| 1. |
- He, Sailing, et al.
(author)
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Patch Antennas Based On a Pair of DPS and SNG Metamaterial
- 2010
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In: EuCAP 2010 - The 4th European Conference on Antennas and Propagation. - 9788476534724
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Conference paper (other academic/artistic)abstract
- In this talk we show some potential applications of a pair of conventional double positive (DPS) and single negative (SNG) metamaterial blocks for specific patch antennas. We propose two designs. One is a 900- and 1800-MHz dual-band rectangular patch antenna filled with a pair of juxtaposed DPS and mu-negative (MNG) metamaterial blocks. With proper constitutive parameters and filling ratio of the material blocks, the conventional TM(020) mode is modified and broadside radiation pattern can be simultaneously achieved at both bands. The other is a two-layered rectangular patch antenna, with a bilayer of DPS and epsilon-negative (ENG) metamaterial as its substrate. Due to the super-slow TM surface wave mode that the bi-layer structure supports, the size of the patch antenna is substantially reduced as compared to conventional lambda/2 patch antennas.
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| 2. |
- Li, Hui, et al.
(author)
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A compact reconfigurable antenna with pattern diversity
- 2012
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In: Antennas and Propagation Society International Symposium (APSURSI), 2012 IEEE. - : IEEE. - 9781467304627 ; , s. 6348776-
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Conference paper (peer-reviewed)abstract
- A compact pattern reconfigurable antenna is proposed, in which the beam pattern can be switched between a monopole like radiation and a broadside radiation. Two layers and three PIN diodes are employed in the antenna. A single coaxial feed is utilized to excite both monopole mode and PIFA mode at a center frequency of 2.62 GHz. The total efficiencies of the antenna are 72% and 95% for monopole and PIFA modes, respectively. The envelope correlation coefficient calculated from the two patterns is 0.28, indicating good diversity performance of the antenna in wireless communications.
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| 3. |
- Li, Hui, et al.
(author)
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A Simple Compact Reconfigurable Slot Antenna With a Very Wide Tuning Range
- 2010
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In: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 58:11, s. 3725-3728
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Journal article (peer-reviewed)abstract
- A simple and compact slot antenna with a very wide tuning range is proposed. A 25 mm (roughly equal to lambda(H)/8, where lambda(H) corresponds to the highest frequency of the tuning range) open slot is etched at the edge of the ground. To achieve the tunability, only two lumped elements, namely, a PIN diode and a varactor diode are used in the structure. By switching the PIN diode placed at the open end of the slot, the slot antenna can resonate as a standard slot (when the switch is on) or a half slot (when the switch is off). Continuous tuning over a wide frequency range in those two modes can be achieved by adjusting the reverse bias (giving different capacitances) of the varactor diode loaded in the slot. Through optimal design, the tuning bands of the two modes are stitched together to form a very wide tuning range. The fabricated prototype has a tuning frequency range from 0.42 GHz to 1.48 GHz with S11 better than -10 dB, giving a frequency ratio (f(R) = f(u)/f(L)) of 3.52:1. The measured full spherical radiation patterns show consistent radiation characteristics of the proposed antenna within the whole tuning range.
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| 4. |
- Li, Hui, et al.
(author)
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An efficient co-located MIMO antenna for compact terminals
- 2012
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Conference paper (other academic/artistic)abstract
- The limited volume of mobile handset and the phenomenon of chassis excitation complicate the design of multiple antennas for MIMO applications. In this work, a compact co-located dual-antenna system implemented on one edge of a 100 mm by 40 mm chassis is proposed for operation below 1 GHz. The dual-antenna structure includes a folded monopole to excite the fundamental electric dipole mode of the chassis and a coupled loop working at its own fundamental magnetic dipole mode. In this way, angle and polarization diversities are achieved. In order to overcome the coupling induced by the close proximity between the feed lines of the two antennas, the phase of the feed current on the folded monopole can be optimized to achieve an isolation of above 20 dB. The phase optimization approach can also be applied to other multi-antenna systems that has similar coupling problem from the proximity of feeds. Moreover, to compensate for the narrowband property, the loop antenna can be made tunable to cover a large bandwidth. Good MIMO performance, in terms of capacity and multiplexing efficiency, is attained with the proposed antenna system. The co-located dual antenna prototype was fabricated and its performance was verified in measurements.
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| 5. |
- Li, Hui, et al.
(author)
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An efficient method of calculating signal correlation in lossy dipole arrays based on equivalent circuits
- 2013
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Conference paper (other academic/artistic)abstract
- Correlation coefficient, as a critical performance metric of multiple antenna systems, can be calculated from the 3D radiation patterns of the antennas for multipath environments with uniform 3D angular power spectrum. A simpler, faster and lower cost approach uses the antennas’ scattering parameters to determine correlation coefficient. However, the method assumes lossless antennas, and hence only achieves good accuracy for antennas with high radiation efficiencies. In this work, a method for calculating correlation coefficients in lossy dipole arrays is proposed, using only the scattering parameters and radiation efficiencies. The method is based on the equivalent circuit of antennas, and it gives a significantly better estimate of the correlation coefficient than the existing methods. The proposed method is not limited by the number of antenna elements, which is demonstrated by applying it to a four-element dipole array.
