96 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 14, 2015 Antipodal Fermi Tapered Slot Antenna for 60-GHz Band Applications Issa Mohamed, Zouhair Briqech, Student Member, IEEE, and Abdelrazik Sebak, Fellow, IEEE Abstract—A 60-GHz antipodal Fermi tapered slot antenna (AFTSA) with sine corrugation is presented. It exhibits a flat measured gain of 18.8 dB with return loss better than 18 dB over a frequency range of 55–65 GHz. To further improve the antenna’s performance, two other shape-modified AFTSAs are presented: one with a delta-shaped slot and the other with a dia- mond-shaped slot and loaded with an elliptical-shaped dielectric. The diamond-shaped slot modified antenna maintains a measured gain of 20 dB with return loss better than 22 dB over the entire band. The overall efficiency is 93%. Good agreement between simulated and measured results is obtained. Index Terms—60 GHz, antipodal tapered slot antenna, dielectric loading, wideband antenna. I. INTRODUCTION R ECENTLY, there is a high interest in developing multi- gigabit-per-second short-range wireless systems due to consumer demand for high-data-rate services. Although the large unlicensed spectrum around 60 GHz is the best candidate to support these wireless systems, it suffers from a high atmo- spheric absorption rate [1]. Accordingly, a high-performance antenna can be considered the most important part of wireless systems at such high frequencies. As a result of their high gain, wide bandwidth, and endfire radiation pattern, tapered slot antennas (TSAs) are a good candidate for high-data-rate wireless applications at 60 GHz [2]. In addition, TSAs are classified as traveling-wave planner antennas, a type especially suited for incorporation with other printed circuits. A linear tapered slot antenna (LTSA) fabricated on a low temperature co-fired ceramic (LTCC) substrate with high dielectric constant is proposed in [3]. However, it has low gain and degraded radiation pattern. Moreover, TSAs with numerous taper profiles have been presented, such as an exponentially tapered slot (Vi- valdi) antenna [4], [5], a constant-width slot antenna (CWSA) [6], and a broken linearly tapered slot antenna (BLTSA) [7]. Furthermore, TSAs with different inner taper profiles—Vivaldi, CWSA, BLTSA—and defined by Fermi–Dirac function were proposed by Sugawara et al. [8] and mainly used to improve the antenna radiation pattern at millimeter-wave (MMW) frequencies. Manuscript received August 01, 2014; accepted September 01, 2014. Date of publication September 09, 2014; date of current version January 30, 2015. The authors are with the Department of Electrical and Computer Engineering, Concordia University, Montréal, QC H3G 2W1, Canada (e-mail: is_mo@encs. concordia.ca; z_briqec@encs.concordia.ca; abdo@ece.concordia.ca). Color versions of one or more of the figures in this letter are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/LAWP.2014.2356137 Fig. 1. Antenna geometry. An approach to improve the radiation characteristics and miniaturize the antenna size by using an antipodal Fermi tapered slot antenna with rectangular corrugated edges is considered in [9]. The impact of rectangular and sine-shaped corrugation on Fermi TSA parameters is presented in [10]. Cheng et al. [11] proposed a modified antipodal Fermi antenna with a piecewise-linear slot that uses comb-shaped corrugations to improve the performance of the antenna at both lower and higher frequencies. In this letter, an antipodal Fermi tapered slot antenna (AFTSA) with sine-shaped corrugations is presented. To im- prove the radiation characteristics, impedance matching, and gain, two other related antennas were also constructed and evaluated. The first modified antenna was formed by cutting out a delta-shaped slot from the AFTSA, the second by loading an elliptical-shaped dielectric slab (LAFTSA) and cutting out a diamond-shaped slot from the antenna substrate. II. ANTENNA DESIGN Fig. 1 shows the geometry and the main design parameters of the antipodal Fermi tapered slot antenna with sine corrugations. The antenna was fabricated on an 8.7-mil-thick RO4003 sub- strate having relative permittivity of 3.55, covered on both sides by 17.5- m-thick copper. It is flared on either side of the sub- strate in opposite directions to configure the Fermi–Dirac taper profile according to the following equation: (1) where ( ) is an asymptotic value of the taper width, and the parameter ( ) is related to the gradient at the inflec- tion point ( ) of the Fermi–Dirac function. A balun pad (microstrip-to-slot transition) must be used to achieve the re- quired impedance matching. The antenna length was selected as , and the aperture width as , where is the free-space wavelength at 60 GHz. These values 1536-1225 © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.