| 1. |
- Li, Hui, et al.
(author)
-
Design of Orthogonal MIMO Handset antennas based on characteristic mode manipulation at frequency bands below 1 GHz
- 2014
-
In: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 62:5, s. 2756-2766
-
Journal article (peer-reviewed)abstract
- Multi-antenna design in compact mobile handsets at frequency bands below 1 GHz is very challenging, since severe mutual coupling is commonly induced by simultaneous excitation of the chassis’ fundamental dipole mode by more than one antenna element. To address this problem, a novel multi-antenna design approach is proposed herein to obtain efficient and uncorrelated antennas. By manipulating the chassis structure, more than one characteristic mode is enabled to resonate at frequencies below 1 GHz. With proper excitations for different characteristic modes, which are orthogonal to each other, well matched multi-antennas with low coupling and correlation are achieved. A chassis loaded with two T-shaped metal strips above its edges is taken as an example modification to illustrate the effectiveness of the proposed design approach at 900 MHz. This modification creates a new characteristic mode which resonates near 900 MHz.. Afterward, two antenna feeds were designed to efficiently excite the chassis’ fundamental dipole mode and the T-strip mode with very low correlation. The T-strip antenna covers LTE Band 8 (880-960 MHz), and the dipole mode antenna covers both LTE Band 5 (824-894 MHz) and LTE Band 8. The proposed dual-antenna design was found to outperform a reference design significantly, both with and without user interactions (i.e., one-hand and two-hand data grips). Practical aspects of mobile handset antennas are also investigated. The prototype was also fabricated and measured, and the measured results show reasonable agreements with the simulated results.
|
|
| 2. |
- Li, Hui, et al.
(author)
-
Generating multiple characteristic modes below 1 GHz in small terminals for MIMO antenna design
- 2013
-
In: IEEE International Symposium on Antennas and Propagation, 2013. - 1947-1491 .- 1522-3965. - 9781467353175 ; , s. 180-181
-
Conference paper (peer-reviewed)abstract
- Designing multiple antennas in small terminals at frequency bands below 1 GHz is challenging due to severe mutual coupling among antenna elements. The severe coupling is often the result of simultaneous excitation of the fundamental characteristic mode of the terminal chassis by more than one antenna element. In this work, we propose to solve the coupling problem by manipulating the chassis structure to allow more than one characteristic mode to resonate at frequencies below 1 GHz. To demonstrate our design concept and its practicality, we show the opportunistic use of the metallic bezel popular in smartphone design for obtaining two characteristic modes that can be efficiently excited by antenna elements at 0.81 GHz. Due to the inherent orthogonality of the modes, proper excitation of these modes by two antenna elements will result in orthogonal radiation patterns and high isolation between the antenna ports. Therefore, the proposed approach enables the effective use of the chassis to achieve MIMO antennas with good performance.
|
|
| 3. |
|
|
| 4. |
- Miers, Zachary, et al.
(author)
-
Antenna design using characteristic modes for arbitrary materials
- 2016
-
In: 2016 IEEE International Symposium on Antennas and Propagation (APSURSI). - 9781509028863
-
Conference paper (peer-reviewed)abstract
- Characteristic mode analysis has traditionally been constrained to problems which utilize only perfect electric conductors (PEC). Through forced symmetry of a method of moments surface integral equation and newly proposed post-processing, characteristic modes can be solved for any material in a computationally efficient manner. As an example, the characteristic modes are solved for a mobile terminal consisting of both PEC and dielectric materials.
|
|
| 5. |
|
|
| 6. |
- Miers, Zachary, et al.
(author)
-
Computational analysis and verifications of characteristic modes in real materials
- 2016
-
In: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 64:7 (Special Issue), s. 2595-2607
-
Journal article (peer-reviewed)abstract
- Despite its long history, the Theory of Characteristic Modes has only been utilized in antenna design for perfect electric conductors. This is due to computational problems associated with dielectrics and magnetic materials. In particular, the symmetric form of the PMCHWT surface formulation for the Method of Moments (MoM) solves for both external (real) and internal (non-real) resonances of a structure. The external resonances are the characteristic modes, whereas the internal resonances are not. This article proposes a new post-processing method capable of providing unique and real characteristic modes in all physical mediums, including lossy magnetic and dielectric materials. The method removes the internal resonances of a structure by defining a minimum radiated power, which is found through utilizing the physical bounds of the structure. The characteristic modes found using the proposed method are verified through the use of a MoM volume formulation, time domain antenna simulations, and experiments involving multiple antenna prototypes.
|
|
| 7. |
- Miers, Zachary, et al.
