Design of Reconfigurable Radiation Pattern RingDipole Antenna for Wireless Communication Imen BEN TRAD1,2, Jean Marie FLOC'H2, Hatem RMILI3, M'hamed DRISSI2 and Fethi CHOUBANI1 1
INNOV'COM, Sup'Com, City of Communication Technologies, 2083 Ariana, Tunisia, (
[email protected]). 2 IETR, INSA, 20 Avenue Buttes des Coësmes, 35043 Rennes, France. (
[email protected]). 3 King Abdulaziz University, Faculty of Engineering, Electrical and Computer Engineering Department, P.O. Box 80204, Jeddah 21589, Saudi Arabia (
[email protected]).
Abstract—A printed planar micro-strip fed dipole antenna with reconfigurable radiation pattern properties is suggested for wireless communication. The structure consists of two resonant rings, each one is printed on one substrate layer. The dipole can switch its radiation pattern in different directions depending on the state of six PIN diode switches loaded on the resonant rings (three PIN diodes on every resonant ring). The designed antenna works at 2.4 GHz when all switches are ON and adopts a multifrequency behavior for different states of switches. Initial results were obtained by using short and open circuits instead of implanting PIN diodes. Results at 1.54 GHz are presented and discussed. A prototype was manufactured and characterized, then measured results were compared to simulations. Index Terms—Reconfigurable antenna; Radiation pattern; PIN Diode; Dipole
I.
II.
ANTENNA DESIGN
The basic structure of the planar reconfigurable radiation patterns antenna is a micro-strip fed dipole for which design parameters were optimized to operate at 2.4GHz. This antenna was obtained by printing two resonant rings on Rogers Duroid™ 5880 substrate (L=70mm, W=65mm) of thickness 0.8mm and relative permittivity r = 2.2. The first resonant ring (D=24mm, e=1mm) and the micro-strip feeding line (Lf=36mm, Wf=2mm) were printed on the top layer. The second one and the ground plane (Lg=10mm, Wg =20mm) were printed on the bottom layer. Then, six PIN diode switches were placed on the two resonant rings to alter the current direction, achieving hence the beam tilting.
INTRODUCTION
Recently, reconfigurable antennas are becoming more and more desired in many wireless communication systems, thanks to their ability to tilt their frequency of operation, polarization and radiation pattern dynamically without requiring much complexity [1-3] expanding eventually the capability of these systems. In particular, radiation pattern agility characteristic at a fixed operation frequency has received much attention because it can be used to avoid noise source, improve security and save energy by better directing signal toward intended users [4]. Several switching technologies are used to obtain agility such as MEMS (Micro-Electro-Mechanical-Systems) switches, varactor diodes and PIN diodes [5 - 6]. Several designs of reconfigurable radiation pattern antennas, especially planar reconfigurable radiation pattern antennas, have been widely investigated because of their attractive features such as simple structure, low profile, light weight and ease of fabrication and integration. In this paper, a planar printed micro-strip fed antenna with reconfigurable radiation patterns performance is designed. Depending on the states of switches, four resonance frequencies (1.21, 1.4, 1.54 and 1.8 GHz) have been observed. At every frequency from these ones, the radiation pattern reconfiguration is achieved. This structure is a very suitable candidate for wireless communication.
PIN Diode Switch
Resonant Rings
Ground plane
(a)
S4 S5
S1 S2
D
e S6
Lf
L S3
Wf
Lg W (b)
Wg (c)
Fig.1 (a) Schema of the reconfigurable dipole antenna: (b) top view; (c) back view
Fig.1 illustrates the geometry of the designed reconfigurable radiation patterns antenna and Fig.2 depicts the photos of the prototyped dipole before the integration of switches.
