2002 Student Conference on Research and Development Proceedings. Shah Alam, Malaysia

XOR.WW2

ANALYZING AND DESIGNING OF A DUAL BAND ACTIVE ANTENNAS

Rosli Omar and Syed Idris Syed Hassan

School of Electrical and Electronic Engineering Universip Science Malaysin, 14300,Nibong Tebal

Seberang Perai,Pulau Pinang, W. Malaysia rosli@eng.usm.my syed@eng.usm. my

Abstrucf: A study has been done for analyzing and designing of ,a dual band active antennas.Dual band is accomplishing' by , combinating of two forms of helicalantennas,i.e cylindrical' and conical.The antenna has a resonant frequency of 860 MHz and 1800 MHz based on IMT-2000. An empirical equations has been suggested to calculate resonant frequency o f ' the antennah this paper discuss also include the design four-port circulator for resonant frequency of 2GHz.This circulator hasbeen used to isolate transmit and receive signals by using the same antennas. The gain of dual band antennas was amplified by using MGA-86563 amplifier of . Hewlett , Packard's product. Hewlett Packard's -MGA 86563 is MMIC (Monolithic and Microwave. Integrated Circuits) that offers low noise figure and excellence gain so that this antenna can acts as active antenna.Using MMIC technique, circulator and amplifierkin be combined together and will reduce to a small .size which is, suitable for any mobile communication systems.

Keywords Antenna. normal mode helical an:enna. resonant frequency.

1. INTRODUCTION

Normal Mode Helical Antenna (NMHA) is normally used for mobile communication such as walkie-talkie, mobile telephone etc. This is mainly due to its small size. flexibility,considerably unbreakable structure and suitable input impedance nearly to 50 ohm.

The important design parameters for helical antenna are the diameter D, circumference C, separation between turns s, pitch angle a, and the number of turns N [1,2,3]. There are two practical modes of radiation. The first mode is called normal mode whereby the radiation is normal to the antenna axis. For this mode the antenna is designed in such a way that the circumference C , and the separation s should be less 0.5 of a wavelength [1,2,3]. The second mode is called the axial mode whereby the radiation is along the antenna axis. In order

to'operate in this mode the antenna must be designed in such a way that the separation s is less than 0.5 of the wavelength and the circumference C is between 0.75 and 1.25 ofa wavelength [1,2,3,4]

Its characteristics, especially resonant frequency depends on the configuration of its physical parameters. Several experiments using different values of physical parameter were done to study the variation of resonant frequency of the two form of helical antenna over its physical parameter .The combination of antenna will results in a dual band antenna. The design of. circulator and amplifier are also discussed. ~ .. .

2. DESIGNING NORMAL MODE CYLINDRICAL HELICAL ANTENNA FOR RESONANT

FREQUENCY FROM COOMHZ TO 3GHZ.

Several experiments [3] observations suggest relationship between, resonant frequency is inversely proportional with its physical parameters;

f , aN" DLY S/

Where:

& = resonant frequency (Hz) N = number of turn Dh = cylindrical helical diameter S, = separation between turn

Since the frequency characteristics of cylindrical NMHA depend on its three physical parameters (N, Dh and S,), therefore it is easy to do analysis on resonant frequency of NMHA by choosing any two of these physical parameters as control variables.

0-7803 -7 5 6 5 -3/02/$17.00 02002 IEEE. 136

2.1. RESULT AND DISCUSSION

Fig. 1 shows that linear regression analysis of resonant frequency fo of cylindrical NMHA versus number of turn with several diameter Dh values. In Fig.2 shows that linear analysis of resonant frequency fo versus antenna diameter Dh with various N values,and in Fig.3 shows that linear analysis of resonant frequency fo versus Helical antenna separation S, with several values of N.

All regression equations in Fig. 1 to Fig. 3 are summarized in Table 1 to Table 3. Each table has three columns, i.e value of regression equation and column of residual square (R'). From the RZ we observed that all values are close to 1. In other word these values imply that all regression equations in second column give good representation to all measured data.

NunkrofTurn N

0 5 10 15 20 25

Number of Turn ( N )

Fig. 1 Curve off, venus N with several DI valuer for S, = 0.5 cm

Regnsilan equlHm Rerldul square G-KO (R*1

- . 0 0.5 1 1.5 2 2.5

Cylindrical Helical Antena Diameter (Dh)

F1g. I Curve 0% Venus D. with several values of N for $ = 0 . h

0 0 5 1 1 5

separation between turn sp (spsm)

Fig.3 Curve off, versus S, with several N for Dh = 0.8 cm

I I I I ""I. 1 l ,..-.."'"" Y.7,. I

I I &-3.1751W 0.994 1 [ &-2.8900W I 0.9891

" --

Table 2 Regression equationf, versus Diameter Dh with several values of N.

Table 3 Regression equationf, versus S, with several values of N

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3. DESIGNING NORMAL MODE CONICAL HELICAL

K = 4 4213NoSo2'

R2 =0.998 c

0 5 10 15 20 25

Number of tum( N )

Fig.4 Curve of Constant Kversus N

' . " ,

0 0.5 1 1.5 2 2.5 Antena Diameter (Dh,cm)

Fig5 Curve of Constant K versus Dh

0 0.5 1 1.5 2

Separation between turn(Sp,cm)

Fig.6 Curve of Constant K versus S,

In the second column of all tables (table 1 to table 3) ,we may plot the constant K versus N,Dh and S, as shown in fig.4 to fig.6.The relationship between/,,NDh andS,can be expressed in power form equation or (regression equation as shown below;

, .

