S.X. Ta, I. Park and R.W. Ziolkowski
bandwidths were 1.217–1.240 GHz and 1.525–1.630 GHz, while the simulated 3dB AR bandwidths were 1.215–1.235 GHz and 1.53–1.60 GHz; good agreement between the two can also be observed. In addition, the measurement yielded the CP centre frequencies for the lower and upper bands of 1.228 and 1.579 GHz with an AR of 0.87 and 0.94 dB, respectively.
A dual-band, wide-beam, circularly-polarised crossed asymmetric dipole antenna is presented for global positioning system (GPS) applications. Each dipole arm has an asymmetrically barbed arrowhead and contains two different-sized printed-inductors to reduce the length of the primary radiating element and to achieve dual-band operation. At 1.575 GHz, the antenna has a gain of 7.5 dBic, a radiation efficiency of 97.4%, and a 3dB axial ratio (AR) beamwidth of 1438 and 1528 in the x-z and y-z planes, respectively. At 1.227 GHz, the antenna has a gain of 6.3 dBic, a radiation efficiency of 90%, and a 3dB AR beamwidth of 1328 and 1408 in the x-z and y-z planes, respectively.
top side s A
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Antenna design: Fig. 1 shows the geometry of the dual-band GPS antenna. The antenna comprises two printed dipoles, a coaxial feedline, and a cavity-backed reflector. The cavity is a rectangular box with dimensions of 120 × 120 mm2 and a height of Hc ¼ 40 mm. The printed dipoles were suspended in the centre of the cavity at a height of H ¼ 40 mm from the bottom of the reflector. The dipoles were printed on both sides of a Rogers RO4003 substrate with a relative permittivity of 3.38, loss tangent of 0.0027, and a thickness of 0.508 mm. Each dipole arm was divided into two branches, each of which contained a printed inductor whose end was shaped like a halfarrowhead [5]. To achieve dual-band operation, the printed inductors and the half-arrowhead-shaped ends of the conductors were designed with different sizes. The dipoles were crossed by a vacant-quarter printed-ring that acted as a 908 phase delay line [6]. The ANSYSAnsoft high-frequency structure simulator (HFSS) was used to design the antenna. The optimised parameters for the antenna were follows: A ¼ 52 mm, B ¼ 40 mm, Wc1 ¼ 26 mm, Wc2 ¼ 20 mm, Ri ¼ 6 mm, Wr ¼ 1 mm, Wb ¼ 5.4 mm, Lb1 ¼ 16 mm, Lb2 ¼ 13 mm, Li1 ¼ 10 mm, Li2 ¼ 7.8 mm, gi1 ¼ 0.6 mm, wi1 ¼ 0.6 mm, gi2 ¼ 0.4 mm, wi2 ¼ 0.6 mm, Ws1 ¼ 1.6 mm, Ws2 ¼ 2 mm, s ¼ 0.4 mm, Hc ¼ 40 mm, and H ¼ 40 mm. Simulation and measurement results: The dual-band GPS antenna was fabricated and measured. Fig. 2 shows the measured and simulated |S11| and AR values for the proposed antenna. The measured impedance bandwidths for |S11| , –10 dB were 1.188–1.265 GHz and 1.453–1.80 GHz, values which agree rather closely with the simulated bandwidth of 1.185–1.271 GHz and 1.444–1.749 GHz. The measured 3dB AR
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Fig. 1 Geometry of crossed asymmetrically barbed arrowhead dipoles
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Introduction: Circularly-polarised (CP) antennas have received much attention for various wireless communication systems, such as global positioning systems (GPS), satellite communications, radio frequency identification (RFID), and wireless local area networks (WLANs). In particular, CP radiation is generally adopted in GPS and satellite communications because the signals display less sensitivity between the satellite and ground station when they pass through the ionosphere. For real applications of GPS, the receiving antenna requires the covering of both the L1 and L2 bands, right-hand circular polarisation (RHCP), a 3dB axial ratio (AR) beamwidth greater than 1208 facing the sky, and a high front-to-back ratio in order to prevent interference from the ground. Various kinds of antennas with single-feed and CP radiation have been presented for dual-band GPS applications, including a multilayer substrate microstrip antenna [1], microstrip line-fed slotted antennas [2], and stacked patch antennas [3]. Most of the above-mentioned antennas, however, essentially concentrate on CP generation and 3dB AR bandwidth enhancement rather than improvement of the 3dB AR beamwidth. A pyramidal ground structure with a partially enclosed flat conducting wall has been adopted in order to increase the beamwidth of the CP radiation, but the configuration of the overall design is unwieldy and it operates only on a single L1 band with a gain less than 0 dBic [4]. This Letter presents a dual-band GPS crossed dipole antenna with a wide beamwidth, a high radiation efficiency, and a high front-to-back ratio. Two asymmetrically barbed arrowhead dipoles are employed not only to achieve dual-band operation, but also to reduce the size of the primary radiating element.
