A compact rectangular monopole with an equal-width ground plane is presented. This novel structural configuration could significantly improve its radiation performance and decrease its size. The feeding structure composed of a trident-shaped strip and a tapered impedance transformer is presented and discussed. Its impedance bandwidth, defined by measured VSWR less than 2, is from 2.75 to 16.2 GHz with a ratio of about 5.9:1. Both numerical and experimental results show that the proposed monopole antenna has stably omni-directional H-plane radiation patterns with low cross-polarization level within its impedance bandwidth. This novel monopole antenna has ultrawide impedance bandwidth, very compact size (30 mm*8 mm), low fabrication lost, and omni-directional H-plane radiation patterns, which are suitable for various broadband applications.

Out-of-band interference by antenna coupling is frequently encountered and difficult to compensate. In this paper, it is studied for the first time using characteristic mode analysis (CMA). Mutual coupling between two antennas is separated into several fundamental modes, and the contribution of each mode is evaluated through modal mutual admittance (MMA). Some higher order modes, which contribute little to the in-band radiation but much to the out-of-band coupling, are discriminated and controlled by means of inductive loadings. The placement of loadings is suggested by the distribution of eigencurrents and optimum values are obtained by evaluating the MMA. Numerical and experimental results are presented for verification.

An L-sleeve L-monopole (LSLM) antenna fitting a shark-fin module is proposed for vehicular long term evolution (LTE) communication. Starting with classical sleeve monopole antennas, a low-profile evolution is introduced to explain the working principle of the LSLM. The influence of the ground plane, placement position, and bent of the LSLM is analyzed to fit different shark-fin modules. Designed prototypes (the LSLM and bended LSLM) cover the frequency range of 698-2700 MHz (VSWR < 3), which would serve major LTE standards. One tab monopole antenna covering the frequency range of 5-6 GHz can be integrated in the shark-fin module and provide services for wireless local area network and car-to-car communications. Low mutual coupling (lower than -23 dB) between the two antennas is achieved in the frequency range of 698-6000 MHz without any additional filters, and the design method is presented for better understanding the underlying physics. The proposed antenna is fabricated on an affordable printed circuit board, which is useful for vehicular applications.

In this article, the characteristic mode analysis (CMA) of general metallic-dielectric structures is performed using the volume-surface integral equation (VSIE). The whole-structure and substructure formulations for the CMA are presented and discussed. It is proven that only the substructure operator is symmetrical and therefore fulfills CMA's theoretic requirements. Such a symmetrical operator ensures that the computed eigencurrents are orthogonal and the eigenvalues are real numbers. Numerical analysis verifies that the substructure formulation yields more accurate results than the whole-structure one. A smartphone chassis on an FR-4 substrate and a split-ring resonator (SRR) on a Teflon substrate are analyzed using the presented method. The influence of the mesh size is discussed and it is shown that the volume mesh density increases at a rate similar to the surface mesh. In short, the volume-surface integral formulation with a substructure treatment is versatile, stable, and reasonably efficient for the CMA of thin metallicdielectric structures with planar or curved shapes.

The theory of inner resonant modes (IRMs) is very useful for the analysis and design of dielectric resonator antennas (DRAs), but it suffers from several limitations including canonical DRA shapes, high permittivity substrate, and large errors. Characteristic modes (CMs) contain similar physical insights but without the limitations owing to its full-wave nature. In this paper, a new approach is proposed for the codesign of DRAs and feeding structures using CMs. The volume-surface formulation combining substructure treatment is adopted to calculate CMs of DRAs. To detailedly demonstrate the proposed method, electric and magnetic feeding structures are utilized to excite a cubic DRA as examples. Compared with the results obtained by an isolated design of DRAs and feeding structures, characteristic mode analysis (CMA) of the whole structure reveals several new modes, in which the lower order modes correspond to much lower resonant frequencies. Proper modifications of the feeding structures can effectively excite these modes and result in dual- and triple-band operation. Several prototypes were fabricated and measured for verification. For a cubic DRA with a side length of 25.4 mm, it achieves a triple-band operation at 1.6, 3.1, and 4.6 GHz. Therefore, this method is ideal for the codesign of arbitrary DRAs with feeding structures.