reconfigurable beam shaping antenna with wilkinson power divider at 5.8ghz.pdf

8/13/2019 Reconfigurable beam shaping antenna with Wilkinson Power Divider at 5.8GHz.pdf

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2008 IEEE INTERNATIONAL RF AND MICROWAVE CONFERENCE PROCEEDINGS2008 IEEE INTERNATIONAL RF AND MICROWAVE CONFERENCE PROCEEDINGS2008 IEEE INTERNATIONAL RF AND MICROWAVE CONFERENCE PROCEEDINGS2008 IEEE INTERNATIONAL RF AND MICROWAVE CONFERENCE PROCEEDINGS December 2December 2December 2December 2----4, 2008, Kuala Lumpur,MALAYSIA4, 2008, Kuala Lumpur,MALAYSIA4, 2008, Kuala Lumpur,MALAYSIA4, 2008, Kuala Lumpur,MALAYSIA

978-1-4244-2867-0/08/$25.00 2008 IEEE

R F

M 08

Reconfigurable Beam Shaping Antenna with Wilkinson Power Divider at

5.8GHz

M.T. Ali, M.R. Kamarudin, M. N. Md Tan and T. A. Rahman

Wireless Communication Centre (WCC),

Universiti Teknologi Malaysia,Johor, Malaysia.

[email protected], [email protected], [email protected], [email protected].

Abstract -This paper presents a reconfigurable of

multiple element microstrip rectangular linear array

antenna integrated with radio frequency (RF) switches.

The corporate feed design concept is used to excite the

linear array antenna that consists of 8 elements of

rectangular patches at 5.8GHz. Two PIN diode

switches were deployed at the feeding line to activate

the two arrays of patches that is located on the left andright side of the antenna structure.The behavior of thereconfigurable multiple element linear antenna array

system has been investigated with respect to beam

shaping characteristic. The comparisons of the

performance between two structures, with Wilkinson

Power Divider (WPD) and without WPD are discussed

in this paper. Two different beam patterns were

achieved through the reconfigurable antenna at

different number of elements design that incorporates

with PIN diode switches and modified WPD concept.

The simulations and the measurement results for 4 and

8 elements array antenna structure are presented.

Keywords Corporate feed design, radio frequency,

Wilkinson power divider and reconfigurable antenna

1. Introduction

The reconfigurable antennas had drawn lots of

attention in the wireless communication systems

recently. The demand for reconfigurable antenna has

increased drastically since a decade. Reconfigurable

beam shaping is ideal for the detection of small and

large targets at both short and long ranges, includingwhere the antenna is mounted on a high tower or

hillside [1-2]. Reconfigurable antennas are gorgeous

for many military and mobile communication

applications where it is required to have a single

antenna that can be dynamically reconfigured to

transmit or receive on same or multiple frequency

bands [3]. It is advantageous to integrate beam shaping

functionality into the systems so one can vigorously

vary the beam shapes in many applications such as

airplane radar, protection from smart weapons and

point to point communication.

In [4], Rainee N. et al, presented reconfigurable

antennas, which were radiated at different beampatterns by adjusting the apertures and maintaining

their operating frequencies. The antenna presented in

[3], described a dual band dipole antenna integrated

with MEMS switches. However, this method typically

used a dual operating frequency to reconfigure a beam

pattern. The antennas suggested in [5-6], were worked

at dual operating frequencies with a reconfigurable

radiation pattern.

Works done presented in this paper describeand analyze the reconfigurable corporate feed

microstrip patch antenna incorporated with PIN diode

as an RF switch. The switching mechanism is

controlled by the external dc voltage. Two switches are

utilized to realize the antenna with switchable beam

shaping at constant frequency 5.8GHz. The antenna

performances such as input return loss, bandwidth, half

power beamwidth (HPBW), and radiation patterns

were obtained by using Computer Simulation

Technology (CST) Studio Suite 2008.

2. Antenna Design

The configuration of the proposed reconfigurable

antenna structures is shown in Figure 4. There are two

structures of reconfigurable microstrip patch antenna

proposed in this design, without WPD as in structure 1

and added with modified WPD as in structure 2. The

antenna structure was constructed on FR-4 glass epoxy

substrate with a relative permittivity ( r ) of 4.6, loss

tangent () of 0.03 and the thickness of the substrate

is 1.6 mm.