(a)
Here, we restrict ourselves to the 1.54GHz resonance frequency obtained at three cases. The first case is when switches S3 and S5 are OFF (S1, S2, S4 and S6 are ON), the second one is when S1 and S5 are switched OFF (S2, S3, S4 and S6 are ON) and the third case is when switches S3 and S6 are OFF (S1, S2, S4 and S5 are ON). The related simulated return loss is depicted in Fig.2.
(b)
Fig. 2 Photos of the realized prototype (a) Top view; (b) Back view
III.
RESULTS
The antenna was designed using the HFSS 13 commercial software and was optimized to work at the frequency 2.4 GHz when all switches are ON. The diameter D of the resonant ring, at this resonant frequency, corresponds to the quarterwave length (π×D/2 ≈ eff/4,eff is the effective wavelength in the heterogeneous medium). The measured return loss agrees well with the simulated one.
Fig.4 Simulated return loss at the resonance frequency 1.54GHz for 3 switching cases.
The measured return loss at these same cases exhibits a slight shift of 160 MHz compared to the simulated results as it can be seen in Fig.5. This may be assigned to the manufacturing errors.
0 -2
Return loss, dB
-4 -6 -8
-10 -12
Measurued S11 Simulated S11
-14 -16 0,5
1
1,5
2
2,5
3
3,5
4
Frequency, GHz Fig.3 Simulated and measured return loss at the resonance frequency 2.45 GHz (when all switches are ON).
The radiation mechanism is dynamically piloted by tuning the switches which transform the current distribution. Thereby, four new lower resonance frequencies appeared at 1.21, 1.4, 1.54 and 1.8 GHz. At each resonance frequency and depending on the switche's states, the radiation pattern should be able to tilt in different directions.
Fig.5 Measured return loss at the resonance frequency 1.54GHz for 3 switching cases.
The assessment of the different simulated 3D radiation patterns of the printed planar antenna presented in Fig.6 shows that in case1 the radiation pattern has the shape of dual-beam
oriented in the central axis (ox) of the structure. In the second case, the structure acts as a magnetic dipole; the radiation pattern of the antenna in the H-plane is omni-directional. Finally, the antenna works as an electric dipole in case3; an omni- directional radiation pattern in the E-plane is obtained.
four beams appeared. A dual-beam are oriented towards the antenna axis (oz) and the two remaining ones are oriented towards the (oy) axis. Hence, the radiation pattern can be easily tweaked depending on the switch conditions. The discrepancy in the measured radiation patterns can be attributed to the coaxial cable feed, the fabrication errors and the unforeseen alteration of surface current distribution due to the integration of short and open circuits.
(a)
(a)
(b)
(b)
(c) Fig.6 3D simulated radiation patterns (a) S3 and S5 OFF; (b) S1 and S5 OFF and (c) S3 and S6 OFF.
The measured 3D radiation patterns in the three cases previously described are presented in Fig.7. As it can be concluded, measurements confirm that by turning switches ON or OFF, the radiation pattern of the proposed dipole antenna gets the reconfigurable pattern characteristic. However, simulated results are different from measured ones; in the first case (when S3 and S5 are OFF), the antenna behaves as an electric dipole. An omni- directional radiation pattern in the (yoz) plane is well reached. In the second case, the radiation pattern maintains the same omni-directional behavior with a lag of 45º upwards, in the (xoz) plane, from its position in the first case. By turning OFF the switches S3 and S6 (third case),
(c) Fig.7 3D measured radiation patterns (a) S3 and S5 OFF; (b) S1 and S5 OFF and (c) S3 and S6 OFF.
IV.
CONCLUSION
A planar reconfigurable radiation patterns micro-strip fed dipole antenna was successfully designed to operate at 2.4 GHz
when all switches are ON. By tuning alternately the PIN diode switches, four lower resonant frequencies with reconfigurable radiation pattern properties at each frequency are obtained. First simulation results have been provided using short and open circuits instead of PIN diodes. Only the results at 1.54GHz resonance frequency are shown here. A prototype was manufactured and the measurements were carried out and compared to the simulations.
[3]
[4]
[5]
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