[2-6], dipole antenna [7-11], and printed bow-tie antenna [12-15]. The quasi-Yagi provides up to. 48% bandwidth [2-6]. The microstrip-fed dipole provides 2:1 ...
A Microstrip-Fed Modified Printed Bow-Tie Antenna For Simultaneous Operation In The C and X-Bands Abdelnasser A. Eldek, Jackson State University Atef Z. Elsherbeni, The University of Mississippi Charles E. Smith, The University of Mississippi Key Words: Wideband Antennas, Bow-Tie Antennas, Phased Array Antennas
Abstract This paper presents a modified printed bow-tie antenna designed to simultaneously operate in the C and X-bands from 5.5 to 12.5 GHz. This new antenna design provides an end fire radiation pattern suitable for integration in single and dual polarized phased array systems. The antenna exhibits small size and wide bandwidth approaching 91%. The radiation characteristics are presented for a single element and for a linear array configuration. I. INTRODUCTION
impedance bandwidth in [7], [8], [9] and [10], respectively, and 1.5:1 VSWR of 30% in [11]. The microstrip fed modified dipole (bow-tie) antennas presented in [12-14] provide up to 50% bandwidth. Recently, the authors showed that replacing the dipole and the director of the quasi-Yagi antenna with a bow-tie for the X-band operations improves the bandwidth (60%), size, and radiation characteristics of the antenna [15]. Further research by the authors resulted in a novel coplanar waveguide fed slot and microstrip fed printed antennas, which are called slot and printed Lotus antennas [16]. The printed Lotus provides 57% bandwidth relative to –15 dB, and 60% relative to – 10 dB. The presented antennas, however, cannot simultaneously cover the C and X operating bands, which is the objective of this paper. This paper presents a modified printed bow-tie antenna that exhibits a wide bandwidth (BW). The return loss, VSWR and far field radiation characteristics of this antenna are presented. In addition, two array configurations are presented to improve the pattern stability across the operating bandwidth. The simulation and analysis for the presented antennas are performed using the commercial computer software package, Ansoft HFSS, which is based on the finite element method. Measurements of return loss, VSWR and radiation patterns are also conducted for verification of these new antenna designs.
Printed microstrip antennas are widely used in wireless communication and phased array applications. They exhibit a low profile, small size, light weight, low cost, high efficiency, and ease of fabrication and installation. Furthermore, they are readily adaptable to hybrid and monolithic microwave integrated circuits’ fabrication techniques at RF and microwave frequencies [1]. Communication and phased array systems that operate in the C and X-bands are normally designed using separate antennas for each band. Since it is becoming more and more important to use such systems in one setting, it is desirable to design a single antenna that operates in both frequency bands. This, in turn, requires a wideband antenna that covers the two bands. In addition, many applications require end fire patterns, which can be produced by different types of antenna elements. Among the most widely used printed antennas II. ANTENNA GEOMETRY AND RESULTS in phased array systems are the quasi-Yagi antenna The proposed antenna is printed on a Rogers [2-6], dipole antenna [7-11], and printed bow-tie RT/Duroid 6010/6010 LM substrate of a dielectric antenna [12-15]. The quasi-Yagi provides up to 48% bandwidth [2-6]. The microstrip-fed dipole constant of 10.2, a conductor loss (tan δ) of 0.0023 provides 2:1 VSWR of 19%, 50%, 56%, and 40% and a thickness of 50 mil (1.27 mm). The geometry
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and parameters of the proposed antenna are shown in Fig. 1. The antenna consists of two identical printed bows, one on the top and one on the bottom of the substrate material. The top and bottom bows are connected to the microstrip feedline and the ground plane through a stub and mitered transition to match the bow-tie with the 50 Ω feedline, as illustrated in Fig. 1. The antenna dimensional parameters, shown in Fig. 1, Wf, W1, W2, W3, W4, W5, Lf, L1, L3, L3. L4, L5, L6 and L7 are 1.2, 1.52, 0.45, 0.62, 2, 2.49, 10, 5.34, 0.45, 0.68, 0.24, 2.61, 5.56, and 9.68 mm, respectively. The substrate size (width×length) is (30×29) mm2. This antenna is fabricated and the top and bottom views for its prototype are shown in Fig. 2. The return loss and VSWR are computed using Ansoft HFSS and measured using a 8510 vector network analyzer and are shown in Figs. 3 and 4. The small discrepancies between the computed and measured results may occur because of the effect of the SMA connector and fabrication imperfections. Both the simulation and measurements show that the antenna operates over a wide range that extends from 5.3 GHz to more than 14.2 GHz, with an impedance bandwidth of approximately 91%. The measured and computed radiation patterns at the operating band center frequency, 9 GHz, are shown in Fig. 5. A good agreement is noticed, which further verifies the simulation results using Ansoft HFSS. The radiation patterns are then computed at selective frequencies that cover almost the entire operating band, and shown in Fig. 6 at 6, 8, 10, and 12 GHz. The properties of these patterns are summarized in Table 1. Good radiation characteristics are obtained up to 10 GHz. The radiation pattern starts to deteriorate at 12 GHz. For the frequencies less than 12 GHz, the antenna has wide beamwidth that ranges from 95 to 150o in the E-plane and from 115 to 180o in the H-plane. It has a maximum cross polarization level of –20 and –18 dB in the E and H planes, respectively, and a minimum front to back ratio (F-to-B) of 12 dB. The antenna gain has an average value of 6 dB.