2.1 RF Switching Circuit

Philips PIN diodes, BAP51-02 [7] have been

selected in this design. Figure 1 shows the schematic

diagram of the switching circuit inserted in between

two transmission lines. Each switching circuit consists

of a PIN diode, two DC block capacitors, two

inductors and one resistor. The capacitors, (C1-C2) are

used as DC blocking and the inductors (L1-L2) are

used as RF chokes which provides low impedance for

dc. The biasing voltage (6V) has been connected to

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100 resistor to limit the current flow to the switch.

The simulation results using the PIN diodes equivalent

circuits for the OFF and ON-state are presented in

Figure 2. The return loss is less than -40dB for the ON

state and an approximate of 0dB for the OFF state at

5.8GHz. The selected capacitance and inductancevalues were chosen to be 6.8pF and 22nH,

respectively.

Figure 1: Schematic representation of the switching

circuit components inserted in active feeding network.

Frequency (GHz)

2 3 4 5 6 7 8

dB

-60

-50

-40

-30

-20

-10

0

S11 Switch On

S21 Switch ON

5.8GHz = -49.23dB

5.8GHz = -0.701dB

(a)

Frequency (GHz)

2 3 4 5 6 7 8

dB

-30

-25

-20

-15

-10

-5

0

S11 Switch OFF

S21 Switch OFF

5.8GHz = -18.54dB

5.8GHz = -1.002dB

(b)

Figure 2: Calculated return loss (S11) for ON and OFFstates (a) switch ON mode and (b) switch OFF mode.

2.2 Power Divider Concept

The power divider is one of the most commonly

used components in RF and microwave systems for

power division and/or combination ratio as n-port

network. The ideal design parameters are given inreference [8]. There are two common types of power

dividers used in this antenna design; they are

Wilkinson power divider and T-junction power

divider. Figure 3 shows the structures of a power

divider.

(a) (b)

(c)

Figure 3: (a) Conventional WPD (b) T-junction power

divider and(c) the modified Wilkinson geometry

Wilkinson power dividers with an arbitrary

power ratio was expressed as follows in,[8] .The

modified Wilkinson geometry is shown in Figure 3c. A

4

length of 100 transmission line is connected

between the4 lengths of 50 transmission line.

Another type of power divider used in this paper is T-

junction design [8], shown in Figure 3b, has 50 (Zo)

line input impedances at each port, and a quarter-wave

matching transformer with an impedance of 35.36

(Z1).

2.3 Corporate Feed Patch Array Structure

The PIN diode switches are represented as dotted

black rectangles at S1 and S2 in two locations as

shown in Figure 4. As the size of the switch is 2.5 x 1.4mm, the gap (g) between the transmission lines is

designated as 0.5 mm. In this advance, a dc bias

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circuit is used to control the on/off mode of PIN diode

switches. The beam width can be varied by altering the

number of array elements. When all diodes are on

mode, this antenna basically operates at a concave

pattern of 5.8GHz. In contrast, all diodes are turned

OFF, the antenna element is reduced to four elementswith a convex pattern at a same frequency. The

comparison between the simulations results of the

reflection coefficient of both structures are

demonstrated in Figure 5. Since the return loss for the

structure 2 shown in Figure 5 is much better

compared to structure 1, structure 2 is selected for

the simulation and fabrication purpose.

(a)

(b)

Figure 4: Configuration two structure of corporate fed

reconfigurable antenna array (a) Structure 1 (without

WPD) (b) Structure 2 (with modified WPD).

Frequency (GHz)

5.6 5.8 6.0 6.2 6.4

ReturnLossS

11

(dB)

-35

-30

-25

-20

-15

-10

-5

0

Structure 1

Structure 2 (WPD)

-29.61

-24.49 dB

(a)

Frequency (GHz)

5.6 5.8 6.0 6.2 6.4

Return

Loss,S11

(dB)

-25

-20

-15

-10

-5

0

Structure 1Structure 2 (WPD)-23.56

-16.56

(b)

Figure 5: Comparison of return loss S11(dB) between

antenna structure 1 and 2 (a) 4 elements radiated (b) 8

elements radiated

3. Experimental Result

The antenna described above is fabricated and

tested through simulation and measurement. According

to the simulation results, the radiation pattern

characteristic of the antenna forming has been tuned

efficiently, since its structure is symmetrical by the

center. The pattern obtained is directed to 0. The

radiation patterns of the 4 and 8 elements structure are

shown in Figure 6 and Figure 7 with 3 dB half power

beamwidth (HPBW) of 22 degrees and 12.6 degrees

respectively. Meanwhile the return losses for both

structures are -29.43 dB and -23.56 dB respectively as

shown in Figure 8. Referring to Figure 6(a) and Figure

7(a), it shows clearly that when the numbers ofelements are increased, the beamwidth becomes

narrow with lower sidelobe and high magnitude.

