17 results on '"Zachary Miers"'
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2. Computational Analysis and Verifications of Characteristic Modes in Real Materials
- Author
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Zachary Miers and Buon Kiong Lau
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Magnetic domain ,dielectric resonant antenna ,Antenna design ,quality factor ,02 engineering and technology ,Dielectric ,Electrical Engineering, Electronic Engineering, Information Engineering ,Effective radiated power ,Method of moments (statistics) ,Topology ,01 natural sciences ,MIMO systems ,0103 physical sciences ,0202 electrical engineering, electronic engineering, information engineering ,Time domain ,Electrical and Electronic Engineering ,Electrical impedance ,010302 applied physics ,Physics ,business.industry ,Electrical engineering ,020206 networking & telecommunications ,Integral equation ,characteristic modes ,Antenna (radio) ,business - Abstract
Despite its long history, the theory of characteristic modes (TCMs) has only been utilized in antenna design for perfect electric conductors (PECs). This is due to computational problems associated with dielectric and magnetic materials. In particular, the symmetric form of the Poggio–Miller–Chan–Harrington–Wu–Tsai (PMCHWT) surface formulation for the method of moments (MoM) solves for both external (real) and internal (nonreal) resonances of a structure. The external resonances are the characteristic modes (CMs), whereas the internal resonances are not. This paper proposes a new postprocessing method capable of providing unique and real CMs 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 CMs found using the proposed method are verified through the use of an MoM volume formulation, time domain antenna simulations, and experiments involving multiple antenna prototypes.
- Published
- 2016
3. Restoring characteristic eigenvalues as reactive powers for simple and complex media in surface integral formulations
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Zachary Miers and Buon Kiong Lau
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Antenna analysis ,020208 electrical & electronic engineering ,Surface integral ,Mathematical analysis ,Communication Systems ,Method of moments ,Poynting’s theorem ,020206 networking & telecommunications ,02 engineering and technology ,AC power ,Method of moments (statistics) ,Interpretation (model theory) ,Modal ,Characteristic modes ,Poynting's theorem ,Simple (abstract algebra) ,0202 electrical engineering, electronic engineering, information engineering ,Eigenvalues and eigenvectors ,Mathematics - Abstract
The Theory of Characteristic Modes (TCM) has recently been shown to be beneficial in solving a wide variety of complex electromagnetic problems. However, there are still open issues in using TCM to analyze objects which consist of simple or complex media. Either a volume integral equation (VIE) or a surface integral equation (SIE) is required to solve for the characteristic modes of these objects. Herein, we overview the important issue that the characteristic eigenvalues obtained from SIE formulations are not related to the modal reactive power, unlike the classical TCM definition. A recently proposed solution that restores the modal reactive power interpretation of characteristic eigenvalues is described. A numerical example is provided to demonstrate the differences between the SIE eigenvalues and the restored eigenvalues.
- Published
- 2017
4. Design of MIMO terminal antennas with user proximity using characteristic modes
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Zachary Miers and Buon Kiong Lau
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Engineering ,Chassis ,business.industry ,020208 electrical & electronic engineering ,MIMO ,Structure (category theory) ,020206 networking & telecommunications ,02 engineering and technology ,Dielectric ,Lossy compression ,user interaction ,Topology ,MIMO system ,Mode (computer interface) ,Terminal (electronics) ,characteristic modes ,Telecommunications ,0202 electrical engineering, electronic engineering, information engineering ,Electronic engineering ,Low correlation ,business ,Terminal antennas ,Computer Science::Information Theory - 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.
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- 2017
5. Design of Orthogonal MIMO Handset Antennas Based on Characteristic Mode Manipulation at Frequency Bands Below 1 GHz
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Zachary Miers, Buon Kiong Lau, and Hui Li
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Physics ,Directional antenna ,business.industry ,Acoustics ,Antenna measurement ,Electrical engineering ,Slot antenna ,Electrical Engineering, Electronic Engineering, Information Engineering ,law.invention ,Biconical antenna ,law ,Dipole antenna ,Electrical and Electronic Engineering ,Antenna (radio) ,Omnidirectional antenna ,business ,Monopole antenna - 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 longer 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.
