevicius, Microwave Engineering Using Microdtrip

Circuits , Prentice Hall, 1989.[7] A.cheldavi, G. Rezai Rad, Introduction to Electromagnetic

Compatibility , Iran University of Science & Technology, 2004.

[8]E. A vila-Navarro , C. Reig,Directive Microstrip Antennas for SpecificBelow 2.45 GHz Applications , Hindawi Publishing CorporationInternational Journal of Antennas and Propagation ,Volume 2012

Designing Yagi Antenna

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