Measurements of reconfigurable beam shaping antenna

was conducted.

The measured return loss compared with the

simulation results for both senses configuration, are

shown in Figure 8. The antenna shows good impedance

matching for both cases which is lower than -20dB

where the return loss is observed. Figure 9, shows the

measurement of return loss when the switches were

turned to ON and OFF-state. The result shows that a

good impedance matching for both cases with -

20.57dB, the return loss is observed at 5.8GHz.The measured radiation patterns, in Figure 10,

show a very good agreement with the simulation. The

results show that two different beam patterns at -3dB,

is about 29o

and 21oat the same frequency. To tune the

frequency from the previous results of return losses for

a good matching, a single open stub is necessary.

Therefore, a single quarter-wavelength open stub,

which operates at 5.8GHz, is added to microstrip

feeding line as shown in Figure 11. Table 1 is the

summary of simulation and measurement results

obtained for the reconfigurable linear array antenna.

S1 S2

S1 S2

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Frequency (Ghz)

4.4 4.6 4.8 5.0 5.2 5.4 5.6 5.8 6.0

ReturnLossS11(

dB)

-40

-30

-20

-10

0

Switch 1 and 2 OFF - 4 patches

Switch 1 and 2 ON - 8 Patches

8 patches antenna

4 patches antenna

At 5.8 GHz

Figure 9: Measured results return loss S11when switchon/off state.

Degree

-100 -50 0 50 100

Am

plitude

-60

-50

-40

-30

-20

-10

0

Measured switches off - 4 patches

Measured switches on - 8 patches

Figure 10: Measured results of normalized radiation

pattern for 4 and 8 patches.

Figure 11: Photo of the fabricated reconfigurable linear

array antenna with single stub matching and PIN diodes.

4. Conclusion

In this paper, experimental data demonstrated the

concepts of reconfigurable number of elements that

produced broad beam and narrow beam radiating

pattern characteristics. By using modified WPD in the

antenna structure, it produced a better performance in

terms of return loss characteristic. This research has

taken advantage of the flexibility of the number of

elements technique by applying it to the problem of

reconfigurable multiple beam array combination. The

reconfigurable dual-beam antenna pattern at fixed

frequencies across the entire 5.7-5.9 GHz band is

presented in this paper with excellent radiation

patterns.

Acknowledgment

The authors would like to thank University of

Technology Malaysia (UTM) for their financial

support to this project. Also our great appreciation to

Wireless Communication Centre (WCC) for providing

all the facilities.

References

[1] Chia-Chan, Chang,Cheng, Liang, Bihe, Deng, Domier,C.Luhmann, N., C., Jr. A beam-shaping phased

antenna array based on true-time delay technologies

Infrared and Millimeter Waves, pp. 99-100, (2002).[2] Madany, Y. M. The analysis of wideband conformalmicrostrip array antenna with cosecant-squared beam

shaping, Radar, 2006 IEEE Conference on, pp. 208-

214,(2006).

[3] Kiriazi, J., Ghali, H., Ragaie, H., Haddara,H.Reconfigurable dual-band dipole antenna on silicon

using series MEMS switches Antennas and

Propagation Society International Symposium, Volume

1, pp. 403-406, (2003).

[4] Rainee N. Simons, Novel On-Wafer Radiation PatternMeasurement Technique for MEMS Actuator Based

Reconfigurable Patch Antennas Glenn Research

Center, Cleveland, Ohio

[5] Yang, F., Xue-Xia, Zhang, Xiaoning, Ye, Rahmat-Samii, Y. Wide-band E-shaped patch antennas for

wireless communications, Antennas and Propagation,

IEEE Transactions on, Volume 49, pp. 1094-1100,

(2001).

[6] Peroulis, D., Sarabandi, K., Katehi, L. P. B., Design ofreconfigurable slot antennas. Antennas and

Propagation, IEEE Transactions on, Volume 53, pp.

645-654, (2005).

[7] BAP51-02_2, Surface Mount RF PIN Switch Diodes,PhillipsTechnologies

[8] J.R. James, P.S. Hall, Handbook of MicrostripAntennas Vol. 2, Peter Peregrinus Ltd., London United

Kingdom, 1989

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