INTERNATIONAL JOURNAL OF SCIENTIFIC & TECHNOLOGY RESEARCH VOLUME 9, ISSUE 01, JANUARY 2020 ISSN 2277-8616 1573 IJSTR©2020 www.ijstr.org An Ultra-Wide Band Octagonal Antenna With Reconfigurable Narrowband Antenna For Cognitive Radio Applications Buddi Bhanu Shankar, Dasari Anantha Sai Kumar, Garlapati Venkata Kowndinya, Arjuna Muduli, Deepak Kumar Nayak Abstract: The idea of this paper is to design a dual port ultra-wide band antenna integrated with reconfigurable narrow band antenna for cognitive radio applications. The narrow band antenna is a microstrip patch antenna attached at the back side of the ultra-wide band octagonal antenna. The ultra-wide band senses over the frequency range of 3.91 – 11.29 GHz. The Narrowband reconfigurable antenna is seen to operate at 6.39GHz, 6.90GHz, 7.81GHz, 8.94 GHz. Isolation between both the ports is kept less than -15 dB over entire operating band. Reconfiguration is done with the help of pin diode. The antenna switched from ultra-wide band to narrow band by switching ‗ON‘ the pin diode. Keywords: Cognitive radio, ultra-wide band, narrowband, return loss ———————————————————— I. INTRODUCTION A cognitive radio represents an innovative approach to wireless communications where they can sense, monitor and dynamically reconfigure according to the requirement. This was first introduced by Joseph Mitola in 1999. It can identify unused gaps in spectrum and use them, as they are self-learning and adaptable based on the previous knowledge. The objective of Cognitive Radio (CR) is to reduce the dependency on a single channel spectrum by implementing cognitive radio approach and to utilise available communication channels more efficiently. A cognitive radio network must be able to sense the available spectrum and the gaps in it which is performed by the ultra- wide band antenna. The UWB antenna should have large bandwidth with an omni-directional radiation pattern to make sensing of the complete spectrum swiftly and depending on the requirements narrowband sensing also performed. A CR antenna can be realised in two ways to perform both sensing of spectrum and switching of spectrum: (a)integrating a narrowband (NB) antenna into an ultrawideband (UWB) antenna, and (b) a single UWB antenna performing both operations. The integrated CR antenna provides multi-role actions in single module, and it is suitable for a compatible device where available space is restricted. In this paper, the ultra-wide band is chosen as octagonal patch whose operating frequency is from 3.91 – 11.29 GHz having a partial ground. At the back side of the octagonal antenna, another microstrip antenna that is rectangular in shape is designed which is a reconfigurable narrowband antenna that is used for spectrum selection, meaning it selects the gaps found by the Ultra-wide band antenna. The Cognitive Radio is applied on the all the wireless applications such as cellular phones, tv broadcasting, defence applications, TV white spaces, Opportunistic cognitive radio networking, emergency and public safety applications, Vehicular Communications, Operator-controlled/assisted CR networks. I. DESIGN OF ANTENNA Fig.1 Front and back side of proposed design The above figure shows an Octagonal patch ultra-wide band antenna designed in CST Microwave Studio whose operating frequency is from 3.91 GHz to 11.29 GHz. It is printed on FR-4 substrate of dimensions 40mmX50mm, whose dielectric constant (Ꜫ r ) = 4.4 and thickness of the substrate of 1.6mm. The feedline of Octagonal patch is of length 16mm and width 2.6mm. At the back of this antenna there is a partial ground and reconfigurable narrow band antenna (rectangular patch antenna). The dimensions of this rectangular patch are chosen in order to produce sufficient gain as well as have considerable isolation with the octagonal microstrip antenna. The reconfiguration is done by using three PIN diodes which act as variable resistors. The Narrow band antenna operates in different bands, depending on the switching conditions. However, the reconfiguration in simulation is performed by adding resistors for which three slots of 0.2 mm width are cut at different location of the microstrip feed line. These cuts are then joined using lumped elements and sufficient values of the resistance will determine the switching conditions where we get unique gain pattern for each. The parameters of the structure are as follows: ___________________  Buddi Bhanushankar, ECE, B.Tech, Koneru Lakshmaiah Education Foundation,Guntur. AP  Dasari Anantha Sai Kumar , ECE, B.Tech, Koneru Lakshmaiah Education Foundation, Guntur, AP  Garlapati Venkata Kowndinya, ECE, B.Tech, Koneru Lakshmaiah Education Foundation, Guntur.,AP  Arjuna Muduli, Assoc. Professor, Department of ECE, Koneru Lakshmaiah Education Foundation,Guntur,AP.  Deepak Kumar Nayak, Assoc. Professor, Department of ECE, Koneru Lakshmaiah Education Foundation, Guntur,AP