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Progress In Electromagnetics Research Symposium Proceedings, KL, MALAYSIA, March 2730, 2012 57

Dual Band Microstrip Antenna Working in the Frequency Bands

2.4 GHz and 5.8 GHz

R. Przesmycki, M. Wnuk, L. Nowosielski, K. Piwowarczyk, and M. BugajFaculty of Electronics, Military University of Technology

Gen. S. Kaliskiego 2 Str., Warsaw 0-908, Poland

Abstract The fast development technology of wireless internet access and the requirementsto comply of the standards applied to the WLAN (Wireless Local Area Network) as well asthe possibility of using the ISM (Industrial, Scientific, Medical) frequency bands in the ranges24002500MHz and 57255875 MHz has forced demand for dual-band antennas, which can beimplemented in stationary and mobile devices. The paper shows the dimensional model of theantenna made in microstrip technology, working in two frequency bands 2.4 GHz and 5.8 GHz.This antenna can be used in mobile wireless networks. The paper show the results of simulationof radiation characteristics and electrical parameters of designed antenna made in the softwareCST Microwave Studio and the measurement results performed in anechoic chamber in the Elec-tromagnetic Compatibility Laboratory in Military University of Technology in Warsaw, Poland.

1. INTRODUCTION

The fast development technology of wireless internet access and the requirements to comply of thestandards applied to the WLAN (Wireless Local Area Network) as well as the possibility of usingthe ISM (Industrial, Scientific, Medical) frequency bands in the ranges 24002500 MHz and 57255875MHz has forced demand for dual-band antennas, which can be implemented in stationaryand mobile devices. Using antennas in mobile devices provides to requirement for unidirectionalradiation patterns. This requirement, and additionally requirements on the size and electricalparameters of antenna meets mostly built antenna in microstrip technology.

One of the ways implementation of dual-band microstrip antenna is a double T antenna, whichcomposed of two radiators in the shape of the letter T. In most of solutions radiating elementshave different sizes. This allows antenna can work in two frequency bands. One of the waysimplementation of dual-band microstrip antenna is a double T antenna, which composed of tworadiators in the shape of the letter T. The double T antenna can be considered as two parts placed

on one side of the laminate. They are supplied 50 microstrip line placed on the same side of thelaminate. On the second side dielectric is a ground plane (Figure 1(a)). One radiating elementof antenna is operating in the lower frequency band. The second radiating element is designedfor higher frequency band. Using different lengths of the horizontal line, and the thickness of theradiating elements allows for wider frequency bandwidth [2].

Double T antenna can be analyzed as two separate antennas working on individual frequencyband.

Other interesting solution of dual band antenna is a structure which showed in Figure 1(b). Theconstruction of this type antenna allows for a much larger frequency bandwidth than the antennawhich is presented in Figure 1(a) [1].

2. THE MODEL AND SIMULATION RESULT OF DESIGNED ANTENNA

Figure 2 shows the analyzed antenna. It consists of two /4 monopolies shaped in T letter. Eachof the two monopoles consists of two parts, orthogonal with each other. Element responsible for

(a) (b)

Figure 1: Models of double T microstrip antenna.

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the upper frequency range is a radiator in a T letter shaped, located in the central part of theantenna, while the radiator is responsible for the lower frequency range (2.4 GHz) is located above.Using the simulation environment CST Microwave Suite, model of antenna was created, whosegeometrical dimensions are shown in Figure 2.

As a result of the design process were finally selected dielectric: h2 = 1.524 mm, 2 = 2.6 Rogers RT/ULTRALAM 2000.

Geometrical dimensions of the antenna shall be set at: Wg = 72.98mm, Lg = 29mm, Lde =

24.33mm, Wf = 4.83mm, Htu = 16.06mm, Htl = 9.245 mm, Ltu = 5.15mm, Wtu = Wtl =1.94mm, Ltl = 7.26 mm. For this model of the antenna using a simulation environment CST,electrical parameters and radiation patterns of the antenna was determined. Figure 3 shows thecourse of the VSWR and the antenna input impedance.

