A NOVEL POLYGON ANTENNA SCANNED ARRAY FOR COGNITIVE RADIO INTRODUCTION The need for higher data rates is increasing as a result of the transition from voice only communications to multimedia type applications. Given the limitations of natural frequency spectrum, it becomes obvious that the current statistic frequency allocation schemes cannot accommodate the requirements of an increasing number of higher data rate devices.[1] Cognitive radio arises to tempting solution to the spectral congestion problem by introducing opportunistic usage of the frequency bands that are not heavily occupied by the licensed users. According to the Federal Communications Commission (FCC), a cognitive radio is “a radio that can change its transmitter parameters based on interaction with the environment in which it operates” [2].A device able to receive or transmit electromagnetic energy is called an 'antenna'. The antenna plays the role of a transitional structure between free space and a guiding device. In a wideband circular monopole and a narrowband dipole antenna for cognitive radio were presented with bandwidth of the wideband monopole antenna is from 5- 12GHz and narrowband dipole antenna's central frequencies are 7GHz and 9.77GHz. In [3] wideband, multi- band or reconfigurable antennas have been developed and when considering the interference levels at the receiver, reconfigurable antennas are the best option, since only one single band is used at a given time. This paper presents two different antennas which have been By developed to address the specific demands of portable cognitive radio handsets. Each antenna combines UWB and narrowband functionality within a small space. A compact, CPW-fed polygon shape aperture antenna for lower band UWB applications is presented. This antenna consists of a polygon aperture on a printed circuit board, ground plane and a polygon-shaped exciting stub. Initially the proposed antenna is designed with rectangular aperture and then the rectangular shaped aperture is converted into polygon shaped aperture by inserting a isosceles right angled triangular metallic shape in the corners of rectangular aperture to increase the impedance matching in the required bandwidth. [4]The polygon aperture (slot) is simple and has less parameter, which is convenient to optimize. The proposed antenna is designed on an inexpensive FR4-epoxy substrate. To achieve the desired properties one may select one of the many design data sets with a trade-off between broadband property and directivity. In [5] a new reconfigurable antenna is designed for Cognitive Radio. It consists of two structures incorporated together into the same substrate. In [6] a high broad side gain MEMS based reconfigurable antenna was designed for four frequency bands. A new family of microstrip-fed Ultra-Wideband (UWB) antennas with multiple (triple/quadruple) notched bands is proposed. The notched bands are generated by a band notched filter composed of double Stepped Impedance Resonators (SIRs) [7]. A polarization reconfigurable antenna *-** Sathyabama University, Chennai, India. ABSTRACT This paper presents about a new antenna design of ultra wide band antenna for cognitive radio wireless communication. This antenna consists of polygon on a printed circuit board; ground plane .This antenna was simulated in ADS (Advanced Design System) Momentum. The feeding point is the micro strip line and to this attached the polygon structure. A ultra wideband antenna is necessary in order to achieve the channel sensing which should possess an Omni directional radiation pattern. The ultra wide band antenna covers a spectrum from 5GHz to 12GHz for channel sensing. The resonant frequencies of the antenna are 7GHz and 9.77GHz. Keywords: Cognitive Radio, Micro-Strip Patch, Polygon Patch, Sensing Antenna. C.D SURIYAKALA ** S. SIVA SUNDARA PANDIAN * RESEARCH PAPERS 15 l i-manager’s Journal on Communication Engineering and Systems Vol. No. 4 12 l , 1 August - October 20