1814 PIERS Proceedings, Kuala Lumpur, MALAYSIA, March 27–30, 2012 A Single Feed Circularly Polarized Wallis Sieve Fractal Microstrip Antenna V. Venkateshwar Reddy and N. V. S. N. Sarma National Institute of Technology, Warangal, India Abstract— A new type of compact circularly polarized single feed microstrip antenna is pre- sented. In order to achieve the specified characteristics Wallis sieve fractal geometry is employed. Simulated results indicate that the proposed antenna gives a very good circular polarization with minimum axial ratio very close to 0 dB at the center frequency of 2430 MHz and impedance bandwidth (at 10 dB reference) of 4.25%. The antenna provides almost constant gain of about 3.2 dBi over the frequency band of operation. This antenna can be used in WLAN, Bluetooth and WiMAX, Wi-Fi etc at ISM band. The antenna can also be used for multiband opearation. 1. INTRODUCTION Microstrip patch antennas are small size, low profile antennas. Circularly polarized microstrip antennas find applications in different fields like WLAN, GPS, Mobile satellite, RFID applications etc. It is required to design antennas with compact size without degradation in gain of the antenna in the said applications. The circular polarization can be obtained by exciting two near degenerate modes which are orthogonal to each other. The conventional method of getting circular polarization is by the use of nearly square patch or square patch with diagonal slot. Those methods give 6 dB axial ratio bandwidth not more than 1%. There are many methods reported in the literature with single feed circularly polarized antennas using square patch. The first single feed CP antennas are reported by P. C. Sharma and K. C. Gupta [2] using square patch with truncated corners and square patch with inclined slot. But the obtained 6 dB axial ratio bandwidth is only 0.831% and 1.134% respectively with those antennas. M. L. Wong etal. [3] presented a different method to get circular polarization mainly aiming for compact size by incorporating slots and adding tails to the square patch. But with that method the impedance and 3 dB axial ratio bandwidths are 1.61% and 0.381% respectively. J. S. Rowand and C. Y. Ai [4] have proposed a compact design of single feed circular polarized antenna by cutting a crossed slot on the circular patch backed by square shaped ground plane with crossed slot. But the peak gain is very low which is in the order of 1.8 dBi and 3 dB axial ratio bandwidth is around 0.9%. M. Elsdon et al. [5] have published work on a single feed star loaded patch antenna for circular polarization with 3 dB axial ratio bandwidth at 2.4 GHz around 1.1%. The input impedance of the patch varies from 245 ohms to 705 ohms. Wen-Shyang Chen etal. [6] have presented a novel compact circularly polarized square microstrip antenna. The gain variation with that antenna is only 1.4dBi to 3.5dBi. Kin-Lu Wong and Jian-Yi Wu [7] have proposed a single feed circularly polarized microstrip antenna by providing two pairs of narrow slits in the x and y directions of the square patch. It is not clear whether the methods mentioned above give 0dB axial ratio at the center frequency. However there is a need to design a circularly polarized antenna which provides 0dB axial ratio at the center frequency and should give at least 3 dB axial ratio bandwidth of 1%. Further the antenna should be perfectly matched to the line. In the present paper a novel technique is used to get circular polarization by the use of fractal antenna which not only has all the above qualities but also compact in size. 2. ANTENNA GEOMETRY The proposed wallis sieve fractal antenna to be operated at 2.5 GHz can be realized by introducing slots on the square patch with size 6 × 6 mm 2 in iteration 1, 6 × 6 mm 2 and 2 × 2 mm 2 slots in iteration 2. The generation of the fractal Antennas is shown in Figures 1–4. Two cases have been considered in this paper: first one is linearly polarized wallis sieve fractal antenna and the second one is circularly polarized antenna. The size of the patch is 36 × 36 and is printed on RT Duroid substrate of thickness 1.6mm with relative permittivity of 2.75. The antennas are simulated using Zeland IE3D electromagnetic simulator. For linearly polarized case the antennas are with transmission line feeding at point (-18, 0) and keeping electrical length constant in both sides. In this case the behavior of the antenna for three iterations is studied. The geometries of the antenna are shown in Figures 1–4. The resonant frequency of the antenna is changed from 2493 MHz to