A Generalized Modal Analysis Method for Antenna Design

Modal analysis of antennas has long been known in the antenna community. The work in [1], [2] was a corner stone to the advancement of this theory in the late 1970s and early 1980s. However, the theory was only applied to simple planar microstrip-based structures. Even for the most basic antenna forms, the technique was limited in its accuracy due to the utilization of admittance boundary conditions at the structure physical edges. In this work, the modal theory of antennas is re-visited, believing that it brings invaluable information towards facilitating the general antenna design problem. This is particularly true when seeking multi-slot/multi-feed/multi-band antenna designs. First, some modifications are introduced to enhance the applicability of the modal theory. Next, using some efficient computational methods, the proposed formulation is shown to predict, with a very high accuracy, the input impedance of any antenna under study. This greatly simplifies the antenna design problem and focuses the 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. No extra expensive electromagnetic simulations are needed. A simple dual-feed dual-band example is used to illustrate the potentials of the proposed formulations.