Reconfigurable Linear Array Antenna with Beam Shaping at 5.8GHz M. T.Ali, T. A. Rahman, M.R. Kamarudin and M. N. Md Tan Wireless Communication Centre (WCC), Universiti Teknologi Malaysia,Johor, Malaysia.
[email protected]
I. INTRODUCTION The reconfigurable antennas have drawn lots of attention in the wireless communication systems recently. The demand for reconfigurable antenna has increased drastically during the past decade. Reconfigurable beam shaping is ideal for the detection of small and large targets at both short and long range, including where the antenna is mounted on a high tower or hillside [1]. 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. The antenna presented in [2], describing a dual band dipole antenna integrated with series MEMS switches. However, this method typically used a dual operating frequency to reconfigure a beam pattern. In [3], the authors presented reconfigurable antennas, that radiated at different beam pattern by adjusted the apertures and maintain their operating frequencies. The antenna suggested in [4] worked at dual frequencies with a reconfigurable radiation pattern. In this paper describes and analyzes the reconfigurable corporate feed microstrip patch antenna incorporated with PIN diode as a RF switches. The switching mechanism is controlled by the external dc voltages. Two switches are utilized to realize the antenna with switchable beam shaping at constant frequency 5.8GHz. The antenna performance including return loss, bandwidth, half power beamwidth (HPBW), and radiation patterns are obtained using CST microwave simulation. II. ANTENNA DESIGN The configuration of the proposed reconfigurable antenna structures is shown in Figure 1. The structures of an antenna are constructed on FR-4 glass epoxy substrate with relative permittivity ( ε r ) is 4.6, loss tangent ( δ ) is 0.03 with height of substrate is 1.6 mm. The PIN diode switches are represented as dotted green rectangles at S1 and S2 in two locations as shown in Figure 1(a). The size of the switches is 2.5 x 1.4mm and the gap (g) between the transmission lines is designated as 0.5 mm. In this advance, a dc bias circuit is used to control the on/off mode of PIN diode switches, which will be changing the beam width by varying its number of elements. When all diodes are on mode, this antenna basically operates at a concave pattern (focusing/beam narrow). If opposite of this, all diodes are turn off, the patches will be reduce to four elements and produced a convex pattern (defocusing/beam broaden). A. PIN Diode RF Switching Circuit Philips PIN diodes, BAP51-02 were selected in this design. Figure 2(a) shows the schematic diagram of the switching circuit and inserted in between two transmission lines. Each switching circuit consists of a series connected 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 and provide low impedance for dc. The biasing 978-1-4244-2642-3/08/$25.00 ©2008 IEEE
voltage has been connected to 100 resistor to control the current flow to the switch. The simulation results using the PIN diode’s equivalent circuits, for the OFF and ON-state are presented at Figure 2(b). The return loss is better than 40dB when ON mode and approximate to 0dB for the OFF mode at 5.8GHz. B. Power Divider Concept The power divider concept is one of the most commonly component in transmission line for power division and/or combination ratio as an n-port network. There are two common types of power divider used in antenna design, that are Wilkinson power divider and T junction power divider. A Wilkinson power divider with an arbitrary power ratio is expressed as follows in, [6]. Another type power divider was used in this paper are T junction design [6], has 50 (Zo) line input impedances at each port, and a quarter-wave matching transformer with an impedance of 35.36 (Z1). III.
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 have been tuned efficiently, since its structure is symmetrical by the center, the pattern obtained is directed to 0. The radiation pattern of the 4 and 8 elements structure are shown in Figure 3, with HPBW of 220 and 12.60 respectively. It is showing clearly that when the number of elements is increased, the beamwidth became narrow with lower sidelobe and high magnitude. To tune the frequency from the previous results of return losses for a good match, a single open stub is necessary. Therefore, a single quarter-wavelength open stub with 100 impedance, which operates at 5.8GHz, is added to microstrip feeding line as shown in Figure 1b. After adding /4 stub matching, the measurement result of the resonant frequency is shifted to 5.8GHz when all PIN diodes are in ON state. Meanwhile the return loss for both structure are -29.43 dB and -23.56 dB respectively as shown in Figure 4. 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 4. The antenna shows good impedance matching for both cases with better than 20dB return loss is observed. In Figure 5, shows the measurement of return loss when the switches turn on and off-state. To tune the frequency from the previous results of return losses for a good matching, by 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 1(b). The measured radiation patterns, in Figure 6, show very good agreement with the simulation. The results shown that two different beam pattern at -3dB, is about 29o and 21o at the same frequency. Table 1, is the summarized of simulation and measurement result obtain for the reconfigurable linear array antenna. IV. CONCLUSION In this paper, experimental data was demonstrated the concepts of reconfigurable number of elements that produced broad beam and narrow beam radiating pattern characteristic. Using modified WPD in the antenna structure, produced better performance in term of return loss characteristic. This research has taken advantage of the flexibility of the number of element 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 was presented in this paper with excellent radiation patterns.
Acknowledgements: 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.
