Notes on Eigen Modal Analysis of Antennas

Authors: George Shaker, Nagula Sangary, and Safieddin Safavi-Naeini

Source: FERMAT, Volume 11, Article, Sep_Oct, 2015

Abstract: Modal analysis among the circuit and filter communities is widely spread. A close look at the design steps of many of the available modern filters reveals the utilization of modal techniques as a key design component [1]. Notably, modal analysis of antennas has long been known in the antenna community. Lo and Richards contributed significantly to the advancement of this theory in the late 1970s and early 1980s [2]. However, their approach was limited in its accuracy due to the utilization of some theoretical assumptions of the complex resonant frequencies of the antennas they studied. These assumptions imposed significant limitations on the antennas’ structures that could be analyzed, along with limitations on the achievable Q values. To date, modal analysis in antenna design has not evolved at the same rate it did in circuit/filter applications.

In this communication, the modal theory of antennas is revisited, believing that it brings invaluable information towards facilitating the design of multi-feed multi-band antennas. First, some subtle changes are proposed to enhance the applicability of this theory. Next, using some efficient computational techniques, the proposed formulations are shown to predict, to a very high accuracy, the input impedance of any antenna under study. This greatly simplifies the antenna problem and focuses design efforts on finding the appropriate complex resonance frequency to cover a required band. Finding the appropriate feed location is then a matter of extracting the corresponding impedance map for this antenna through simple field manipulations.

Index Terms: Antenna Design, Eigen Modes, LTE/MIMO Antenna, 4G smartphone

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Notes on Eigen Modal Analysis of Antennas