Antenna Systems & Technology - Spring 2012 - (Page 26)

FEATURE ARTICLE Efficient Design and Analysis of an Ultra Wideband Planar Antenna with Band Rejection in WLAN Frequencies By ElectromagneticWorks, Inc. and LACIME LAB The telecommunication industry continues to move towards transferring larger and larger amounts of data in the shortest possible time using wireless technology. To accomplish this goal, it is necessary to operate at higher frequencies and to utilize larger bandwidths. Originally, the main purpose of designing ultra wide band antennas was to fulfill the requirements of radar related systems like the systems used for snow measurement [1]. Using UWB technology was an inexpensive way to design Snow Depth Sensors (SDS) and also Snow Water Equivalent (SWE) measuring systems [1]. Many such radar applications motivated the Federal Communication Commission (FCC) to allocate the 3.1 GHz to 10.6 GHz frequency band to Ultra Wideband devices. This allocation was the starting point for many of innovations based on wide band communications and data transfer. Today, localized communications demand an Ultra-Wideband to enable the transfer of massive data, such as high resolution multimedia content, which is critical in many applications such as hostile environments monitoring systems, hi-tech surgeries and underground communications [2, 3]. Different antenna designs have been proposed to cover the FCC ultra wideband, but two major challenges have always existed for UWB antenna designers: keeping the low profile of the antenna to make it possible to be integrated in portable devices, and dealing with the interference from wireless LAN devices operating at 5.8 GHz. In this article we propose a printed ultra wide band antenna with a band rejection at WLAN frequencies in order to address both challenges. We also propose an efficient procedure to design and optimize such antennas using a sophisticated high frequency simulator, HFWorks [4]. The proposed antenna is a wineglass-shaped monopole slot fed with a Coplanar Waveguide line. In order to achieve to a band notch at 5.8 GHz, a narrow circular slit has been etched on the radiating element, which creates an open circuit and prevents antenna from radiation at that particular frequency range. Antenna Design As mentioned, the antenna proposed here is a microstrip patch antenna fed with a coplanar waveguide (CPW). The radiating element of the antenna is formed of two semicircles; one metallic one and one slot etched on the ground of the coplanar waveguide. The metallic semicircle is the exciting element for the slot semicircles that leads to the radiation of the aperture. The combination of the two semicircles with the CPW line creates a wineglass shaped configuration. This configuration works like a monopole antenna which, when properly dimensioned as in figure 1a, can achieve a bandwidth that covers the whole FCC band, namely from 3.1 GHz to 10.6 GHz. In [5, 6] and [7], it is suggested to use the following formula to find the approximate aperture size of circular ultra wideband antennas: (1) where Ruwb is the radius of the aperture, c is the speed of light, εreff is the effective dielectric constant and f is the lowest frequency of the band, i.e., 3.1 GHz in this case. As the frequency increases, we can see that the radius of the aperture decreases and this is the basic idea behind the ability of the antenna to operate in such a wideband, because the radiating circles will be formed hypothetically inside the main circle. However, in the proposed design, the story is slightly different, indeed, in order to keep the lowest possible profile by using semicircle instead of the full circle, the mentioned formula would not give us the exact radius. Therefore, finding the correct geometry requires an optimization. The optimization for the proposed antenna has been performed using the high frequency simulator, HFWorks. Using the simulator’s built-in multi-configuration tool, a design table has been defined to take different values for the radii of both semicircles, Ruwb and Br. Then using the multistudy interface, the design was optimized to fulfill the FCC band requirements. The results of the optimization process are given in Table 1. Ruwb (mm) 40 Br (mm) Substrate Thickness (mm) 0.79 Permittivity 12 3.48 Table 1. General Dimensions of the UWB Antenna Figure 1 . The UWB antenna (a) The original configuration (b) The proposed configuration (c) The parasitic slit parameters The next step is to design a sort of filter in order to perform the band rejection in WLAN frequencies. To accomplish this, we can either suppress the metallic semicircle at a certain radius by etching a parasitic slit or suppress the slot semicircle by printing a metallic parasitic arc. 26 ANTENNA SYSTEMS & TECHNOLOGY SPRING 2012 WWW.ANTENNASONLINE.COM http://WWW.ANTENNASONLINE.COM

Table of Contents for the Digital Edition of Antenna Systems & Technology - Spring 2012

Antenna Systems & Technology - Spring 2012
Editor’s Choice
Next-Gen Networks Call for the Re-Architecture of Antenna Systems
Wireless Infrastructure Cable and Antenna Testing Using the Next-Generation in Handheld Measurement Tools
Antenna Upgrade Challenges in Concealed Cell Towers
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Wireless Communication
Test & Measurement
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Efficient Design and Analysis of an Ultra Wideband Planar Antenna with Band Rejection in WLAN Frequencies

Antenna Systems & Technology - Spring 2012