Proceedings of the Asia-Pacific Microwave Conference 2011
RF MEMS-Integrated Frequency Reconfigurable Quasi-Yagi Folded Dipole Antenna Eugene Siew #1, King Yuk (Eric) Chan#*2, Yong Cai *3, Yi Yang #4, Rodica Ramer #5, Andrew Dzurak #6 #
School of Electrical Engineering & Telecommunications, The University of New South Wales (UNSW), Sydney Australia. 1
[email protected] * The Commonwealth Scientific and Industrial Research Organization (CSIRO) Information and Communications Technology (ICT) Centre Cnr Vimiera & Pembroke Roads, Marsfield, NSW, 2212, Australia Abstract — A RF MEMS integrated frequency reconfigurable quasi-Yagi folded dipole antenna is presented. The operating frequencies of the antenna are interchangeable between the millimeter wave WPAN band (57-66 GHz) and E-band (71-86 GHz). This is achieved by electronically tuning the effective electrical length of the folded dipole driver and the director element by employing RF MEMS switches. Simulation results show that the integration of RF MEMS switches had little effect onto the antenna performance. End-fire radiation patterns with low cross polarization levels were achieved across the entire tunable frequency range. Simulation results show that the antenna gain lies between 4.3 dBi to 5.2 dBi in the lower band and between 5.5 dBi to 8 dBi in the upper band.
by varying the effective electrical length of the folded dipole driver and the director element, which is controlled by the actuation of the RF MEMS switches. RF MEMS switches are used because they exhibit high isolation, low dc power consumption, excellent linearity [7] and are more suitable compared to semiconductor devices when it comes to millimeter wave applications [8]. To this end, RF MEMS switches have been widely employed in the designs of reconfigurable filters for multi-standard radio front end [9], phase shifters [10], switch matrix [11], and reconfigurable antennas [12]-[13]. The paper is divided into four sections. Section I is the introduction. Section II describes our proposed antenna design. Simulation results are presented in Section III and Section IV concludes with a summary and suggestions for further work.
Index Terms — RF MEMS, folded dipole, reconfigurable antennas, quasi-Yagi antenna.
I. INTRODUCTION In the today’s communications systems, it is very much desirable for antennas to operate between the unlicensed WPAN spectrum (57-66 GHz) and the light licensed E-band spectrum (71-86 GHz) that has become increasingly popular around the world. Potential applications include high-speed, point-to-point wireless local area networks, broadband internet access, and radar systems with very high resolution. Another reason for its increasing popularity is due to its shorter wavelengths, these bands permit the use of smaller size antennas to achieve the same high directivity and high gain when compare to antennas that operate in the lower bands. To be able to fully utilize both the WPAN and E-Band spectrum in a single wireless platform, the antennas need to cover multiple frequency bands. While multiband and wideband antennas are potential candidates to achieve this, frequency reconfigurable antennas [1]-[2] are usually employed due to their better noise rejection capability which greatly reduces the filter requirements of the front-end circuits. Printed quasi-Yagi antennas have received considerable attention due to their low cost, high radiation efficiency, modest gain [3]-[4], ease of fabrication and integration with monolithic microwave integrated circuits (MMICs). In this paper, a RF MEMS integrated frequency reconfigurable quasi-Yagi folded dipole antenna is proposed for the first time as an extension to the work presented in [5][6]. The center frequency of the antenna can be reconfigured
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II. ANTENNA DESIGN The layout of the proposed reconfigurable antenna is shown in Fig. 1 followed by its dimensions in Table I. The antenna element is printed on a low-loss Quartz substrate ( r = 3.75, thickness h = 0.254 mm, tan = 0.0004), on which the RF MEMS switches are integrated. The top side of the substrate consists of a microstrip feeding line, a broad-band microstrip-to-CPS balun, a folded dipole driven element and a parasitic dipole element as a director. The bottom side is a truncated ground plane, which serves as a reflector element for the antenna. The combination of the parasitic director, the driven element and the reflector direct the radiation of the antenna toward the end-fire direction. It has been reported in [3, 14] that the length of the folded dipole driver L7, the length of the director L8, and the ratio of the upper strip and lower strip width W6/W8 are important design parameters of the quasi-Yagi folded dipole antennas. A total of eight RF MEMS switches (6 horizontal and 2 vertical) are used in this antenna. When all vertical switches are closed and all horizontal switches are opened, the length of the folded dipole is about 2*(L7+W7) and the length of the director is L8. Both the folded dipole and director are shorter in length, thus the antenna resonates at a higher operating
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RF MEMS
Fig. 2. switch .
Schematic layout of the cantilever beam based RF MEMS
E-Band WPAN Band Fig. 1. Schematic layout of the RF MEMS integrated frequency reconfigurable quasi-Yagi folded dipole antenna
TABLE I DIMENSION OF ANTENNA Parameters W1 W2 W3 W4 W5 W6 W7 W8 W9 W10 W11
Value (ȝm) 180 260 80 60 80 147 70 60 100 70 105
Parameters L1 L2 L3 L4 L5 L6 L7 L8 L9 L10 L11
Fig. 3. Comparison of the antenna reflection coefficient in upper band (blue curves) and lower band (red curves). Solid line: quasiYagi folded dipole antenna with RF MEMS switches integrated. Dashed line: quasi-Yagi folded dipole antenna without RF MEMS switches.
Value (ȝm) 540 600 240 260 600 105 1030 770 270 1065 1200
switched between WPAN band to the E-band. To understand our proposed RF MEMS reconfigurable antenna and the effect of RF MEMS switches, two non-reconfigurable antennas one operates at WPAN band and the other operates at E-bands are designed. They are used as benchmarks for the proposed reconfigurable antenna. Fig. 3 presents the reflection coefficient of the reconfigurable antenna in State I and State II and the two benchmark antennas. The simulation shows that the reconfigurable antenna achieves similar bandwidth in each band compared with the corresponding benchmark antennas. In both states, good impedance matching were achieved (|S11|
