Antenna Systems & Technology - Fall 2016 - 7

FEATURE ARTICLE range of materials. Broadband performance is achieved in [5] by combining a small inductive coil with a planar dipole-type antenna, whereas [6] uses a complex design with multiple arrays of planar inverted-F antennas (PIFAs). Another method is making the antenna easily tunable to the specific dielectric by manually trimming in preset locations [3]. All of these approaches have used standard human-in-the-loop engineering methods. This article discusses a new method of designing RFID antennas over a wide range of substrates using automated synthesis. A New Design Approach In this new design approach, AntSyn was used to create new RFID antennas on a variety of substrates. AntSyn uses evolutionary algorithms (EAs), a programmatic method that leverages EM simulations to efficiently explore the design space and automatically locate high-performance design options. Antenna synthesis with AntSyn is proving to be highly effective at generating antenna structures with excellent performance and has already been used to create many successful fielded antennas, including several that have been used on spacecraft [7]. AntSyn allows the user to enter RF and form-factor specifications, such as bands, patterns, efficiency, geometry constraints, and more. It has a library of design templates and uses full-wave 3D simulation [8, 9] to obtain performance information on candidate designs. Advanced optimization algorithms are used to select and create antennas that are optimized to meet the user's requirements. A new capability has been added to AntSyn that enables a single antenna design to use a user-defined set of substrates Figure 2. Setting dielectric values in band control. during optimization. In AntSyn, the band control option enables the user to select many different performance criteria generally related to frequency bands, such as start and stop frequencies, pattern requirements, polarization, and cross-polarization levels. However, with the addition of this new feature, the user is now able to set capability, the dielectric constant as a parameter for each band, if desired (Figure 2). This flexibility allows the user to essentially set up dielectric test cases for the antenna design. To do so, all criteria in each band is kept the same (impedance match, pattern), except for the dielectric. Each band is then given a different value for dielectric constant and loss tangent. AntSyn then directly optimizes performance for the antenna across the range of dielectrics. A new type of antenna has been created to take advantage of this optimization capability specifically for RFID antennas. Based on a very generic type of antenna, the "planar-XYmesh" type shown in Figure 3, the new antenna type has been used for small, integrated antennas (see [10] for some examples). This type is typically a PIFA-style antenna with a ground layer. For this effort, a new antenna type was added that is a singlelayer design, but still on a dielectric substrate. In this antenna, the substrate is now used to simulate the surface on which the RFID antenna will be installed, instead of being a part of the antenna itself. When coupled with the band-dielectric control described above, it enables the optimization of RFID antennas across a range of installation environments. Figure 3. Example of original planar XYmesh antenna with dielectric on ground plane. Article continued on page 8 www.AntennasOnline.com Fall 2016 Antenna Systems & Technology 7 http://www.AntennasOnline.com

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