Top Layer Substrate Bottom Layer and ground plane W4 W5
L7 L6
L2,L3,L4,L5
W3 L1
W2 W1
y Lf
x Wf Top layer
z
y Substrate
x
εr = 10.2 h = 50 mil
Bottom layer
Ground
plane
Fig. 1. Antenna geometry and parameters.
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Prototype top view
Prototype bottom view
Measured Eφ
Measured Eθ
Computed Eφ
Computed Eθ
Fig. 2. Antenna prototype.
(a)
Fig. 3. The measured and computed return loss for the modified bow-tie antenna.
(b) Fig. 5. Comparison between the measured and computed radiation patterns in the (a) Eplane and (b) H-plane, for the modified bow-tie antenna at 9 GHz. Fig. 4. The measured and computed VSWR for the modified bow-tie antenna.
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Measured Eφ
Measured Eθ
Computed Eφ
Computed Eθ
(a)
(b)
(c)
(d)
Fig. 6. Computed radiation patterns at (a) 6, (b) 8, (c) 10, and (d) 12 GHz.
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Table.1. Far field radiation properties. f (GHz) 6 8 10 12
3dB beam width EHplane plane 105o 150o o 95 115o o 150 125o o 50 N/A
Xpol. level (dB) EHplane plane -23 -18 -25 -25 -20 -18 -13 -4
5.
F-to-B (dB)
Gain (dB)
16 13 12 1
5 7 5 5
A wideband microstrip-fed modified printed bow-tie antenna is designed for C and X-band operations. The modified bow-tie antenna provides 91% impedance bandwidth that covers the entire C and X bands and part of the Ku band. The single element antenna provides wide beamwidth (more than 95o), low cross polarization level (less than –18 dB), and relatively high gain in the frequency range between 5.3 and 10 GHz. Furthermore, it produces an endfire radiation patterns with a good front-toback ratio that exceeds 12 dB. According to these results, the operating bandwidth of the antenna, as a single element, is between 5.3 and 10 GHz, which is around 61.4%. However, when used in phased array applications, unconventional arrangement of the elements of this antenna can further improve the radiation characteristics at higher frequencies approaching 12 GHz.
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REFERENCES
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7. 8.
III. CONCLUSION
1.
6.
L. G. Maloratsky, “Reviewing the basics of microstrip lines,” Microwave & RF. pp. 79-88, March 2000. Y. Qian, W. R. Deal, N. Kaneda, and T. Itoh, “Microstrip-fed quasi-Yagi antenna with broadband characteristics,” Electron Lett., vol. 34, no. 23, pp. 2194-2196, 1998 N. Kaneda, Y. Qian, and T. Itoh, “A broad-band microstrip-to-waveguide transition using quasi-Yagi antenna,” IEEE Trans. Microwave Theory and Tech. vol. 47, no. 12, pp. 2562-2567, Dec. 1999. W. Deal, N. Kaneda, J. Sor, Y. Qian, and T. Itoh, “A new quasi-Yagi antenna for planar active antenna arrays,” IEEE Trans. Microwave Theory and Tech. vol. 48, no. 6, pp. 910-918, June 2000.
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