Analysis of miniaturized MPA design using theory of characteristic modes

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.

This work introduces some preliminary results focused to point out that the theory of characteristic modes may help in the design of microstrip patch antennas, as it brings clear insight of the physical phenomena taking place in it, and presents no limitation over the height of the patch or the dielectric constant of the materials. Characteristic modes are defined as the real currents on the surface of a conducting body that depend on its shape and size, and are independent of the feed point. As characteristic modes form a close and orthogonal set of functions, they can be used to expand the total current. Another advantage of this method, is that for electrically small and intermediate size bodies, only a few modes are needed, and the problem can be dealt with only by considering two or three modes.

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.

In this paper, a frequency reconfigurable multiple-input-multiple-output (MIMO) slot antenna is presented. The proposed design is low profile and compact with wide tunability range, covering several well-known frequency bands from 1800 MHz to 2450 MHz. The frequency reconfigurability is achieved by loading the annular slot with varactor diodes. The antenna system is also analyzed for MIMO performance metrics. Moreover, the effect of circular slot antenna on the chassis modes is also investigated using the theory of characteristic modes (TCM). The physical principle behind frequency reconfigurability is also investigated using TCM analysis. An interesting finding is observed using varactor diodes for frequency reconfigurability, that is the reactive impedance loading does not alter the modal significance (MS) plots but only aid in the input impedance matching at different frequency bands.

In this work, a simple and efficient method to design uncorrelated antennas automatically is proposed based on the theory of characteristic mode, which set no limits on the shape of the antennas. Through theoretical derivation, we relate the correlation between antennas to the feeding vectors of the antennas, and provide guidelines for designing uncorrelated antennas. Beginning with the platform of a mobile handset and the excitation of the first antenna, the feeding of the other antennas, which can provide the least correlation with the predetermined ones, can be calculated numerically, until the maximum number of the antennas is achieved. Following the procedure, a multi-antenna system is designed step by step for the mobile handset at the center frequency of 2.6 GHz.

Bandwidth enhancement of low-profile slot antennas using theory of characteristic modes

To meet an implantable device for human disease detection, a conformal multiple-input–multiple-output (MIMO) antenna is investigated in this article. The layout and decoupling of the antenna are designed according to the inherent electromagnetic properties of the implanted device based on the theory of characteristic modes (TCM). Compared with traditional methods, the TCM provides a method and theory to design a conformal implantable antenna with MIMO properties. The designed antenna has the advantage of simple structure, low space occupation, and little multipath reflection. The newly designed structure adopts two planar helical radiators to achieve size miniaturization. Some I-type patches are located between two radiators and slotting structures on the ground plane to reduce coupling. The biocompatible flexible polyimide is used as a dielectric substrate, enabling the conformal property and compatibility with the human tissue. Measurements of the fabricated prototype have been finished in the minced pork and skin-mimicking gel. Results show very good agreement with the simulations, which validate the suitability of the proposed antenna for the implantable devices. To the best of our knowledge, this is the first time that the TCM has been applied to guiding the design of implantable MIMO antennas.

This paper presents a compact 5G multiple-input multiple-output (MIMO) microstrip antenna with isolation enhancement based on a slotted complementary split-ring resonator (SCSRR) and the theory of characteristic modes (TCMs). The metamaterial unit consists of three CSRR connected by extra slots. These added slots improve significantly the rejection response in terms of bandwidth and suppression. The dispersion diagram analysis is introduced to show the filtering characteristics of the band-gap structure before and after adding these additional slots. The TCM is employed to investigate the behavior of this 5G MIMO antenna before and after adding the slotted CSRR. The TCM is also applied to the MIMO antenna system to build up a precise methodology that can foresee whether the isolation can be upgraded further or not. The slotted CSRR is inserted meticulously in specific locations to block the coupling modes and almost does not affect the results of the noncoupling modes to improve the isolation remarkably. With this slotted CSRR, a 27-dB reduction in the mutual coupling between the two patch antennas is achieved. The whole design has been simulated utilizing the Microwave Studio CST ver. 18 simulator. The antenna being proposed is highly efficient and suitable for 5G wireless communication.

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.

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 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.

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.