Design of a Wideband High-Gain Metasurface Antenna Based on Characteristic Mode Theory

The Theory of Characteristic Modes (TCM) had its humble beginnings in the early 1970's. The beauty of TCM lies in its ability to fully characterize the radiation and scattering properties of an arbitrary object based only on the object's geometry and material properties. This ability provides valuable insights into an antenna's behavior independent of the feeding arrangement as well as providing information about how desirable radiation modes can be excited. This feature has led to its use to design integrated antennas in the High Frequency (HF) band for land vehicles, ships and aircraft. However, TCM had largely remained a specialist field until it was rediscovered for aiding the design of mobile handset antennas about a decade ago. In particular, TCM provides a powerful tool to understand and exploit excitation of the terminal chassis to enhance antenna performance. Another powerful feature of TCM is that multiple characteristic modes at a given frequency facilitate orthogonal radiation patterns, which provide effective Multiple-Input Multiple-Output (MIMO) antennas.

The Theory of Characteristic Modes (TCM) had its humble beginnings in the early 1970's. The beauty of TCM lies in its ability to fully characterize the radiation and scattering properties of an arbitrary object based only on the object's geometry and material properties. This ability provides valuable insights into an antenna's behavior independent of the feeding arrangement as well as providing information about how desirable radiation modes can be excited. This feature has led to its use to design integrated antennas in the High Frequency (HF) band for land vehicles, ships and aircraft. However, TCM had largely remained a specialist field until it was rediscovered for aiding the design of mobile handset antennas about a decade ago. In particular, TCM provides a powerful tool to understand and exploit excitation of the terminal chassis to enhance antenna performance. Another powerful feature of TCM is that multiple characteristic modes at a given frequency facilitate orthogonal radiation patterns, which provide effective Multiple-Input Multiple-Output (MIMO) antennas.

The Theory of Characteristic Modes (TCM) had its humble beginnings in the early 1970's. The beauty of TCM lies in its ability to fully characterize the radiation and scattering properties of an arbitrary object based only on the object's geometry and material properties. This ability provides valuable insights into an antenna's behavior independent of the feeding arrangement as well as providing information about how desirable radiation modes can be excited. This feature has led to its use to design integrated antennas in the High Frequency (HF) band for land vehicles, ships and aircraft. However, TCM had largely remained a specialist field until it was rediscovered for aiding the design of mobile handset antennas about a decade ago. In particular, TCM provides a powerful tool to understand and exploit excitation of the terminal chassis to enhance antenna performance. Another powerful feature of TCM is that multiple characteristic modes at a given frequency facilitate orthogonal radiation patterns, which provide effective Multiple-Input Multiple-Output (MIMO) antennas.

The theory of characteristic modes (TCM) is a versatile design and analysis tool that gives the unique possibility to determine the electromagnetic properties of a structure based only on its geometry and material properties. In antenna applications, this ability provides valuable insights into an antenna’s behavior independent of the feeding arrangement, as well as providing information about how desirable radiation modes can be excited. TCM had its humble beginnings in the early 1970s, largely through the pioneering works of Garbacz [1] and Harrington [2] , together with their co-workers.

The characteristic mode (CM) theory has been widely recognized as a powerful tool for radiation/scattering analysis and optimization designs. As a natural extension of PEC CM theory and dielectric material CM theory, we propose a novel CM formulation for the systematic analysis of dielectric coated conducting bodies. The newly developed CM formulation bases on the EFIE-PMCHWT equation. Numerical cases show the validity and accuracy of the proposed CM formulation in calculating characteristic currents and characteristic fields and predicting resonant frequencies.

The key to decreasing reradiation interference (RRI) of power transmission lines on adjacent radio stations is to clarify the RRI resonance mechanism. Aiming at the defects of existing RRI resonance analysis methods, including frequency limitation and lack of physical explanation, a RRI resonance analysis method based on characteristic mode (CM) theory is proposed in this paper. Firstly, based on the generalized eigenvalue equation, a set of characteristic currents with orthogonal relationship and their eigenvalues for power transmission lines are solved, and combined with Poynting’s theorem, the CM radiation characteristics are analyzed. Secondly, under specific external excitation, CM-related parameters are obtained through modal decomposition. Finally, the total energy radiated by power transmission lines is decomposed into the superposition of energy radiated by each CM, and the mechanism of RRI resonance is clarified from the perspective of CM. The simulation results show that compared with the IEEE guide and the generalized resonance theory, the method in this paper is effective and independent of observation points, which can provide a theoretical support for further research on the RRI suppression measures.

When analyzing object scattering, characteristic mode (CM) theory only focuses on the inherent properties of the target object and has nothing to do with any external factors. Different from traditional analytical eigenmode, characteristic mode method not only retains the advantages of clear theoretical concept of analytical eigenmode, but also combines the advantages of numerical method of moment (MoM) in dealing with irregular structures. Therefore the universality of the method is guaranteed. An aircraft example's analysis of radar cross section (RCS) using characteristic mode is given in this paper. The solution of characteristic equation can use implicit Arnoldi iterative algorithm. Characteristic mode theory provides theoretical support for the original antenna design so as to design an antenna with excellent performance.