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Fig. 2 Simulated and measured |S11| and AR values ---- |S11| measured — |S11| simulated - - - AR measured -.-. AR simulated
Fig. 3 shows the radiation patterns at 1.575 and 1.227 GHz against the theta angle, the angle from the broadside z-direction. The measured radiation patterns agreed well with the HFSS simulated results. At 1.575 GHz, the radiation was RHCP with a gain of 7.5 dBic and a front-to-back ratio of 24 dB. At 1.227 GHz, the radiation was also RHCP with a gain of 6.3 dBic and a front-to-back ratio of 19 dB. Fig. 4 shows the AR values at 1.575 and 1.227 GHz against the theta angle. The measurement yielded very wide 3dB AR beamwidths that were 1438 and 1528 in the x-z and y-z planes, respectively, at 1.575 GHz, and 1328 and 1408 in the x-z and y-z planes, respectively, at 1.227 GHz. In addition, the measurement showed high radiation efficiencies of 97.4 and 90% at 1.575 and 1.227 GHz, respectively.
ELECTRONICS LETTERS 6th December 2012 Vol. 48
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Conclusion: A dual-band, CP, crossed asymmetrically barbed arrowhead dipole antenna is introduced for GPS applications with a broad bandwidth (1.188 – 1.265 GHz and 1.453– 1.80 GHz for |S11| , – 10 dB and 1.217– 1.240 GHz and 1.525 – 1.630 GHz for AR , 3 dB), a wide beamwidth (.1308 for the 3dB AR beamwidth), a high front-to-back ratio (.18 dB), and a high radiation efficiency (.90%). The crossed asymmetrically barbed arrowhead dipoles with differentsized printed-inductors were utilised not only to achieve dual-band operation, but also to reduce the length of the primary radiating elements. With its many advantages, this antenna can be widely applied for GPS purposes, as well as for satellite communications. # The Institution of Engineering and Technology 2012 13 August 2012 doi: 10.1049/el.2012.2890 One or more of the Figures in this Letter are available in colour online.
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S.X. Ta and I. Park (School of Electrical and Computer Engineering, Ajou University, Suwon, Republic of Korea) E-mail:
[email protected] R.W. Ziolkowski (Department of Electrical and Computer Engineering, University of Arizona, Tucson, Arizona, USA)
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References
Fig. 3 Radiation patterns of antenna
1 Chen, S., Liu, G., Chen, X., Lin, T., Liu, X., and Duan, Z.: ‘Compact dual-band GPS microstrip antenna using multilayer LTCC substrate’, IEEE Antenna Wirel. Propag. Lett., 2010, 9, pp. 421– 423 2 Hsieh, W., Chang, T., and Kiang, J.: ‘Dual-band circularly polarized cavity-backed annular slot antenna for GPS receiver’, IEEE Trans. Antenna Propag., 2012, 60, (4), pp. 2076–2080 3 Sun, X., Zhang, Z., and Feng, Z.: ‘Dual-band circularly polarized stacked annular-ring patch antenna for GPS application’, IEEE Antenna Wirel. Propag. Lett., 2011, 10, pp. 49–52 4 Su, C.W., Huang, S.K., and Lee, C.H.: ‘CP microstrip antenna with wide beamwidth for GPS band application’, Electron. Lett., 2007, 43, (20), pp. 1062–1063 5 Jin, P., Lin, C., and Ziolkowski, R.W.: ‘Multifunctional, electrically small, planar near-field resonant parasitic antennas’, IEEE Antenna Wirel. Propag. Lett., 2012, 11, pp. 200–204 6 Baik, J.W., Lee, K.J., Yoon, W.S., Lee, T.H., and Kim, Y.S.: ‘Circular polarised printed crossed dipole antennas with broadband axial ratio’, Electron. Lett., 2008, 44, (13), pp. 785– 786
—— RHCP measured - - RHCP simulated - - - LHCP measured -.-. LHCP simulated
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Fig. 4 AR values against u angle ---- x-z measured - - x-z simulated - - - y-z measured -.-. y-z simulated
ELECTRONICS LETTERS 6th December 2012 Vol. 48 No. 25