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- 2014
6. Effects of dielectrics and internal resonances on modal analysis of terminal chassis
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Zachary Miers and Buon Kiong Lau
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method of moments ,Materials science ,Modal analysis ,020206 networking & telecommunications ,02 engineering and technology ,Dielectric ,Electrical Engineering, Electronic Engineering, Information Engineering ,dielectric material ,Method of moments (statistics) ,Impedance parameters ,Dielectric spectroscopy ,Computational physics ,0202 electrical engineering, electronic engineering, information engineering ,Electronic engineering ,Symmetric matrix ,Theory of Characteristic Modes ,terminal antennas ,Electrical conductor ,Electrical impedance - Abstract
The symmetric PMCHWT method of moments (MoM) impedance matrix allows for the characteristic modes (CMs) of a structure containing dielectric to be found. Recently, this impedance matrix was proven to provide non-real solutions which can be attributed to the MoM internal resonance problem. These internal resonances can be removed through different CM post-processing techniques. However, these studies focus on dielectric structures, whereas the majority of antennas utilize electric conductors as the radiators. As such, dielectrics are often neglected to simplify the CM analysis and hence the problem of internal resonance is overlooked. This work explores the extent of the internal resonance problem in mixed conductor-dielectric structures. The results reveal that the problem is severe even when the structures only contain small amounts of dielectric materials. Moreover, the significant impact of dielectrics on CMs reveals that dielectrics should be included in CM analysis to ensure high accuracy.
- Published
- 2016
7. Post-processing removal of non-real characteristic modes via basis function perturbation
- Author
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Buon Kiong Lau and Zachary Miers
- Subjects
Lossless compression ,020208 electrical & electronic engineering ,Mathematical analysis ,020206 networking & telecommunications ,Basis function ,Geometry ,02 engineering and technology ,Dielectric ,Lossy compression ,Electrical Engineering, Electronic Engineering, Information Engineering ,Impedance parameters ,Matrix decomposition ,Characteristic modes ,dielectric resonator antennas ,0202 electrical engineering, electronic engineering, information engineering ,Symmetric matrix ,Electrical impedance ,Mathematics ,antenna design - Abstract
For more than 30 years since it was first proposed by Harrington et al., the Theory of Characteristic Mode (TCM) has only been applied to perfect electric conductors (PEC), and more recently lossless dielectric materials. One key challenge in computing the characteristic modes (CMs) of non-PEC materials using the PMCHWT surface integral equation is the presence of internal resonances in the solution space, due to the required forcing of symmetry on the impedance matrix. In lossless dielectrics, it was shown that these non-real CMs can be removed in post-processing through far-field power analysis. However, this method breaks down in lossy materials as it relies on the assumption of no radiation losses. This paper proposes the use of basis function perturbation to isolate the non-real CMs from the real CMs when CM analysis is applied to lossy materials.
- Published
- 2016
8. Antenna design using characteristic modes for arbitrary materials
- Author
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Zachary Miers and Buon Kiong Lau
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Mathematical analysis ,Physics::Optics ,020206 networking & telecommunications ,02 engineering and technology ,Dielectric ,Method of moments (statistics) ,Electrical Engineering, Electronic Engineering, Information Engineering ,Integral equation ,Symmetry (physics) ,Computational electromagnetics ,Terminal (electronics) ,Characteristic mode analysis ,0202 electrical engineering, electronic engineering, information engineering ,Theory of Characteristic Modes ,Electrical impedance ,Mathematics ,antenna design - 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.
- Published
- 2016
9. Tracking of characteristic modes through far-field pattern correlation
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Buon Kiong Lau and Zachary Miers
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Engineering ,business.industry ,MIMO ,Degenerate energy levels ,Mode (statistics) ,Near and far field ,Dielectric ,Electrical Engineering, Electronic Engineering, Information Engineering ,Tracking (particle physics) ,Topology ,Information engineering ,Electronic engineering ,business ,Electrical conductor - Abstract
Recent developments in characteristic mode (CM) analysis enable a more systematic approach to designing multi-antennas for mobile terminals. However, some of the advantages of developing antennas through CMs are based on accurate mode tracking over frequency. Existing tracking methods are primarily based on the tracking of eigencurrents over frequency, by which mode swapping and degenerate modes can occur. To solve these problems, a completely different method of tracking CM by means of far-field pattern correlation was recently developed and shown to work well for perfect electric conductors (PECs). This paper reveals that the same method can also substantially reduce tracking errors for structures with both PEC and dielectric materials, relative to state-of-the-art methods.
