The Theory of Characteristic Modes Revisited: A Contribution to the Design of Antennas for Modern Applications

Abstract

The objective of this paper is to summarize the work that has been developed by the authors for the last several years, in order to demonstrate that the Theory of Characteristic Modes can be used to perform a systematic design of different types of antennas. Characteristic modes are real current modes that can be computed numerically for conducting bodies of arbitrary shape. Since characteristic modes form a set of orthogonal functions, they can be used to expand the total current on the surface of the body. However, this paper shows that what makes characteristic modes really attractive for antenna design is the physical insight they bring into the radiating phenomena taking place in the antenna. The resonance frequency of modes, as well as their radiating behavior, can be determined from the information provided by the eigenvalues associated with the characteristic modes. Moreover, by studying the current distribution of modes, an optimum feeding arrangement can be found in order to obtain the desired radiating behavior.

Analysis and Design of a Metamaterial Lens Antenna Using the Theory of Characteristic Modes

“…As exposed in [10,11] and [13], the characteristic modes (J n ) are real current modes that are extracted at every frequency from the generalized impedance matrix of the antenna. These characteristic modes form a set of orthogonal functions that can be used to expand the total current in the surface of the antenna, as described in the following equations:…”

“…Observe that modes are capacitive for α n > 180 ∘ , inductive for α n < 180 ∘ , and resonate for α n = 180 ∘ [13].…”

“…As can be seen, currents of mode 1 form a loop inside and outside the total structure. modes 2 and 3 are a pair of degenerated modes [13], representing the modal current of the dominant modes, which generate a broadside radiation pattern. These broadside modes are the desired modes for the antenna design.…”

“…This theory was initially formulated by Garbacz and Turpin [10] and then refined by Harrington and Mautz [11,12]. The TCM was shown to be really helpful for the analysis and design of several antenna structures [13]. The popularity of this theory relies on the fact that it provides a very clear understanding of the radiating behavior of metallic and dielectric bodies, which ease the design process.…”

“…In addition to the first applications of the TCM reviewed in [13], this theory has been recently used to analyze the bandwidth of a 2 × 2 bowtie array with a metasurface [14], design electrically small unmanned aerial vehicle (UAV) antennas [15], design and analyze slotted planar structures [16], or study some canonical structures such as spheres or cylinders [17]. Moreover, a single-layer metal lens formed by a central circular metallic ring surrounded by a set of eight metallic rings was analyzed using the TCM in [18], a wideband low-profile metasurface antenna was modeled and optimized using characteristic modes in [19], and a low-profile lens using metallic cylinders was investigated in [20] using the TCM.…”