Innovative DF Antenna Design, 16-R9818

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Principal Investigator
Keith A. Lysiak

Inclusive Dates:  04/04/08 – 01/10/09

Background - The purpose of this project is to investigate innovative designs for direction-finding antennas. The proposed plan capitalizes on a unique collaboration between SwRI and academia to update key SwRI engineering staff knowledge in the areas of antenna design, electromagnetic numerical modeling, and optimization while investigating new and innovative higher frequency antenna designs. SwRI had the opportunity to have a tenured university professor come to SwRI for a nine-month sabbatical to perform antenna research. Dr. Dave Kelley from Bucknell University was available from August 15, 2008, to May 19, 2009. Dr. Kelley is an outstanding engineer and educator.

Approach - Most communication systems simply require that the antenna receive a significant signal strength to obtain the information required. DF antenna systems, on the other hand, require not only a significant signal but also must have the ability to characterize the incident wave front of the signal of interest to determine the direction of arrival. This requires very stable and repeatable antenna responses. Because of this, DF antenna design requires a precision not required in most antenna applications. The objective of this project is to design innovative reflect arrays for direction-finding (DF) applications. Although reflect arrays have been designed for several specific applications including space, no mention of DF applications has been found in the referenced literature.

Accomplishments - Dr. Kelley developed several MATLAB algorithms to enable efficient optimization of reflect array responses. Many of these algorithms were modifications of algorithms that SwRI had developed for optimization and DF array design over the past decade. The key to these very efficient routines is a method developed by Dr. Kelley to create a large number of array response patterns while only running the main method of moments routine once. This is done through the use of embedded element pattern (EEP) data and the port-to-port mutual admittance matrix. This method is uniquely applicable to antenna systems altered only by impedance changes with no physical changes. Based on these optimization algorithms, several circular DF array designs were created that have single and double rings of reflectors around a single driven element. One of the more significant findings was that although typical reflect array designs used for communications purposes achieve bandwidths of nominally 10 percent, reflect arrays for DF applications can achieve better than a 2:1 frequency bandwidth. Although additional reflector elements do not extend the bandwidth, additional rings of different length reflectors can significantly increase the bandwidth.

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