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- 2015
10. Wide band characteristic mode tracking utilizing far-field patterns
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Zachary Miers and Buon Kiong Lau
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Reconfigurable antenna ,Directional antenna ,Antenna measurement ,Near and far field ,Electrical Engineering, Electronic Engineering, Information Engineering ,Tracking (particle physics) ,Topology ,law.invention ,law ,Electronic engineering ,Electrical and Electronic Engineering ,Wideband ,Antenna (radio) ,Eigenvalues and eigenvectors ,Mathematics - Abstract
The Theory of Characteristic Modes provides a convenient tool for designing multi-antennas for multiple-input multiple-output applications, as it enables orthogonal radiation patterns to be excited in a given antenna structure. Moreover, the frequency behavior of the modes reveals interesting wideband properties of the structure. However, the tracking of characteristic modes over frequency remains a challenge, especially when differences between modes are limited to high currents in small regions of the structure. The common approach of tracking characteristic modes is through correlating the modal currents over frequency, this leads to multiple eigenvalues being mapped to the same eigencurrent. In this letter, we propose a new approach to track characteristic modes by means of cross correlating far-field patterns, which effectively eliminates the mode mapping ambiguity.
- Published
- 2015
11. On Characteristic Eigenvalues of Complex Media in Surface Integral Formulations
- Author
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Buon Kiong Lau and Zachary Miers
- Subjects
010302 applied physics ,Other Electrical Engineering, Electronic Engineering, Information Engineering ,Electromagnetics ,Mathematical analysis ,Surface integral ,020206 networking & telecommunications ,02 engineering and technology ,Mathematics::Spectral Theory ,Method of moments (statistics) ,AC power ,01 natural sciences ,Modal ,0103 physical sciences ,Poynting vector ,0202 electrical engineering, electronic engineering, information engineering ,Electrical and Electronic Engineering ,Electrical impedance ,Eigenvalues and eigenvectors ,Mathematics - Abstract
Although surface integral equations (SIEs) have been extensively used in solving electromagnetic problems of penetrable objects, there are still open issues relating to their application to the Theory of Characteristic Modes. This work demonstrates that when an SIE is used to solve for the characteristic modes (CMs) of a dielectric or magnetic object, the resulting eigenvalues are unrelated to the reactive power of the object, unlike the eigenvalues of perfect electric conductors. However, it is proposed that the classical eigenvalues, which provide useful physical insights, can be extracted from the SIE CM solution using Poynting’s theorem. Large discrepancies between the SIE CM eigenvalues and the proposed eigenvalues, as well as eigenvalue-derived characteristic quantities, are highlighted using a numerical example. The modal resonances as predicted by the proposed eigenvalues closely match those obtained for natural resonance modes.
- Published
- 2017
12. Design of bezel antennas for multiband MIMO terminals using Characteristic Modes
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Hui Li, Zachary Miers, and Buon Kiong Lau
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3G MIMO ,Engineering ,Reconfigurable antenna ,Directional antenna ,business.industry ,mutual coupling ,Antenna measurement ,Smart antenna ,mobile antenna ,Electrical Engineering, Electronic Engineering, Information Engineering ,Antenna array ,Multi-user MIMO ,MIMO systems ,law.invention ,Folded inverted conformal antenna ,law ,characteristic modes ,Electronic engineering ,Antenna (radio) ,business ,antenna design ,Computer Science::Information Theory - 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.
