Reconfigurable Beam Steer Antenna (RBSA) Design

2012 Loughborough Antennas & Propagation Conference

12 - 13 November 2012, Loughborough, UK

Reconfigurable Beam Steer Antenna (RBSA) Design for WiMAX Application M. Jusoh1, M. F. Jamlos2, Hasliza A. Rahim3

M. F. Abd Malek

School of Computer and Communication Engineering Universiti Malaysia Perlis (UniMAP), Kampus Pauh Putra 02600 Arau, Perlis, MALAYSIA 1 [email protected] 2 [email protected] 3 [email protected]

School of Electrical System Engineering, Universiti Malaysia Perlis (UniMAP), Kampus Pauh Putra 02600 Arau, Perlis, MALAYSIA [email protected]

M. R. Kamarudin

M. R. Hamid Radio and Communication Engineering Department, Faculty of Electrical Engineering, Universiti Teknologi Malaysia Skudai, Johor, Malaysia [email protected]

Wireless Communication Centre, Faculty of Electrical Engineering, Universiti Teknologi Malaysia Skudai, Johor, Malaysia [email protected] Abstract— A reconfigurable antenna design for beam steer capability (RBSA) is proposed in this research. The RBSA has successfully achieved beam steer functionality at three angle direction of -42°, -28° and -15°. This is achieved by certain PIN diode configuration. The PIN diode is positioned at the specific location of the RBSA feed network. The proposed antenna consists of an array of three rectangular radiating elements. Aperture coupled feed technique applied in order to reduce the deterioration of power due to the presence of the PIN diode. RBSA has a small dimension of 100 mm x 100 mm that design on Taconic substrate. All designs and simulations have been carried out using CST Microwave Studio. This antenna is potentially useful for Wireless Interoperability Microwave (WiMAX) smart antenna system. Keywords-beam antenna;

steer;

I.

reconfigurable

beam;

WiMAX

INTRODUCTION

Moving towards smart and compact size antenna, a reconfigurable antenna is a great selection to be considered. Reconfigurable antenna is capable to perform multifunction in a single antenna design. The antenna can be applied to reconfigure frequency (single band to multi-band), reconfigure polarization (vertical to horizontal, LHCP and RHCP) and reconfigure the radiation pattern (shaped, steered, broadside, end fire, omnidirectional) as well. One way to realize a reconfigurable antenna by means of RF switches such as PIN diodes, MEMs and GaAs FETs. The most popular RF switch is PIN diode due to the ease of fabrication and fast response time [1]. The PIN diode can be used to obtain frequency tuning [2–4] and as impedance matching devices as well [5-6]. This research proposed a reconfigurable beam steer antenna (RBSA) suitable for point-to-point communication system. The RBSA is successfully designed to steer at three dedicated angle of -42°, -28° and -15°. Thus, an array antenna technique has been applied as discussed in [7-8]. The 978-1-4673-2220-1/12/$31.00 ©2012 IEEE

antenna is compact with dimension of 100 mm x 100 mm as compared to [8-9]. The aperture coupled feed technique with spiral arm feed is introduced. The feed network is functioning as a power divider of an array antenna. A quarter wavelength transformer is used to match the transmission line in order to fix 50Ω of input port impedance. Electromagnetic wave is coupled to the radiating element via aperture slots. Therefore, the positioned and dimension of the slot is really significant. This will reflect to more power is transferred to the antenna element rather than reflected back to the source (SMA connector). It is discovered, a spiral feed helps to achieve a beam steer ability. The presented RBSA that working at a resonant frequency of 2.39 GHz is a suitable candidate for Wireless Interoperability Microwave (WiMAX) applied as regulated by the Malaysian Communication and Multimedia Commission (MCMC). MCMC is a trusted body that controlled all the spectrum allocation in Malaysia. MCMC has allocated frequency of 2.3 GHz to 2.39 GHz for WiMAX application in Peninsular Malaysia, Sabah and Sarawak [10]. II.

ANTENNA DESIGN

Fig.1 shows the configuration of the proposed RBSA. The antenna used an aperture coupled feed technique. This technique separates the microstrip feed and the radiating element on the different antenna’s substrate. Three rectangular shape radiator has been designed on the top layer of substrate. The bottom layer of substrate consists of feed network. All power excited from the input impedance will be transferred to the top substrate via a rectangular slot that functioned as an EM couple. A specific slot location of 10 mm from the edge radiating has resulted to the more power transferred to the radiating rather than reflected to the source.


100 mm

100 mm

100 mm

12 - 13 November 2012, Loughborough, UK transfer of frequency dependent n-port parameters [16]. The implementation of TSB diode in CST Microwave Studio software is shown in Fig. 2(a) ON state and 2(b) OFF state.

100 mm

1

1

2

1'

2'

1

2

diode ON state.s2p

(a)

(b)

100 mm (b)

100 mm

(a)

1

100 mm

i i

ii

100 mm

PIN diode

1

2

1'

2'

1

2

diode OFF state.s2p

i ii iii (b)

Figure 2 Schematic diagram of the TSB implementation to the antenna design. (a) ON state. (b) OFF state. (d)