[1] [2]
[3]
[4]
[5] [6]
REFERENCES Madany, Y. M. ‘The analysis of wideband conformal microstrip array antenna with cosecant-squared beam shaping’,2006 IEEE Conference on, pp. 208-214. 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, Vol. 1, pp. 403-406, (2003). Rainee N. Simons, ‘Novel On-Wafer Radiation Pattern Measurement Technique for MEMS Actuator Based Reconfigurable Patch Antennas’ Glenn Research Center, Cleveland, Ohio 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). Peroulis, D., Sarabandi, K., Katehi, L. P. B., ‘Design of reconfigurable slot antennas’. IEEE Transactions on, Vol. 53, pp. 645-654, (2005). J.R. James, P.S. Hall, ‘Handbook of Microstrip Antennas’ Vol. 2, Peter Peregrinus Ltd., London United Kingdom, 1989 Figures
S1
S2 Single Stub matching
(a)
(b)
Figure 1: Reconfigurable linear array antenna (a) Schematic structure (b) Prototype of the fabricated antenna with single stub matching and PIN diodes. PORT P=2 Z=50 Ohm
S11 switch OFF MLIN ID=TL20 W=3 mm L=4 mm
MSUB Er=4.7 H=1.6 mm T=0.035 mm Rho=1 Tand=0.019 ErNom=4.7 Name=SUB1
0
MGAP2 ID=TL6 W=3 mm S=0.5 mm
CAP ID=C1 C=1.1 pF
-10
MLIN ID=TL18 W=3 mm L=1 mm MSUB=SUB1 MGAP2 ID=TL2 W=1.136 mm S=0.5 mm
1
MTEE$ ID=TL24
3
MLIN ID=TL14 W =1 mm L=5.5 mm
-20
2
IND ID=L2 L=22 nH
MLIN ID=TL12 W=3 mm L=1 mm MSUB=SUB1
dB
MLIN ID=TL16 W=1 mm L=10 mm
-30 MLIN ID=TL10 W=3 mm L=1 mm MSUB=SUB1
MGAP2 ID=TL1 W=1.136 mm S=0.5 mm
MGAP2 ID=TL3 W=1 mm S=1 mm
DCVS ID=V1 V=6 V
MLIN ID=TL7 W=1 mm L=10 mm
RES ID=R1 R=100 Ohm
-40
1
MTEE$ ID=TL25
3
MLIN ID=TL5 W=1 mm L=2 mm
S11 Switch ON
MGAP2 ID=TL4 W=3 mm S=0.7 mm
PINDD ID=P1
MLIN ID=TL11 W =1 mm L=5.3 mm
- 45.5dB MLIN ID=TL22 W=3 mm L=0 mm MSUB=SUB1
IND ID=L1 L=22 nH
CAP ID=C2 C=1.1 pF
S11 Switch ON state S21 Switch ON state S11 switch OFF state S21 Switch OFF state
2
-50
MGAP2 ID=TL8 W=3 mm S=0.5 mm
MLIN ID=TL13 W=3 mm L=23.71 mm MSUB=SUB1
PORT P=1 Z=50 Ohm
-60 3
4
5
6
7
8
Frequency (GHz)
(a) (b) Figure 2. (a) The switching circuit schematic components inserted in feeding line (b) Return loss (S11) results when switch ON / OFF state
0
Amplitude
-10
-20
-30
4 patches element - S1 and S2 OFF 8 patches element - S1 and S2 ON
-40 -100
-80
-60
-40
-20
0
20
40
60
80
100
Angle
0
0
-5
-5
-10
-10
Return Loss S11(dB)
Return Loss S11(dB)
Figure 3: Simulation results of normalized radiation pattern for 4 and 8 elements structure.
-15
20.57 dB
-20
-25
-30
-15
-20
- 20.57dB -25
29.66 dB
Measured 4 elements Simulation 4 elements
-23.56dB
-30 Simulation for 8 elements Measured for 8 elements
-35
-35
5.4
5.5
5.6
5.7
5.8
5.9
6.0
6.1
5.4
5.6
5.8
Frequency (GHz)
6.0
6.2
Frequency (GHz)
(a)
(b)
Figure 4: Simulation and measured return loss (a) 4 elements (b) 8 elements. 0
0
At 5.8 GHz
-20
Amplitude
Return Loss S11 (dB)
-10 -10
-20
8 patches antenna 4 patches antenna
-30
-40
-30
-50 Switch 1 and 2 OFF - 4 patches Switch 1 and 2 ON - 8 Patches
Measured switches off - 4 patches Measured switches on - 8 patches
-40
-60 4.4
4.6
4.8
5.0
5.2
5.4
5.6
5.8
6.0
-100
-50
Frequency (Ghz)
0
50
100
Degree
(a)
(b)
Figure 5: Measured results (a) S11 when switch on/off state (b) Normalized radiation pattern for 4 and 8 patches
TABLE 1: SUMMARY PERFORMANCE OF THE RECONFIGURABLE LINEAR ARRAY ANTENNA Ant
HPBW(0)
Return Loss S11(dB) Element Sim.
Meas.
Sim.
Meas
1
4
-29.66
-20.57
22
29
2
8
-23.56
-20.57
12.6
21