- Published
- 2014
13. Design of multimode multiband antennas for MIMO terminals using characteristic mode analysis
- Author
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Zachary Miers and Buon Kiong Lau
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3G MIMO ,Engineering ,Multi-mode optical fiber ,Chassis ,Directional antenna ,business.industry ,Frequency band ,MIMO ,Bandwidth (signal processing) ,Electrical engineering ,Electrical Engineering, Electronic Engineering, Information Engineering ,Characteristic mode analysis ,Hardware_GENERAL ,Electronic engineering ,business ,Computer Science::Information Theory - Abstract
Characteristic mode analysis provides unparalleled insights into designing high performance multiple-input multiple-output (MIMO) terminal antennas at frequencies where the antenna elements are constrained to be electrically small. Conventionally, an electrically small single-antenna utilizes the fundamental characteristic mode of the terminal chassis to obtain sufficient bandwidth while maintaining high radiation efficiency. However, modern MIMO terminals require two or more antennas per frequency band, and they tend to excite the same fundamental chassis mode, resulting in severe coupling and correlation, and poor overall system performance. Recently, characteristic mode analysis of the chassis is proposed to design highly efficient multimode multiband MIMO antennas with significant bandwidth using electrically small feed elements. Two distinct and excitable characteristic modes were created at frequencies above and below 1 GHz, for a typical smartphone’s form factor. This paper provides an overview of the method and highlights its versatility for practical implementation in standard plastic cased smartphones as well as in the popular metal-bezeled smartphones, with only minor modifications to the chassis. (Less)
- Published
- 2014
14. A flexible 100-antenna testbed for Massive MIMO
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Zachary Miers, Joao Vieira, I.C. Wong, Steffen Malkowsky, Liang Liu, Karl F. Nieman, Nikhil Kundargi, Viktor Öwall, Ove Edfors, and Fredrik Tufvesson
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3G MIMO ,Orthogonal frequency-division multiplexing ,Computer science ,Real-time computing ,MIMO ,Throughput ,Data_CODINGANDINFORMATIONTHEORY ,Electrical Engineering, Electronic Engineering, Information Engineering ,Precoding ,testbed ,Base station ,Telecommunications link ,large array ,system description ,business.industry ,Testbed ,ComputerSystemsOrganization_COMPUTER-COMMUNICATIONNETWORKS ,Software-defined radio ,MIMO-OFDM ,Multi-user MIMO ,Spatial multiplexing ,Baseband ,prototype ,business ,Massive MIMO ,Decoding methods ,Computer hardware ,5G ,Communication channel - Abstract
Massive multiple-input multiple-output (MIMO) is one of the main candidates to be included in the fifth generation (5G) cellular systems. For further system development it is desirable to have real-time testbeds showing possibilities and limitations of the technology. In this paper we describe the Lund University Massive MIMO testbed – LuMaMi. It is a flexible testbed where the base station operates with up to 100 coherent radio-frequency transceiver chains based on software radio technology. Orthogonal Frequency Division Multiplex (OFDM) based signaling is used for each of the 10 simultaneous users served in the 20 MHz bandwidth. Real time MIMO precoding and decoding is distributed across 50 Xilinx Kintex-7 FPGAs with PCI-Express interconnects. The unique features of this system are: (i) high throughput processing of 384 Gbps of real time baseband data in both the transmit and receive directions, (ii) low-latency architecture with channel estimate to precoder turnaround of less than 500 micro seconds, and (iii) a flexible extension up to 128 antennas. We detail the design goals of the testbed, discuss the signaling and system architecture, and show initial measured results for a uplink Massive MIMO over-the-air transmission from four single-antenna UEs to 100 BS antennas.
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- 2014
15. Generating multiple characteristic modes below 1 GHz in small terminals for MIMO antenna design
- Author
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Hui Li, Zachary Miers, and Buon Kiong Lau
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Reconfigurable antenna ,Engineering ,Directional antenna ,business.industry ,Antenna measurement ,Astrophysics::Instrumentation and Methods for Astrophysics ,Antenna factor ,Electrical Engineering, Electronic Engineering, Information Engineering ,Antenna efficiency ,law.invention ,law ,Electronic engineering ,Dipole antenna ,Antenna (radio) ,business ,Omnidirectional antenna ,Computer Science::Information Theory - 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.
- Published
- 2013
16. Design of bandwidth enhanced and multiband MIMO antennas using characteristic modes
- Author
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Buon Kiong Lau, Zachary Miers, and Hui Li
- Subjects
3G MIMO ,Engineering ,Reconfigurable antenna ,Directional antenna ,business.industry ,Frequency band ,MIMO ,Bandwidth (signal processing) ,Smart antenna ,Impedance matching ,Electrical Engineering, Electronic Engineering, Information Engineering ,law.invention ,law ,Electronic engineering ,Electrical and Electronic Engineering ,business - 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 multiple-input-multiple-output (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 (818-896 MHz, 1841-2067 MHz), dual-antenna prototype was designed on a 130 × 66-mm2 chassis for Long Term Evolution (LTE) operation. Full-wave simulation results were experimentally verified with a fabricated prototype.
- Published
- 2013
17. Design of multi-antenna feeding for MIMO terminals based on characteristic modes
- Author
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Buon Kiong Lau, Zachary Miers, and Hui Li
- Subjects
Coupling ,Engineering ,Chassis ,business.industry ,Quantitative Biology::Molecular Networks ,Capacitive sensing ,MIMO ,Electrical engineering ,Near and far field ,Electrical Engineering, Electronic Engineering, Information Engineering ,Terminal (electronics) ,Radiator (engine cooling) ,Antenna (radio) ,business - 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.
- Published
- 2013
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