(author)
-
Design of bandwidth enhanced and multiband MIMO antennas using characteristic modes
- 2013
-
In: IEEE Antennas and Wireless Propagation Letters. - 1548-5757. ; 12, s. 1696-1699
-
Journal article (peer-reviewed)abstract
- Recent work has shown that, with the help of the Theory of Characteristic Modes (TCM), minor modifications of the terminal chassis can facilitate the design of orthogonal MIMO antennas with viable bandwidth at frequencies below 1 GHz. Herein, a new framework is proposed to further exploit TCM to enhance the performance of the orthogonal MIMO antennas. By correlating the characteristic currents and near fields of modes with high modal significance in a given frequency band, a single feed may be designed to excite multiple modes, leading to enlarged bandwidth. Similarly, the correlation of characteristic currents and near fields across different bands provides candidate modes that can be excited for multiband operation using a single feed. Moreover, the impedance matching of these modes can be improved by additional structural manipulation. As proof of concept, a dual-band (818-896MHz, 1841-2067MHz), dual-antenna prototype was designed on a 130 mm by 66 mm chassis for LTE operation. Full-wave simulation results were experimentally verified with a fabricated prototype.
|
|
| 8. |
- Miers, Zachary, et al.
(author)
-
Design of bezel antennas for multiband MIMO terminals using characteristic modes
- 2014
-
In: European Conference on Antennas and Propagation (EuCAP), 2014. - 2164-3342. ; , s. 2556-2560
-
Conference paper (peer-reviewed)abstract
- Designing decorrelated MIMO antennas in small mobile terminals at frequencies below 1 GHz is challenging since more than one antenna tend to excite the single resonant mode available to a typical chassis structure. This challenge increases even further when multiple frequency bands are required from each antenna. Recently, a design framework to obtain efficient and decorrelated MIMO antennas based on the Theory of Characteristic Modes was proposed. By slightly modifying the chassis, multiple orthogonal resonant modes may be created and excited to facilitate low correlation at frequencies below 1 GHz. In addition, multiband operation per antenna can be achieved by correlating the characteristic currents of different modes across different frequency bands. In this work, we apply the proposed framework to make opportunistic use of the bezel structure popular in mobile terminal designs to achieve efficient and uncorrelated multiband MIMO antennas.
|
|
| 9. |
- Miers, Zachary, et al.
(author)
-
Design of MIMO terminal antennas with user proximity using characteristic modes
- 2017
-
In: 2017 11th European Conference on Antennas and Propagation, EUCAP 2017. - 9788890701870 ; , s. 2649-2651
-
Conference paper (peer-reviewed)abstract
- Although the classical Theory of Characteristic Modes allows an arbitrary structure to be analyzed prior to the implementation of physical feeds, structures containing dielectrics have so far received very little attention. Recently, a mesh perturbation method is proposed to remove internal resonances from the characteristic mode (CM) solution for lossy dielectrics obtained using the computationally efficient surface integral equation. Herein this method was applied to extract the CMs of a lossy structure consisting of a terminal chassis held in a user hand. These modes were then individually analyzed and a subset was chosen to design a MIMO antenna with not only very low correlation, but also low hand-induced losses.
|
|
| 10. |
- Miers, Zachary, et al.
(author)
-
Design of multi-antenna feeding for MIMO terminals based on characteristic modes
- 2013
-
In: IEEE International Symposium on Antennas and Propagation, 2013. - 1522-3965 .- 1947-1491. - 9781467353175 ; , s. 182-183
-
Conference paper (peer-reviewed)abstract
- Conventional antennas in single-antenna terminals that resonate at frequencies lower than 1 GHz usually rely on the chassis as the main radiator. To effectively exploit chassis excitation for MIMO terminals, each of the multiple antennas is required to excite one distinct chassis mode. However, in today's terminals, there is typically only one chassis mode that can radiate efficiently at frequencies below 1 GHz. Fortunately, it has been shown that minor modifications in the chassis structure can cause more than one mode to resonate at these frequencies. Nevertheless, proper antenna feeding methods are needed to practically tap into these modes. In this paper, we propose a general technique to feed orthogonal chassis modes of a given conducting structure using the theory of characteristic modes. By separating a radiating structure into individual modal currents, the near field radiating properties are exploited for capacitive or inductive feeding without significant coupling to other orthogonal modes of radiation. As a proof of concept, we apply the technique to feed a modified terminal chassis that has two significant characteristic modes at 0.89 GHz.
|
|