K - - h NU 5024~~0.8163 0.3702 SP

(2) From measurement we have, J.=2GHz;iV=3, Dh=0.8cm and S,=O.Scm.By substituting all these values into equation (2)_the constant K is obtained to be 2.24.

Finally, equation (1) can be completed as follow;

(3) wherefo is resonant frequency (Hz), constant 2.24 is in Hzm, N is number of turn, D is diameter of helix (cm) and S, is Antenna separation between turn (cm).

ANTENNA FOR RESONANT FREQUENCY FROM B O O M H Z TO 3GHZ

An empirical equation for resonant frequency of normal mode conical helical antenna has been suggested;

h a IV"O,-~S;' (3) Where:

h = resonant frequency (Hz) N = number of turn Dh= antenna diameter or 6, = pitch angle conical helical S, = separation between turn

Resonant frequency of conical NMHA depends on its three physical parameters (N, 8, and S,). Several experiments using different values of physical parameter were done to study the variation of resonant frequency over its physical parameter [4].

3.1 RESULT AND DISCUSSION

3000 4 2500

- P 3 2000 P.l.l*.lO1....l-.C...,,

i 1500 E

e 500 5: L 0

c ..I/*-"U...IY-*m..I,

U

1000 .. c

0 5 10 15 20 25

Number of Turn (N)

Fig. 7 Curve off0 versus N with several values of Dh

0 4 I 0 2 4 6 6

Pitch Angles in degree

Fig. 8 Curve off0 versus eh with several values of N

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1 0

Pitch Angle eho

7.59

7.11

6.81

6.65

6.51

6.41

5.71

..89

0 . 0.5 1 1.5 2 2 5 Separation between Turn (Sp, cm)

Regmslon Eguation Residual Square V.=KK4 1 CR')

/..*5(s11=- 0.9943 fi3.513&Dnn 0.9817

I..6.0M&a"Y 0.9901 .

/~6.5W*.~""' 0.9778

I.=L.7.04-=- 0.9906

*.7.17111*- 0.993

I..9.kS04°J'd 0.9995

f~ I3 .40 IA 0.9981

Sepmlion Regression equation between U.=KSP?

Table 6.Regression equationf, versus S, with several

Residual Square @*)

I

1

0 0 5 10 15

Number of turn N

Fig 10. Curve of Constant " K versus number of turn (N )

0 2 4 6. 8

Pitch angle in degree

Fig 11. Curve of Constant " K versus pitch angle ( 61, )

2 5 , I

0.5

0 0.5 1 1.5 2 2.5 Separation between tum (Sp,cm)

Fig 12:Curve of Constant "K" versus separation between turn ( S, )

In fig.7 to fig.9 show that linear regression has been used to analyze resonant frequency versus N, S, and S,. All regression equations obtained in entire figures are summarized in table 4 to table 6. From the entire tables, the values of Rz is closed to 1.These values imply that all regression equations give g o d representation to all measured data. The values of constant a, b and c can be determined from fig.10 to fig.12 which considered as average value. The relationship between N 4 and S,, can be expressed in power form equation as shown below;

(4) Now ,the value of K can be calculated by substituting5 = 2GHz. N=3 Dh=0.8cm and SP=0.5cm. Calculated value ofK is equal 2.32.

Finally,equation ( 4 ) can be completed as follow; x ~o'(Hz) (5 ) 2.32 5=

0, 04'% s, 05802

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Helical

Cvlindrical Helical

Conical

antena

Ground plane

Feed Point Fig. 9 Combination of two.helical antennas .:

Transmined Simal

U Y. Port2 - \ pon4

4 . . . . . . . Fig. iu Rat Race designed.

&I3 Amplifier Circuit ‘Fig.I:14:Combination of Rat

Race and Amplifier Circuit. -

....... ......... :: . ,~: .................. .... .......... ........ :’ i: . ... :, ...... .;

. . . . . . . . . . . . . . .

Fig. 15.Spectrum Pattem.

.’ Fig. 12 Transmitted and received signals

The combination of two helical antennas in cylindrical and conical form has been shown in Fig. 9.Resonant frequency of these two antennas can be calculated easily by using equation (3) and f5). Four-port circulator at resonant frequency 2GHz has been designed as shown in fig. 10. The input from port n will come out at port n + 1 but not out at any another port. If port 1 is the input, then the signal will come out of port 4.110 signal come out of port 2 which is called the isolated port. So this circulator has been used to isolate the transmitted and received signal by using dual band antennas which has been designed.Fig. 12 shows the transmitted and received signals which can operates at both frequencies 860MHz and 1800GHz. To increase the antennas gain, an amplifier circuit has been developed as shown in fig. 13. The combination of amplifier circuit and circulator as shown in fig. 14 would increase the antennas gain. So in this case antennas can acts as an active antenna An output spectrum pattem as shown in fig. 15shows that the gain of antennas has been increased to 10dBm.

4. CONCLUSION

Resonant frequency for dual band active antennas can be calculated based on equations ( 3 ) and ( 5 ). Four 4-port circulator can be used to isolate transmit and receive signals by using the ‘same antennas. The gain of dual band antenna was amplified at 10 a m .

5. REFERENCES

1. Krans, J.D., 1947). “ Antenna New York, Mc Graw-Hill.

Nakano, H, et al. 1986, ‘‘ Axial Mode Antennas and Propagation, Vo;. AF’-34,No.9. 1143-148.

2: ’

3. Simon Ramo,Whinnery,J.R., ~ Van Duzer,T. 1984,”Fields and Waves in Communication Electronics”,John Wiley and Sons Inc.

4. G.H Brown and 0.M.Woodward “Experimentally Determined Radiation Characteristics of conical and Triangles Antena.pp425-455,’ December 1980.

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