Figures 4 and 5 shows a radiation patterns of the antenna model in two polarization for 2.4 GHzand 5.8 GHz frequency obtained by the simulation. In the vertical polarization for both the fre-quency characteristics of the antenna are omnidirectional, which agrees with the assumptions poseddesign for the prepared antenna. The real part of input resistance of the designed model antennafor frequency 2.4 GHz is 39 while for the frequency 5.8 GHz is 46 (Figure 3(b)).

(a) (b)

Figure 2: The dimensioned model of analyzed antenna: (a) Construction of the radiator. (b) General view.

(a) (b)

Figure 3: (a) The simulation course of VSWR and (b) real part of input impedance as a function of frequency.

(a) (b)

Figure 4: The simulation of radiation patterns of thedesigned antenna model for vertical polarization forthe frequency: (a) 2.4 GHz. (b) 5.8 GHz.

(a) (b)

Figure 5: The simulation of radiation patterns of thedesigned antenna model for horizontal polarizationfor the frequency: (a) 2.4 GHz. (b) 5.8 GHz.

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Figure 6: Double T antenna during the measurements in anechoic chamber.

PERSONAL COMPUTER

PC

WITH SOFTWARE

RECIVER HP 8530

WITH

SOFTWARE HP 8510

GENERATOR

HP 83620

FREQUENCYCONVERTER

HP 8514

(S-PARAMETER TEST SET) ANTENNATEST

KALIBRATOR

HP85060C

(ECal Unit)

Calibration module

HP 85062-60001 lub

HP 85062-60002

MANUAL

CALIBRATION

KIT

GP-IBBUS

SWEEPIN

STOP

SWEEP

GP-IB

IFINTERCONNECT

Figure 7: Block diagram of measuring position for VSWR testing and input impedance of antennas.

Czstotliwo [MHz]

7000650060005500500045004000350030002500200015001000

WFS

10

9

8

7

6

5

4

3

2

1

Czstotliwo [MHz]7000650060005500500045004000350030002500200015001000

100908070605040302010

0

Czstotliwo [MHz]

7000650060005500500045004000350030002500200015001000

X[ohm]

10080604020

0-20-40-60-80

R[Ohm]

(a) (b)

Figure 8: (a) The measured course of VSWR and (b) input impedance (real and imaginary part) as afunction of frequency.

3. THE MEASUREMENT RESULTS OF ELECTRICAL PARAMETERS AND

RADIATION PATTERNS OF DOUBLE T ANTENNAFor the validate the analysis performed in the previous chapter, and verify the electrical parametersobtained in the final simulation model of the antenna were measured for the antenna made aphysical model based on the results of the simulation. Figure 6 shows a designed model of doubleT antenna placed in the right place at the measurement positions of the radiation patterns andVSWR measurements in the anechoic chamber.

For measuring SWR and input impedance of antennas it is necessary to draw up measuringposition in the configuration showed in Figure 7.

Measurement of VSWR and input impedance requires conducting calibration of measuring po-sition. Calibration allows to minimize systematic errors which could appear during measurements.Because for SWR measurements and input impedance for various types of antennas there can beused different kinds of ducts, it is calibration that will provide elimination of influence of theirparameters on the measurement result. After performing calibration of measuring position and

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verification of correctness of the performed calibration, to slotted line in the place of matched loadit is necessary to connect the tested antenna. Connection should be made in such a way thatmeasuring cable is connected directly to antenna input or by using minimum essential number ofadapters necessary for change of connection standard.

