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IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 50, NO. 3, MARCH 2002
A Small CP-Printed Antenna Using 120 Sequential Rotation Hing Kiu Kan and Rod B. Waterhouse
Abstract—We present a small printed antenna with broadband impedance and axial ratio (AR) characteristics. The antenna consists of three sequentially rotated shorted equilateral patches, with excitation phasings of 0 , 120 , and 240 , respectively. The measured 10-dB return loss and 3-dB AR bandwidths of the compact antenna are 31% and 27.5%, respectively. Index Terms—Circular polarization, microstrip antennas, mobile antennas, satellite navigation systems.
I. INTRODUCTION There are numerous military and commercial systems that require global position satellite (GPS) information for operation, such as several navigational aids. These applications typically need small, lightweight, low profile and nonobstructive antennas for the terrestrial terminals that can satisfy the necessary impedance and circular polarization (CP) bandwidth requirements. Recently, we introduced a small printed antenna that had reasonable impedance and CP characteristics [1]. The microstrip antenna consisted of four shorted patches [2], sequentially rotated and phase excited by 0 , 90, 180 , and 270 , respectively, applying the principles outlined in [3]–[5] to a small configuration. The developed antenna yielded impedance and 3-dB axial-ratio (AR) bandwidths of greater than 8.5% and was compact in size. It is interesting to note that of the many sequentially fed techniques (for example, two elements fed 0 and 90 , respectively, and so on), three elements fed 0 , 120 , and 240 , respectively, gives better voltage standing wave ratio (VSWR) and AR bandwidth that the other configurations [5]. The only possible drawback pointed out in [5] of the three-element synchronous subarray appropriate to the application here is the more complicated feed network to give the required power split. In this paper, we present a small printed antenna consisting of three shorted equilateral triangle patches sequentially rotated and excited by 0 , 120 , and 240 , respectively. The feed network providing the correct phasing is located below the ground-plane of the shorted patches and is etched on a high dielectric constant material to reduce its size. The measured 10 dB return loss and 3-dB AR bandwidths of the proposed small antenna are 31% and 27.5%, respectively, significantly greater than the small synchronous subarray presented in [1] and the relative bandwidth can easily accommodate the two GPS bands, needing 21% for the entire spectrum between the two bands. The overall dimensions of the new antenna are 0:30 2 0:30 2 0:080 , making the antenna compatible with the dimensions of small terminals for GPS receivers in the lower microwave frequency spectrum. The configuration layout and experimental impedance and radiation performance are given in this Letter. II. PROPOSED CONFIGURATION A schematic diagram of the sequentially fed subarray of shorted equilateral triangles is shown in Fig. 1. Shorted equilateral triangles Manuscript received May 23, 2001. The authors are with the School of Electrical and Computer Systems Engineering, RMIT University, Melbourne VIC 3001, Australia (e-mail:
[email protected]). Publisher Item Identifier S 0018-926X(02)02617-0.
Fig. 1. Schematic diagram of the three-element shorted patch synchronous subarray.
Fig. 2. Measured return loss and AR of the proposed small printed antenna 21 mm, x 0, y 8.1 mm, x (antenna parameters: L = 6.1 mm, x = 7.0 mm, y = 4.1 mm, x = 5.3 mm, y = 0; y 3.1 mm, x = 7.0 mm, y = 4.1 mm, x = 5.3 mm, and y = 3.1 mm).
0
=
0
=
=0 0
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were chosen as the radiating element due to the smaller size than rectangular and circular patches. Here, each of the three equilateral triangle patches of length, L is fed by a probe of radius r0 located at (xpi ; ypi ) relative to the center of the ith patch (i = 1, 2, 3). A shorting pin of radius r0s is positioned (xpsi ; ypsi ) from the center of each of the triangular-shaped patch conductors. The shorted triangular patches were designed using the methodology outlined in [6] and the software package Ensemble 5.1. The height of the substrate (d) used here is 10 mm. A thin layer of Taconic TLC30 ("r = 3.0 and d = 0.5 mm) is incorporated to etch the patch conductors. The patches are sequentially positioned and fed in a 0 , 120 , and 240 phasing arrangement and so the entire antenna demonstrates symmetry about boresight. A small gap (1–mm) exists between the apexes of the triangles. The feed network is similar to that presented in [1], although here a three-way power splitter was developed to ensure the correct magnitude distribution to each port. As in [1], to achieve the required phasing to the second and third patches, additional lengths of microstrip line were used. To minimize the size of the feed network, a high dielectric substrate was used (RT/Duroid 6010, "r = 10). A relatively thick substrate (2.5 mm)
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IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 50, NO. 3, MARCH 2002
399
of a user in close proximity to the antenna on its overall performance [7]. The gain of the antenna at 1.9 GHz was measured as 3.3 dBc. IV. CONCLUSION This paper has presented a small printed antenna with 10 dB return loss and 3-dB AR bandwidths in excess of 20%. The antenna consists of three sequentially rotated shorted triangular-shaped patches and a compact feed arrangement located below the ground-plane of the antenna. As a result of its broadband and compact features, the proposed antenna is very suited to small GPS terminals. Importantly too, the radiation pattern is very broad, another requirement for GPS terminals. REFERENCES
Fig. 3. Spinning linear radiation pattern of the proposed antenna at 1.9 GHz.
