1264 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 57, NO. 4, APRIL 2009
Microstrip-Fed Circularly Polarized Square-Ring Patch Antenna for GPS Applications
Hua-Ming Chen, Yang-Kai Wang, Yi-Fang Lin, Che-Yen Lin, and Shan-Cheng Pan
Abstract—A novel coupling technique for circularly polarized square-ring patch antenna is developed and discussed. The circular polarization (CP) radiation of the square-ring patch antenna is achieved by a simple microstrip feed line through the coupling of a square patch on the same plane of the antenna. Proper positioning of the coupling square patch ex-cites two orthogonal resonant modes with 90 phase difference, and a pure circular polarization is obtained. The dielectric material is a square block of ceramic with a permittivity of 58 and that reduces the size of the an-tenna. The prototype has been designed, fabricated and found to have an impedance bandwidth of 1.1% and a 3-dB axial-ratio bandwidth of about 0.03% at GPS frequency of 1573 MHz. The characteristics of the proposed antenna have been studied by simulation software HFSS and experiments. The measured and simulated results are in good agreement.
Index Terms—Ceramic dielectric material, circular polarization (CP), global position system (GPS), square-ring patch antenna.
I. INTRODUCTION
Circularly polarized patch antennas are widely used in some mo-bile satellite communications and most communication systems. Cir-cular polarization (CP) has advantage of greater flexibility in orien-tation angle between transmitter and receiver and reduction in multi-path reflections. A typical technique for producing circular polarization wave involves the use of feeding structure to excite two orthogonal lin-early polarized modes of equal amplitude and a 90phase difference [1]–[11]. The well-known method for obtaining circular polarization using single-feed patch antenna involves slotting and truncating the corner of the square patch antenna [1]–[9]. Since the two near-degen-erate orthogonal modes of equal amplitude and the 90phase differ-ence were excited, the purity of polarization will be relatively less.
For the square-ring patch antenna, its patch size is smaller than the conventional square patch antenna when operated at the fundamental mode (TM11 mode). However, when the square-ring patch antenna with a larger inner slot size or higher substrate thickness is excited at itsTM11mode, which has a lower resonant frequency and wider bandwidth, it would be difficult to obtain the 50- input impedance on the patch area.
In [6] and [7], the CP design is achieved by inserting a pair of slits or by adding two orthogonal strips at the inner boundary of the an-nular-ring patch. In [6] and [10], CP of the anan-nular-ring patch antenna is achieved by using the impedance transformer of microstrip feeding line or by using different coupling slots to overcome the high input impedance problem.
In this paper, we present a new coupling design of circular polar-ization for square-ring patch antenna with a simple microstrip feeding structure for GPS applications. The CP design of the square-ring patch
Manuscript received March 01, 2008; revised November 27, 2008. Current version published April 08, 2009. This work was supported in part by the Na-tional Science Council of Taiwan under Contract NSC96-2221-E-151-003.
H. M. Chen, Y. K. Wang, Y. F. Lin, and C. Y. Lin are with the Institute of Photonics and Communications, National Kaohsiung University of Applied Sciences, Kaohsiung 807, Taiwan (e-mail: [email protected]; linyf@cc. kuas.edu.tw).
S. C. Pan is with the Department of Computer and Communication, Sue-Te University, Kaohsiung 824, Taiwan.
Digital Object Identifier 10.1109/TAP.2009.2015855
antenna operates in theTM11mode obtained by a small square patch coupling to the square-ring patch at the same plane. Several square-ring patch antennas with different relative permittivity and thickness of sub-strate are constructed and simulated for verifying the proposed CP cou-pling method. Details of the antenna design and the experimental re-sults of the performance of antenna are presented and discussed.
II. ANTENNACONFIGURATION
The structure of the microstrip-fed square-ring antenna with a ce-ramic dielectric substrate is shown in Fig. 1. It is mounted on an FR4 feed substrate of thicknessh = 1:6 mm and a relative permittivity of 4.4. The ground plane is printed on the FR4 feed substrate with an area ofLg2 Wg(30 mm2 30 mm). In this design, an FR4 feed substrate is chosen, so the 50- microstrip feed line with Wf = 3 mm and Lf = 9 mm is fixed and located at the center of the ground plane. A
circular patch of radiusR = 3 mm is connected to the end of the mi-crostrip transmission line for the tuning stub. The square ceramic block has side length ofL = 15 mm, height of H = 3 mm and a relative permittivity of"dr = 58 (with tan = 0:001), which lies on the top side of the center of the feed substrate. The width of the square-ring radiation patch isW and has a gap of d from the edge of the ceramic block, which is fabricated by printing the conductive silver ink on the top side of the ceramic block. In addition, a coupling square patch with two side lengths ofLsandWslies in the second quadrant and at the same plane of square-ring radiator, which has a separation distance of LdandWd, respectively from the inner edge of the square-ring patch
radiator. With the presence of the square patch, the coupling between the simple microstrip feed line and the square patch can be enhanced and good impedance matching for obtaining circularly polarized radi-ation design can be easily obtained.