Due to frequency band in which designed microstrip antenna operate, the measurements havebeen conducted in the range from 2 GHz to 6.4 GHz. The measurement results of VSWR andinput impedance (real and imaginary part) of the discussed microstrip antenna in the function of

frequency are showed in Figure 8.Obtained by measuring the input resistance value is 39 for a frequency 2.4 GHz and 39 for

a frequency 5.8 GHz (Figure 8).For measuring antenna patterns it is necessary to draw up measuring position in the configura-

tion shown in Figure 9.Measuring of antenna patterns is performed in the below mentioned way. For initial position

of rotary head desired power in the generator output is set and the first measuring frequency.Measurement of the power level of reference signal is conducted as well as test signal received bythe tested antenna. After finishing measurement there comes retuning of the signal source andmeasuring both signals for next declared frequency. These measurements are carried out in turnuntil the last assigned frequency. According to the assigned step, rotary head performs rotationof the tested antenna to the next angular position and stops. Finishing measurements takes placeafter measuring power levels for the whole full rotation angle of the tested antenna.

On the basis of VSWR results and input impedance of the discussed microstrip antenna, themeasurements of antenna characteristics have been made in the range of frequency of operatingband of antennas, taking into account edges of frequency interval of operating band of antenna andmind-band frequencies. The measurement results of the discussed microstrip antennas in the angle

HP 8511

Transmit

AntennaReciver

Antenna

Transient Panel

Generator

Power

Amplifier

MICROWAVEBOARD

Ref. OUT

Input

Amp. IN

Amp. OUT

Output

ANECHOIC

CHAMBER

MEASUREMENT

ROOM

Figure 9: Block diagram of measuring position for antenna patterns measurements.

(a) (b)

Figure 10: Normalized antenna patterns of double Tantenna in vertical polarization for frequencies: (a)2400 MHz. (b) 5800 MHz.

(a) (b)

Figure 11: Normalized antenna patterns of doubleT antenna in horizontal polarization for frequencies:(a) 2400 MHz. (b) 5800 MHz.

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function for selected frequencies of the whole operating band are practically identical. Becauseof that, below there are presented normalized characteristics of the discussed microstrip antennafor the selected frequencies 2.4 GHz and 5.8 MHz in polar coordinates in vertical polarization (Fig-ure 10) and horizontal polarization (Figure 11).

These results confirm the radiation patterns are omnidirectional shape in the vertical polariza-tion, which is an advantage as an designed antenna for the possibility of using an designed antennain mobile devices.

4. CONCLUSION

After analyzing the measurement results of the discussed microstrip antennas we can state thatpresented antennas are characterized by good mechanical and electrical parameters. Depending onneeds, particular antennas can be used in various fields. The form of radiation characteristics is inaccordance with theoretical assumptions.

The presented double T antenna model gives the possibility to work at the same time over theWi-Fi 2.4 GHz and ISM frequencies from the range 24002500MHz and 57255875 MHz range. Theconstruction of the designed antenna made a modern solution to an antenna device for a compactform, which is especially important in a situation to use it on mobile devices. Omnidirectionalradiation pattern in the plane of vertical polarization additionally increases usability of the designeddouble T antenna.

ACKNOWLEDGMENT

The research work financed from the financial funds assigned to the science in the years 2011/2013as the development work. The research work is realized in Poland.

REFERENCES

1. Jang Large, Y.-W., Bandwidth double-T shaped microstrip fed single layer single slot an-tenna, Microwave and Optical Technology Letters, Vol. 30, No. 3, Aug. 5, 2001.

2. Kuo, Y.-L. and K.-L. Wong, Printed double-T monopole antenna for 2.4/5.2GHz dual-band WLAN operations, IEEE Transactions on Antennas and Propagation, Vol. 51, No. 9,Sep. 2003.

3. Wnuk, M., R. Przesmycki, L. Nowosielski, and M. Bugaj, Multilayer microstrip antenna onflat base in the X band (8.5 GHz12GHz), PIERS Online, Vol. 7, No. 3, 216220, 2011.

4. Bugaj, M., R. Przesmycki, L. Nowosielski, and K. Piwowarczyk, Active microstrip antennasoperating in X band, PIERS Online, Vol. 7, No. 3, 221225, 2011.