We present a systematic method for designing dual-polarized, platform-mounted, high-frequency (HF) antennas for near vertical incidence skywave (NVIS) applications. To overcome the bandwidth (BW) and efficiency limitations of electrically small antennas, the characteristic mode (CM) theory is used to exploit the metallic platform as the main radiator. Low-profile coupling elements are mounted on different locations of the platform to excite two orthogonal, horizontally polarized CMs. This way, dual-polarized operation is achieved with a high isolation and sufficiently wide BW. In the design process, several key practical issues are taken into account and their impacts on the performance of the antenna are examined carefully. These include the type and design of the coupling elements, the presence and type of the earth, and the non-idealities and power handling capability in the impedance matching network components. The simulation results of both a full-scale and a 1:50 scaled model of the proposed structure are presented. The scaled-model prototype was fabricated and characterized in the presence of a ground plane emulating the properties of real earth at the scaled frequency of operation. The measurement results show a good agreement with the simulations, demonstrating the efficacy of the proposed approach in designing dual-polarized, platform-based HF antennas.

A novel design strategy for realizing a transmission-type polarization rotator of linearly polarized (LP) plane waves by exploiting the characteristic modes (CMs) theory is described. Design guidelines for the excitation of two current modes on a frequency selective surface (FSS), both exhibiting a circularly polarized (CP) radiated field, are provided to obtain the polarization rotation. The proposed converter exhibits remarkable performance also in the case of oblique incidence and a polarization-insensitive response thanks to the FSS unit cell compactness along with its fourfold rotational symmetry. Specifically, it provides a 3 dB cross-polar transmission percentage bandwidth up to 16.5% with a minimum insertion loss (IL) of 0.1 dB for a normally impinging plane wave whereas in case of an incidence angle of 60° the 3 dB cross-polar transmission percentage bandwidth turns out to be around 14% with a minimum IL of 0.7 dB. Measurements on a realized prototype are in good agreement with simulations, confirming the reliability of the proposed theoretical study.

A circularly polarized (CP) metasurface antenna is proposed in this paper. The metasurface is an array of subwavelength square patches. The characteristic modal of metasurface is analyzed by the theory of characteristic mode (TCM), and the desired characteristic mode is selected to form circular polarization radiation. Then, a proper feeding network is further empolyed to form CP radiation. Based on these concepts, an antenna with low profile is designed. The simulated results show that the impedance and axial-ratio(AR) bandwidths are 1.95 GHz and 1.05 GHz respectively, and their relative bandwidths are respectively 34.8% and 18.8%. Moreover, the antenna average gain is 6.25 dBi in the whole axial-ratio bandwidth.

In this letter, the Theory of Characteristic Modes (TCMs) is used to achieve pattern diversity in order to be used in multiple-input-multiple-output (MIMO) applications. It is shown that TCMs can orient the design procedure by providing an insight into the natural behavior of the analyzed radiating part of the structure. A metallic equilateral triangular-shaped plate is analyzed by TCMs, and its first seven characteristic modes are obtained. Among them, there are two sets of degenerative modes. All these modes are orthogonal. To achieve pattern diversity, it is essential to have two or more orthogonal radiation patterns with identical excitation frequency of the relevant ports. Therefore, the aforementioned sets can be used to acquire the pattern diversity. However, from obtained results, the set with the less practical implementation issues is selected to be excited. To perform the above-mentioned modal analysis, a specific method of moments (MoM) code has been developed and applied to identify different radiating modes. Two microstrip transmission lines were used as feeding parts so as to excite the suitable set of modes.

A miniaturized square microstrip patch antenna (MPA) is analyzed and designed using the theory of characteristic mode (TCM). The TCM is applied to investigate and adjust the current distribution of the lowest resonance mode that the square patch can support. Based on the current distribution of the concerned mode, the two opposite edges of the patch where the characteristic current mainly concentrates on are curved with quadratic function curves. Then stubs are periodically loaded on the curved-edges, and the current along the curved-edges occurs slight changes. At last, two apertures are etched on the patch, and more current trends to flow along the edges of the apertures. The above three approaches are examined through TCM, and all lead to reduction of resonance frequency of concerned mode. After optimizing the position of the probe-fed, a 60% miniaturization in the size of the square MPA is achieved. The TCM is expected to provide more effective guidance in antenna miniaturization design.

The theory of characteristic modes (TCM) for PEC bodies is showing great promise and application in the analysis, design, and placement of antennas. Its use for input impedance estimation, however, is still largely dependent on the idealized delta-gap model. Because TCM depends on all conductors, even feed structures, care must be taken for certain classes of antennas if estimating input impedance; probe-fed microstrip patch antennas (MSAs) are one example. In this paper, two different coaxial probe feed models are developed to estimate the input impedance of thin, arbitrarily shaped, air-dielectric MSAs using TCM. Their accuracy is compared with experimental results for a case study of an L-shaped MSA. Results show the importance of including all metal structures, including feeds, in TCM analyses.

A miniaturized microstrip patch antenna (MPA) design is analyzed using the theory of characteristic modes. The miniaturization is achieved by using an annular slot in the ground plane of the MPA. The theory of characteristic modes is applied to understand the resonant behavior of the antenna and to find the optimal location for the excitation of the antenna. Using this method, a 46% miniaturization in the size of MPA is achieved.

Metamaterial inspired concept is a very promising technique to miniaturize antennas suffering from their small electrical sizes while keeping a good radiation efficiency. In this paper, the theory of characteristic modes is used to perform a study of the powers and Q factors of metamaterial inspired antennas, such as the common 2D electric based monopole antenna with a meander line [1]. The aim of this work is to initiate to a new methodology to be used by antenna designers to address the problem of associating metamaterial inclusions to electrically small antennas in order to enhance their performances. It will be able to find the adequate inclusion in order to match an arbitrary shaped antenna in its electrically small regime and keep high overall efficiency. This will require the solving of the eigenvalue problem with further post-processing of the quantities provided by the theory of characteristic modes.