In order to reduce experimental cut-and-try design cycles, the simulation software HFSS is employed to guide fabrication. For conventional square-ring patch antennas, the fundamental resonant mode (TM11mode) occurs at a frequency whose wavelength in the square-ring corresponds approximately to the mean circumference of the square-ring [11]. That is
f =4(L 0 d 0 W=2)c p"
e (1)
"e = 1 + q("dr0 1) (2)
wherec is the speed of light in the free space, f is the fundamental fre-quency of the conventional square-ring antenna,4(L0d0W=2) is the mean circumference of the square-ring antenna,"e is the effective di-electric constant andq is the correction factor considering the presence of the different dielectric material on the two sides of the square-ring patch. In this study, square ceramic blocks of side lengthL = 15 mm and thicknessH = 3 mm were used in all measurements and the value ofq obtained from many simulations for the narrow ring width are sum-marized in Table I. It was found that the effective dielectric constant decreases when the ring width(W ) is increased.
III. OPERATIONALMECHANISM OFCP RADIATION
To achieve optimum performance, a parametric study is carried out using commercial EM software HFSS 10.0 to investigate the character-istics of the proposed square-ring antenna. The antenna’s initial values, unless otherwise stated, are fixed atLg= Wg= 30 mm, Wf = 3 mm, Lf = 9 mm, R = 3 mm, W = 0:8 mm, H = 3 mm, "dr= 58; L =
15 mm, Ls= 4:6 mm, Ws= 4:9 mm, Ld= 1:7 mm, Wd= 1:3 mm
and edge gapd = 0:5 mm. The calculated resonance frequency of the fundamentalTM11mode is approximately 1572 MHz.
IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 57, NO. 4, APRIL 2009 1267
Fig. 7. Measured and simulated antenna gain versus frequency for the proposed antenna.
has been designed, fabricated and found to have the bandwidth of 1.1% and 3-dB CP bandwidth of about 0.03% at the center frequency of 1573 MHz. By observing the radiation patterns, the 3-dB beam widths of about 90indicate the realization of a good circularly polarized char-acteristic. Measurements and simulations are in good agreement. In ad-dition, the proposed antenna has a small-sized, effective feeding struc-ture and an adequate CP bandwidth for commercial GPS applications.
ACKNOWLEDGMENT
The authors would like to thank the K.T. Li Foundation for the De-velopment of Science and Technology for the assistance with English grammar and usage.
REFERENCES
[1] J. R. James and P. S. Hall, Handbook of Microstrip Antenna. London, U.K.: Peter Peregrinus Ltd., 1989, vol. 1, ch. 4.
[2] Y. Suzuki, N. Miyano, and Y. Chiba, “Circularly polarized radiation from single-fed equilateral-triangular microstrip antenna,” Proc. IEE
Microw. Antennas Propagat., vol. 134, pp. 194–198, 1987.
[3] A. K. Bhattacharyya and L. Shafai, “A wider band microstrip antenna for circular polarization,” IEEE Trans. Antennas Propagat., vol. 36, no. 1, pp. 157–163, Jan. 1988.
[4] K. L. Wong and Y. F. Lin, “Circularly polarized microstrip antenna with a tuning stub,” Electron. Lett., vol. 34, pp. 831–832, Apr. 30, 1998.
[5] K. L. Wong, W. H. Hsu, and C. K. Wu, “Single-feed circularly polar-ized microstrip antenna with a slit,” Microw. Opt. Technol. Lett., vol. 18, pp. 306–308, Jul. 1998.
[6] H. M. Chen and K. L. Wong, “On the circular polarization operation of annular-ring microstrip antennas,” IEEE Trans. Antennas Propagat., vol. 47, no. 8, pp. 1289–1292, Aug. 1999.
