Optimal Dual-Antenna Design in a Small Terminal Multiantenna System

Abstract

This letter introduces a novel 2.6-GHz multiple-input-multiple-output (MIMO) antenna system for mobile terminals. The antenna structures consist of a broadband main antenna covering most of the LTE-A bands and a narrowband second antenna operating at the 2.6-GHz band. The main antenna is a traditional monopole-type capacitive coupling element (CCE) placed on the short edge of the terminal. The second antenna consists of two out-of-phase fed inductive coupling elements (ICEs) placed on the long edges of the chassis. The main purpose of the letter is to demonstrate that this kind of antenna system offers good performance in terms of electromagnetic (EM) isolation and envelope correlation between the antennas. This has been experimentally verified and is originated on the fact that both antennas excite effectively different orthogonal wavemodes, which is studied with the help of the theory of characteristic wavemodes.

Validating the Characteristic Modes Solvers

“…CM decomposition yields a set of realvalued currents which form an orthonormal basis with respect to their radiation patterns and the useful properties of the CMs render this technique appealing for antenna designers [5]- [7]. Consequently, CM decomposition has been the subject of implementation into commercial tools, such as FEKO [8], WIPL-D [9], and CST [10], and there also exist a plethora of academic tools, employed primarily for research related to the CM [11]- [14].…”

Capacitive coupling elements — Changing the way of designing antennas

“…The direct coupling, depending on implementation, can have very broadband characteristics, while the inductive coupler usually results in a narrowband performance. The capacitive and inductive or direct coupling approaches can also be combined within a single structure [5], [6]. In practice, realizing large slots on the chassis is not feasible in a typical mobile terminal, so the capacitive coupling element is usually the more attractive approach for a practical broadband antenna.…”

“…Furthermore, the antenna designer does not need to stick to the definition of CCE as a non-resonant antenna. A broader point of view can be used to create a hybrid antenna structure which operates like a CCE at low frequencies and like a self-resonant antenna at higher frequencies [6], [21].…”

Analyzing antenna effects on mobile chassis currents using theory of characteristic modes

“…The concept of non‐resonant inductive coupling elements and capacitive coupling element (CCE) slits for the excitation of the chassis modes was presented initially in . In, a 3‐port antenna system is designed.…”

“…The ports are used to excite the 3 chassis (120 × 60 ) modes at a frequency of 2.5 GHz. In, a 2‐port MIMO antenna system was presented. Here the chassis (115 × 60 ) mode was excited by using the chassis as a secondary antenna at 2.6 GHz.…”