In this paper, a novel Microstrip Fractal patch antenna with dual polarization, which operates in a frequency band of 2-4 GHz (S-band) is proposed. Two challenging issues in the design of dual polarized antennas are obtaining high isolations and low cross polarized levels. Here we propose a technique to overcome these drawbacks by making use of the fractal geometry. The use of fractal geometry will improve bandwidth and reduce isolation loss. These geometries can also improve impedance matching. The proposed fractal antenna shows multiband characteristics by which the bandwidth can be improved. Sierpinski carpet fractal structure is used which shows high isolation compared to conventional dual patch antenna. Simulations are done by using Ansoft High Frequency Structure Simulator (HFSS) software. The proposed antenna finds its application in weather radars, communication satellites and wireless communications with improved bandwidth.

An Electric Ring Resonator (ERR) loaded Sierpinski Square Gasket Fractal (SSGF) antenna for multiple frequency band application is proposed, fabricated, and measured. The CPW-fed antenna consists of a Multi-mode Electric Ring Resonator (MERR) which is fixed on reverse side of the substrate and iterated Sierpinski gasket fractal derived from a square patch which is stamped on top of an FR4. Multi-bands can be obtained by placing a single multi-mode ERR beneath the CPW structure of the antenna. Each resonating frequency band can be easily tuned by properly changing the dimensions of the ERR structure. Instead of ERR's quasi-lumped capacitance, reconfigurability of the low, middle, and high frequency bands can be achieved by using a pair of Digital Variable Capacitors (DVCs) inserted into the middle of the ERR's rings corresponding to the chosen mode. The bandwidth is enhanced using four iterations of square radiating patch, modified feed line, and multi-mode electric ring resonator-loaded ground plane. More specifically, the impedance matching of the CPW fed antenna is improved by introducing transitions between the microstrip feed line and the Sierpinski square gasket. The numerical results show that the proposed antenna has good impedance bandwidth and radiation characteristics in the operating bands at 3.08/5.81/8.02/12.13/15.56 GHz which cover the frequency spectrum of WiMAX, WiFi/WLAN(IEEE 802.11a), IEEE 802.16e, X-band uplink, S/C/X/Ku and K band with return loss of better than 10 dB.

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