was chosen to ensure the widths of the feedlines are relatively thick, thus making the antenna robust. In a similar arrangement to that given in [1], pins of radius 0.6 mm were used to connect the short patches to the feed network. Shorting pins (r0s = 0.325 mm) were soldered between the patch conductors and the common ground-plane. An SMA connector is the input to the feed network and the substrates of both the antenna elements and the feed were truncated to give an antenna with the dimensions of 4.5 cm 2 4.5 cm. III. RESULTS Fig. 2 shows the measured return loss of the proposed three-element synchronous subarray. The 10-dB return loss bandwidth of the configuration is 31%. This is significantly greater than that recorded in [1], namely 8.5%, although a direct comparison is probably not appropriate as thicker materials relative to the operating frequency were used here. Despite this, the bandwidth is remarkably large for such a small antenna. These results are, however, consistent with the findings in [5], that is, three element synchronous subarrays improve the VSWR bandwidth by a factor of two or so essentially due to mismatch cancellation. The AR of the antenna at boresight was measured from 1.6 GHz to 2.5 GHz and the results are also displayed in Fig. 2. The measured 3-dB AR of the printed antenna is approximately 27.5%. Once again, the somewhat larger than expected AR bandwidths are consistent with the findings in [5] where it was postulated that the multiple reflections set up by the patches and feed mismatches radiate mainly reference polarization. It should be noted that the AR and impedance bandwidths do not exactly overlay, which is typical for most CP antennas. The common bandwidth is approximately 22%, consistent for requirements for coverage of both GPS bands. To achieve this frequency spectrum 40 MHz at 1.227 GHz as well as 40 MHz at 1.575 GHz, simple scaling of the antenna is required. Fig. 3 shows a measured spinning linear far-field radiation pattern of the proposed antenna at 1.9 GHz. It is evident from this plot that the truncated, symmetrical printed antenna provides excellent AR in most directions. This characteristic reduces the possible detrimental affect
[1] H. K. Kan and R. B. Waterhouse, “Small circularly polarized printed antenna,” Electron. Lett., vol. 36, pp. 393–394, Mar. 2000. [2] R. B. Waterhouse, “Small microstrip patch antenna,” Electron. Lett., vol. 31, pp. 604–605, Apr. 1995. [3] J. Huang, “A technique for an array to generate circular polarization with linearly polarized elements,” IEEE Trans. Antennas Propagat., vol. AP-34, pp. 1113–1124, Sept. 1986. [4] P. S. Hall, J. S. Dahele, and J. R. James, “Design principles of sequentially fed, wide bandwidth, circularly polarized microstrip antennas,” in Inst. Elect. Eng. Proc. H, vol. 136, Oct. 1989, pp. 381–389. [5] P. S. Hall, “Application of sequential feeding to wide bandwidth, circularly polarized microstrip patch arrays,” in Inst. Elect. Eng. Proc. H, vol. 136, Oct. 1989, pp. 390–398. [6] R. B. Waterhouse, S. D. Targonski, and D. M. Kokotoff, “Design and performance of small printed antennas,” IEEE Trans. Antennas Propagat., vol. 46, pp. 1629–1633, Nov. 1998. [7] M. A. Jensen and Y. Rahmat-Samii, “Performance of circularly polarized patch antennas for personal satellite communications including biological effects,” Proc. 1995 IEEE Antennas and Propagation Symp., pp. 1112–1115, June 1995.
Broad-Band Dual-Polarized Single Microstrip Patch Antenna With High Isolation and Low Cross Polarization Tzung-Wern Chiou and Kin-Lu Wong Abstract—This paper presents a new design of a broad-band dual-polarized single microstrip patch antenna with highly decoupled input ports and low cross-polarization (XP) radiation. A prototype of the proposed antenna with center frequency at 1800 MHz is presented. Both the dual linear polarizations have 10-dB return-loss impedance bandwidths greater than 14% and high decoupling between the two input ports ( less than 40 dB across the entire bandwidths) is obtained. Moreover, the XP radiation in the principal planes of the dual linear polarizations is seen to be less than 20 dB. Index Terms—Broad-band patch antenna, dual polarized patch antenna.
I. INTRODUCTION Obtaining high isolation between two input ports and low cross polarization for dual linear polarizations is an important problem and also a challenge to antenna engineers in the design of dualManuscript received March 6, 2000; revised November 22, 2000. The authors are with the Department of Electrical Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan 804, R.O.C. Publisher Item Identifier S 0018-926X(02)04572-6.
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