Large 2D Scatterers,’’ 11th Annual Re¨ iew of Progress in Applied Computational Electromagnetics, p. 606, 1995. S. Stein, ‘‘Addition Theorems for Spherical Wave Functions,’’ Q. Appl. Math., Vol. 19, No. 1, 1961, pp. 15 24. W. C. Chew, Wa¨ es and Fields in Inhomogeneous Media, Van Nostrand Reinhold, New York, 1990, reprinted by IEEE Press, 1995. W. K. Tung, Group Theory in Physics, World Scientiﬁc Publishing Co., Singapore, 1984. J. A. Stratton, Electromagnetic Theory, McGraw-Hill, New York, 1941.
this article, and characteristics of the antenna are experimentally investigated. 2. DESIGN CONSIDERATIONS AND EXPERIMENTAL RESULTS
1997 John Wiley & Sons, Inc. CCC 0895-2477r97
A COMPACT MEANDERED CIRCULAR MICROSTRIP ANTENNA WITH A SHORTING PIN 1
Kin-Lu Wong,1 Chia-Luan Tang,1 and Hong-Twu Chen 2 Department of Electrical Engineering National Sun Yat-Sen University Kaohsiung, Taiwan 804, Republic of China 2 Department of Electrical Engineering Chinese Military Academy Fong-Shan, Taiwan 830, Republic of China Recei¨ ed 8 January 1997 ABSTRACT: By using a shorting pin and meandering the circular patch, a compact circular microstrip antenna with a patch size of less than 10% of the con¨ entional circular patch antenna can be easily obtained. The design of such compact circular microstrip antennas is described, and experimental results are presented and discussed. 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 15: 147 149, 1997 Key words: compact circular microstrip antenna; meandered circular patch; shorting pin 1. INTRODUCTION
Figure 1 shows the conﬁguration of the short-circuited, meandered circular microstrip antenna. The circular patch is short-circuited at the edge with a shorting pin, and three narrow slots of the same length Ž l . and width Ž w . are cut in the patch. The shorting pin makes the circular patch resonate at a much lower frequency w2x, as compared with a conventional circular patch of the same size. The narrow slots meander the patch and thus increase the effective electrical length of the patch. These two factors effectively reduce the required disk size for the antenna to be operated at a given frequency. Based on this design concept, the short-circuited circular microstrip antennas with different slot lengths were constructed. The circular patch has a radius Ž d . of 7.5 mm, and a shorting pin of radius Ž r s . 0.4 mm is placed near the patch edge at R s d s s 6.5 mm. The patch substrate has a dielectric constant Ž r . of 4.25 and a thickness Ž h. of 1.6 mm. Figure 2 shows the measured resonant frequency versus the slot length in the short-circuited circular patch. Results clearly indicate that, with increasing slot length, the resonant frequency of the meandered patch decreases. It is also found that the slot width has relatively little effect on the resonant frequency. From the results for the case of l s d, the circular patch of radius 7.5 mm has a resonant frequency as low as 1.652 GHz. As for a conventional circular patch antenna Žwithout a shorting pin and the slots in the patch., the radius of the circular patch to be operated at 1.652 GHz needs to be about 25.2 mm Žwith the same substrate material.. That is, the patch size is reduced to be about 9%, as compared with the conventional circular patch of the same operating frequency. When the slot length increases, the resonant frequency of the patch can be reduced further, which can reduce the patch size even further at a given frequency. The return loss for the case l s d is plotted in Figure 3. In order to obtain a good matching condition, the feed position is placed close to the shorting pin. When the feed position is away from the shorting pin, the resonant input resistance is
Because of the miniaturization of personal communication equipment, the demand for small antennas has increased. To meet such a requirement, several designs of the compact microstrip antennas have recently been proposed w1x. One of...