Majlesi Journal of Electrical Engineering Vol. 10, No. 2, June 2016 1 Omnidirectional UWB Monopole Antenna with WLAN Notched-band Functionality Zahra Bastani 1,2 , Mohamad Amin Honarvar 3* , Masoud Jabari 4 1-Department of Engineering and Technology, Fars Science and Research Branch, Islamic Azad University, Shiraz, Iran 2-Department of Engineering and Technology, Shiraz Branch, Islamic Azad University, Shiraz, Iran Email: bastani_eng@yahoo.com 3-Department of Electrical Engineering, Najafabad Branch, Islamic Azad University, Najafabad, Iran Email:Amin.Honarvar@gmail.com (Corresponding Author) 4-Department of Electrical Engineering, Marvdasht Branch, Islamic Azad University, Marvdasht, Iran Email: jabari@miau.ac.ir Received: June 2015 Revised: July 2015 Accepted: August 2015 ABSTRACT: This paper introduces a novel ultra-wideband (UWB) microstrip antenna having wireless local area network band rejection characteristics. The proposed antenna is composed of a lip-shaped radiation patch being fed by a 50 Ω coplanar waveguide (CPW) feed line. The ground vertically continued to the two sides of the radiator. Thus, the substantial extra space adjacent to the radiator can be efficiently saved. The band rejection in the wireless local area networks (WLAN) (5.15-5.825GHz) is secured through etching the two symmetric C-shaped slots on ground plane to preclude interference between UWB and WLAN systems. The proposed antenna is of the size of 30×30×1.6 3 working within the range of 2.9 to 11.2 GHz with VSWR lower than 2 except in 5.15-5.825GHz band. Finally, the antenna is simulated and fabricated with nearly omnidirectional radiation patterns, stable gain and constant group delay in the operating band. KEYWORDS: Ultra-wideband (UWB), Coplanar waveguide (CPW), Microstrip antenna, Wireless local area network (WLAN), Voltage standing wave ratio (VSWR). 1. INTRODUCTION In order to make the ultra-wideband (UWB) technology useful for the community and to prevent possible interference to other existing electronic systems, the Federal Communications Commission (FCC) published the first report and order on February 14, 2002 [1]. The order deals with the employment of UWB systems within the 3.1-10.6 GHz band. Because of such useful characteristics as low cost, unsophisticated structure, ease of construction, low profile, high data rate, and nearly omnidirectional radiation pattern, the UWB microstrip antennas have attracted the attention of both academia and industry [2]. Since conventional antenna theory is based on the narrow band assumption and cannot be used to design UWB antenna, novel techniques and technologies need to be developed for UWB antenna design. Furthermore, within the UWB operation band, existing narrowband communication systems, such as 5.15–5.825 GHz band (IEEE 802.11a) wireless local area networks (WLAN) may cause electro-magnetic interference to UWB applications. To remedy this situation, several band-notched techniques have been proposed in UWB antennas [3-8]. In the present research, an UWB microstrip antenna having WLAN band rejection characteristics is introduced. The design is formed on the basis of a lip-shaped radiation patch. In this paper, we propose a simple and compact CPW-fed UWB antenna with band-notched characteristics in 5-6 GHz. To achieve wide band characteristic, tapered ground plane is used. The WLAN band rejection is achieved through etching two symmetric C-shaped slots on the ground plane. The results emanating from simulation and measurement of the proposed antenna are indicative of the fact that the voltage standing wave ratio (VSWR) is capable of successfully covering the UWB spectrum. Nearly omnidirectional radiation patterns, constant group delay, stable gain and satisfactory agreement between the measured and the simulated results are obtained from this research. The antenna has dimensions of 30×30 mm 2 , which is compatible with the requirements imposed by portable systems. The overall size of the proposed structure is smaller than many other researches [9-14]. The proposed antenna operates within the 2.9 to 11.2 GHz frequency band as VSWR < 2 except a stop-band of 5.15-5.825GHz, which is a suitable candidate for UWB communication systems.