Design & Analyzes of Dual-Frequency Circular Microstrip Patch Antenna with a Shorting Pin Sultan Can 1 , K. Yavuz Kapusuz 2 , and Elif Aydın 3 , Atilim University, Department of Electrical & Electronics Engineering Ankara, Turkey sultancan@atilim.edu.tr 1 , kapusuz.kyavuz@student.atilim.edu.tr 2 , eaydin@atilim.edu.tr 3 Abstract— In this study, several circular microstrip antennas are examined, which are also commonly referred to as the patch antennas. The operating frequencies of these antennas are determined for different radius, thickness and permittivity values. The effect of the position of the shorting pin also analyzed. Resonant frequencies of the circular patch antennas are investigated by changing the antenna parameters, which are radius of the circular patch (d), permittivity ( r ), thickness (h), placement of the radius of the shorting pin over radius of the patch (d S /d) and frequency ratio (r). Different antennas are proposed and among those, highest frequency ratio is obtained by changing the parameters of the antenna in the available literature. The maximum frequency ratio is achieved which is 7.13. The results are compared with the ones in literature and average error is also presented. Keywords; Dual-frequency, circular patch antenna, shorting pin loaded microstrip antenna, resonant frequencies I. INTRODUCTION Antennas are the most important elements for wireless communication systems [1]-[12]. They are suitable for aircraft, satellite and missile applications where size, weight, ease of installation, mechanical reliability and cost are required [2]. The microstrip antennas are low profile, mechanically robust and inexpensive to manufacture [8]. Moreover, microstrip patch antennas are compatible with integrated circuit designs and they are relatively light and compact. One of the most important ways to achieve high efficiency in a communication system is increasing the efficiency of the antenna. Since the efficient design of a patch antenna is crucial, calculating design parameters such as resonant frequency and input impedance is getting more and more important [5]-[6]. The studies in the literature, which presents calculation of resonant frequency and input impedance, are based on curve fitting [4]. To calculate these parameters, an accurate curve fitting has to be done and this process is achievable by analyzing more antennas with different parameters. The microstrip antennas also allow the use of additional tuning elements like shorting pins, stubs, notches or varactor diodes between the patch and the ground plane to get the dual-frequency operations [2]. Inserting a shorting pin is one of the most efficient ways to form dual operation since it significantly reduces the antenna size [2]- [4]. Besides this advantage, inserting a shorting pin to a circular patch is preferred because the studies in literature show that shorting pin loaded circular antennas have larger frequency ratios when compared to the rectangular ones [4]. Another advantage is that, although these antennas have dual frequency, the polarization for each frequency is the same and also they have the same broadside radiation pattern [11].In this study, resonant frequency values are obtained for different radius values of the shorting pin loaded circular microstrip patch antenna. Furthermore, various high frequency ratios are achieved by changing permittivity values, ratio between placements of the radius of the shorting pin, patch radius, and thickness values. II. ANTENNA DESIGN The proposed antenna configuration is shown in Figure 1. The antenna is fed by coaxial cable, and it has a shorting pin. The circular patch, printed on a substrate of a thickness h, and permittivity  r , has a radius d. The distance of the shorting pin position and feed point from the center of the circular patch is represented d s and d f , respectively. Figure 1. Geometry of a circular patch antenna with a shorting pin d f h Substrate Coax Shorting pin d s d