[7] J. S. Row, “Dual-frequency circularly polarized annular-ring microstrip antenna,” Electron. Lett., vol. 40, no. 3, Feb. 5, 2004.
[8] A. Y. Simba, M. Yamamoto, T. Nojima, and K. Itoh, “Circu-larly polarised proximity-fed microstrip antenna with polarization switching ability,” IET Microw. Antennas Propag., vol. 1, pp. 658–665, 2007.
[9] D. C. Nascimento, R. Schildberg, and J. C. da S. Lacava, “New consid-erations in the design of low-cost pro-fed truncated corner microstrip antenna for GPS applications,” in Proc. 2007 IEEE AP-S Int. Symp., Honolulu, HI, Jul. 2007, pp. 749–752.
[10] J. S. Row, “Design of aperture-coupled annular-ring microstrip an-tennas for circular polarization,” IEEE Trans. Anan-tennas Propagat., vol. 53, pp. 1779–1784, May 2005.
[11] Y. S. Wu and F. J. Rosenbaum, “Mode chart for microstrip ring res-onators,” IEEE Trans. Microw. Theory Tech., vol. MTT-21, no. 7, pp. 487–489, Jul. 1973.
Printed Wideband Rhombus Slot Antenna With a Pair of Parasitic Strips for Multiband Applications
Jen-Yea Jan and Liang-Chin Wang
Abstract—In this paper, a printed microstrip-line-fed rhombus slot antenna with a pair of parasitic strips is presented. With the use of these parasitic elements along the microstrip feed line, bandwidth enhancement for wideband operation can be obtained. From experimental results, the measured impedance bandwidth, with a 10 dB return loss, can operate from 1.80 to 6.09 GHz which is wider than a conventional microstrip-line-fed printed rhombus slot antenna without parasitic elements. By selecting proper dimensions of parasitic strips, the proposed antenna can provide PCS, IMT-2000, and WiMAX multiband operations for various wireless communication services. Details of the proposed antenna are described, and experimental results are presented and discussed.
Index Terms—Bandwidth enhancement, microstrip-line-fed antennas, printed slot antennas.
I. INTRODUCTION
Printed slot antennas are attractive because of their wide impedance bandwidths, low cost, planar structures and easy integration with active devices or MMICs. Thus, great interest in various printed slot antennas can be seen in the literature. In recent years, some microstrip-line-fed printed slot antennas [1]–[5] have been reported because of their favor-able impedance characteristics. In the reported literature [5], a printed slot antenna with a fork-like tuning stub has been shown to have a good bandwidth enhancement. However, the structure of microstrip feed line used in [5] makes the configuration of the slot antenna more complicated. Another printed microstrip-line-fed slot antenna with a simple rotated slot for a wider bandwidth has also been studied in [6]. As a result, a wide operating bandwidth of about 2200 MHz (49.4%) with respect to the center frequency at 4453 MHz has been obtained. However, it is not enough for the operating bandwidth to cover more wireless communication services. In this paper, a new design of mi-crostrip-line-fed printed slot antenna with a pair of parasitic strips is proposed and investigated. In this design, a smaller ground plane is considered. By choosing proper dimensions of the ground plane and parasitic strips, it is seen that more resonant modes operating near the center frequency of the conventional slot antenna can be obtained. With these resonant modes, the proposed antenna can have similar radiation patterns and the same polarization. From the experimental results, the obtained impedance bandwidth (10 dB return loss) of the proposed an-tenna can operate from 1.80 to 6.09 GHz with a center frequency at around 4 GHz.
II. ANTENNACONFIGURATION
Fig. 1 shows the geometry and dimensions of the proposed mi-crostrip-line-fed slot antenna. According to the slot antenna design reported in [6], the printed slot of the proposed antenna selected is a rhombus shape. In order to excite more resonant modes for a wider operating bandwidth, a pair of parasitic elements is embedded in this
Manuscript received June 27, 2008; revised November 20, 2008. Current ver-sion published April 08, 2009. This work was supported in part by the National Science Council, Taiwan, under Contract NSC96-2221-E-151-002.
The authors are with the Department of Electronic Engineering, National Kaohsiung University of Applied Sciences, Kaohsiung 807, Taiwan (e-mail: [email protected]).
Color versions of one or more of the figures in this communication are avail-able online at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TAP.2009.2015859 0018-926X/$25.00 © 2009 IEEE