Figure 1 Geometry of the simulated antenna structure (a) Radiating element surface (b) Rectangular slot aperture coupled. (c) Spiral feed. (d) Spiral feed line arrangement. The RBSA has been printed on the Taconic (TLY-5) substrate with dielectric of εr = 2.2, thickness of t = 1.5478+/-0.02, tangent loss of tanδ = 0.0009 and copper thickness of 35μm. It has a novel design of the spiral arm feed network. This is to ensure the antenna size reduction instead of using a straight line feed. Moreover, the proposed antenna has a dimension of 100 mm x 100 mm with the ability of beam steering. The reconfigurable beam steer antenna is achieved via the integration of the PIN diode to the RBSA feed network instead of radiating element. This helps to minimize power deteriorates by the introduction of the surface mount component (SMC) [11-15]. SMC consists of one PIN diode, two DC (direct current) block capacitor, two RF choke inductor and a DC supply. The PIN diode reacts to ON state when there is a DC current flow to it. The inductors play a major role to ON the PIN diode instead chokes the alternating current (AC) from flow to the DC supply and ground. Whereas capacitors will block the DC current and allow RF signals to flow simultaneously. All designs and simulations have been carried out by CST Simulation Software. Three PIN diode switches has been used that represent as A, B and C. In the simulation, RF switch can be presented by copper strip line or touch stone block (TSB). Papers in [11-15] discussed that ON state and OFF state mean input current can flow from one point to another point and vice versa. Therefore the presence and absence of copper strip indicate ON state and OFF state conditions respectively. While TSB that known as SnP file is an ASCII text file used for documenting the n-port network parameter data of an active device or passive interconnect network. It has been accepted as a de facto standard for the

III.

RESULT AND DISCUSSION

Figure 3 illustrates a reflection coefficient result of PIN diode in ON state between copper strip and TSB method. The result shows that no significant difference. Both results have frequency resonant at 2.38 GHz. However, the impedance matching for the TSB is better compared to the copper strip line. Q factor or Quality factor is really significant in antenna design. Q factor is losses that obstruct the antenna performance. It has an inverse relation to the antenna efficiency. Total Q can be determined from the Equation 1 with a consideration of the voltage standing wave ratio (VSWR) and fractional bandwidth (FBW). The FBW is a deduction of high order mode (fH) to the low order mode (fL) over a center frequency (fo) [17]. Table 1 shows the RBSA has various Q and radiation efficiency according to the certain PIN diode configurations. 0

Return Loss, dB

(c)

-10

-20

-30

Copper Strip Line TSB -40 2.0

2.2

2.4

2.6

2.8

3.0

Frequency, GHz

Figure 3 Reflection coefficient comparison of copper strip line against touch stone block (TSB)


12 - 13 November 2012, Loughborough, UK

(1)

(2) (3)

Table 1 Simulated Q factor of the RBSA antenna. Switch of State Q factor BWfractional Radiation Efficiency (%) Total Efficiency (%)

Reconfigurable PIN diode BC ABC CA 82.3 97.68 74.4 8.5915 x 7.239 x 9.50 x 10-3 10-3 10-3 85.00

85.45

86.14

83.68

83.74

85.97

(a)

The proposed RBSA has successfully achieved beam steer ability with certain PIN diode switches configuration as depicted in Figure 4 and Table 2. As switches B and C are ON, the RBSA competent to steer at -15° with peak gain of 6.281dBi. As all switches are ON, the RBSA capable to steer at -28° with maximum peak direction of 5.542dBi. As switches A and C are ON, the RBSA accomplished to steer at -42° with a gain of 5.154dBi. Besides, all three PIN diode configurations achieved to function at 2.4GHz.

(b)

Table 2 PIN diode switches configuration of simulated RBSA Number of Type of Switch PIN diode PIN diode status switch A

OFF

ON

ON

B

ON

ON

OFF

C

ON

ON

ON

Simulated Resonant Frequency (GHz)

2.39

2.39

2.39

Simulated Angle of Beam Steer

-15°

-28°

-42°

Simulated Gain (dBi)

6.281

5.542

5.154

Reconfigurable PIN diode

(c) Figure 4 Simulated radiation pattern of the RBSA antenna. (a) PIN diode B and C are ON. (b) PIN diode A, B and C are ON. (c) PIN diode A and C are ON. The PIN diode that not mentioned is in OFF state. IV.

CONCLUSION

A reconfigurable beam steer antenna (RBSA) operates at 2.39 GHz is presented. The antenna can steer the beam at 42°, -28° and -15°. Besides, a novel design of RBSA has a gain up to 5 dBi. With the implementation of aperture coupled feed technique, it has a small physical dimension of 100 mm x 100 mm. The proposed RBSA is potential for WiMAX smart antenna system.

2012 Loughborough Antennas & Propagation Conference REFERENCES [1]

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12 - 13 November 2012, Loughborough, UK [12] M.Jusoh, M.F.Jamlos, M.F.Malek, M.R.Kamarudin and M.S.Mustafa, “A Switchable Ultra-wideband (UWB) to Tri-Band Antenna Design,” 2011 Loughborough Antennas & Propagation Conference, 14-15 November 2011, Loughborough, UK. [13] M.Jusoh, M.F.Jamlos, M.R.Kamarudin and M.F.Malek, “A Novel Compact Reconfigurable Multi-Band Antenna,” 2011 IEEE Radio Frequency and Microwave (RFM), 12-14 December 2011, Seremban, Malaysia. [14] M. F. Jamlos, O. A. Aziz, T. A. Rahman, M. R. Kamarudin, P. Saad, M. T. Ali and M. N. Md Tan, “A Reconfigurable Radial Line Slot Array (RLSA) Antenna for Beam Shape and Broadside Application,” J. of Electromagnetics Waves and Appl., Vol. 24, 1171–1182, 2010. [15] M.Jusoh, M.F.Jamlos, M.F.Malek, M. R. Kamarudin and M.R.Hamid “A Reconfigurable Beam Shape Patch Array Antenna (RBS-PA) for WiMAX and WiFi Applications”, IEEE International Asia Pacific Symposium on Electromagnetic Compatibility (APEMC), 21-24 May 2012, Sentosa Island, Singapore – To be published. [16] www.agilent.com [17] Constantine Balanis. Antenna Theory; Analysis and Design. 3rd Edition, 2003. John Wiley & Sons.