ILLUSTRATIVE DESGINS OF MULTIBAND, WIDEBAND AND EBG-ENHANCED ANTENNAS

Raj Mittra

Electromagnetic Communication Laboratory

Pennsylvania State University

University Park, PA, USA

The purpose of this paper is to review a number of innovative design concepts for multiband, wideband and EBG-enhanced planar antennas that find a variety of applications in voice and data communication, as well as in GPS. We begin by discussing two novel multiband antenna designs for multiple frequency applications. The first of these, which is based on fractal concepts, is a Sierpinski gasket type of fractal configuration, printed on a dielectric substrate backed by a ground plane. We then describe an approach to enhancing its multiband performance, in terms of impedance matching characteristics as well as radiation patterns, at three operating frequencies. The second design combines a rectangular microstrip patch with a cylindrical dielectric resonator, and operates at multiple frequencies. Specifically, we describe a stacked configuration of a dielectric resonator antenna on a microstrip patch for three frequency bands. Circular polarization is obtained by utilizing four coax feeds in phase quadrature. This configuration is found to exhibit good cross-pol rejection characteristics.

Recently, there has been a great deal of interest in the design of antennas for wireless communication because of continuously expanding range of wireless telecommunication services and related applications for voice and data transmission. To realize a high data rate of wireless transmission such as Ultra Wide Band (UWB) communication, it is necessary to use a wideband antenna, and to suppress the interference signals in this band with a notch filter. If the antenna package is to be installed in a portable wireless computer and communication system, the package must be compact in size. Bearing this in mind, we proceed next to describe two antenna designs that are suitable for such applications. The first of these is a configuration which we call the planar volcano-smoke slot antenna (PVSA), which comprises a planar slot¾with an appearance reminiscent of a volcanic crater and a puff of smoke¾and is fed by a coplanar waveguide (CPW) to achieve the wide bandwidth. We demonstrate that with a suitable design, we can achieve an impedance bandwidth between 0.8 and 6.7 GHz (for a VSWR < 2.3) and a pattern bandwidth ranging from 0.8 GHz to 2.0 GHz for the radiation in the upper hemisphere. In addition, we present the design of an absorber-backed PVSA to suppress the radiation along the side- and back-directions.

Next we describe a dual-band antenna design useful for Wireless Local Area Network (WLAN) applications, both in the 2.4 GHz band (2.39 – 2.49 GHz) of IEEE 802.11b/g, as well as for the 5 GHz band (4.9 – 5.1 GHz, 5.15 – 5.35 GHz and 5.47 – 5.9 GHz) of IEEE 802.11a. Several different types of dual-band antennas with a single feed have been investigated in the past that offer a low cost and compact design. Since the radiation pattern characteristics of a WLAN antenna for notebook platforms are affected by the location where it is mounted, the design of such antennas indeed presents quite a challenge.

Finally, to round out the discussion, we turn to EBG-enhance design, a topic which has attracted much recent attention among researchers working in the microwave regime. It is well known that, at microwave frequencies, EBG materials are artificial dielectrics that comprise of a periodic array of metallic or dielectric elements, which exhibit stop- and pass-band characteristics. It is also possible to deliberately introduce defects in the periodic structures of the EBG materials by breaking up the periodicity, and inducing localized frequency windows within the forbidden frequency band (bandgap) in the process. In this paper, we show how both of these types of EBGS can be used to our advantage to enhance the performance of planar antennas by improving their impedance as well as radiation pattern characteristics. We consider periodic dielectric structures, as well as Frequency Selective Surfaces (FSSs) embedded in a background dielectric medium, which may be multilayered.

Extensive set of results, which serve to illustrate the implementation of the different design concepts mentioned above, will be included in the presentation.

Acknowledgement: The authors is grateful to several former and present members of the EMC Lab, including Dr. Junho Yeo, presently with ETRI in Korea, Mr. Young-Ju Lee and Prof. WeeSang Park of Pohang University also in Korea, as well as Mr. Yoonjae Lee of CRS in Virginia (USA), whose pioneering and seminal contributions are extensively featured in this review paper.