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| 6. |
- Li, Hui, et al.
(author)
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Angle and polarization diversity in compact dual-antenna terminals with chassis excitation
- 2011
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In: URSI Gen. Assem. Sci. Symp., URSIGASS. - 9781424451173 - 9781424460519
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Conference paper (peer-reviewed)abstract
- For multiple antennas on a compact terminal chassis, chassis current excitation can severely increase mutual coupling between the antennas. This is because the same characteristic mode of the chassis may be strongly excited by more than one antenna. Here, we propose to use one antenna that exploits chassis excitation and introduce a second antenna that minimizes chassis excitation. In this way, angle and polarization diversity can be realized. The concept is illustrated and verified through the design of a practical dual-antenna prototype at 920 MHz, which achieves an isolation of over 30 dB and total efficiencies of above 80%.
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| 7. |
- Li, Hui, et al.
(author)
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Calculating signal correlation in lossy dipole arrays using scattering parameters and efficiencies
- 2013
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In: 2013 7th European Conference on Antennas and Propagation, EuCAP 2013. - : EurAAP. - 2164-3342. - 9788890701832 - 9781467321877 ; , s. 519-523
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Conference paper (peer-reviewed)abstract
- Correlation coefficient, as a critical performance metric of multiple antenna systems, can be calculated from the 3D radiation patterns of the antennas for multipath environments with uniform 3D angular power spectrum. A simpler, faster and lower cost approach uses the antennas' scattering parameters to determine correlation coefficient. However, the method assumes lossless antennas, and hence only achieves good accuracy for antennas with high radiation efficiencies. In this work, a method for calculating correlation coefficients in lossy dipole arrays is proposed, using only the scattering parameters and radiation efficiencies. The method is based on the equivalent circuit of antennas, and it gives a significantly better estimate of the correlation coefficient than the existing methods. The proposed method is also applied to two folded monopole antennas in a compact terminal to demonstrate its effectiveness.
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| 8. |
- Li, Hui, et al.
(author)
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Characteristic Mode Based Tradeoff Analysis of Antenna-Chassis Interactions for Multiple Antenna Terminals
- 2012
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In: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 60:2, s. 490-502
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Journal article (peer-reviewed)abstract
- The design of multiple antennas in compact mobile terminals is a significant challenge, due to both practical and fundamental design tradeoffs. In this paper, fundamental antenna design tradeoffs of multiple antenna terminals are presented in the framework of characteristic mode analysis. In particular, interactions between the antenna elements and the characteristic modes and their impact on design tradeoffs are investigated in both theory and simulations. The results reveal that the characteristic modes play an important role in determining the optimal placement of antennas for low mutual coupling. Moreover, the ability of antenna elements to localize the excitation currents on the chassis can significantly influence the final performance. To demonstrate the effectiveness of the proposed approach, a dual-band, dual-antenna terminal is designed to provide an isolation of over 10 dB for the 900 MHz band without additional matching or decoupling structures. A tradeoff analysis of bandwidth, efficiency, effective diversity gain and capacity is performed over different antenna locations. Finally, three fabricated prototypes verify the simulation results for representative cases.
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| 9. |
- Li, Hui, et al.
(author)
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Compact and low profile co-located MIMO antenna structure with polarisation diversity and high port isolation
- 2010
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In: Electronics Letters. - : Institution of Engineering and Technology (IET). - 0013-5194 .- 1350-911X. ; 46:2, s. 108-109
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Journal article (peer-reviewed)abstract
- A compact co-located MIMO structure with high port isolation is proposed for 2.4 GHz WLAN application. The antenna structure consists of a proximity-coupled square ring patch antenna, and a probe fed planar inverted F antenna co-located inside. The operating frequency of the two radiators is designed to be at the same frequency, and a high port isolation below -25 dB is achieved with an extremely narrow edge to edge inter-antenna space of 1 mm (0.008 lambda). The total lateral size of the co-located radiators is only 0.28 lambda x 0.28 lambda, i.e. only about 25% of the size of a half-wavelength dual-port patch antenna. The MIMO structure gives high gains (> 4.0 dB), low correlation (< 0.2), and high diversity gain (about 10 dB).
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| 10. |
- Li, Hui
(author)
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Decoupling and Evaluation of Multiple Antenna Systems in Compact MIMO Terminals
- 2012
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Doctoral thesis (other academic/artistic)abstract
- Research on multiple antenna systems has been a hot topic in recent years due to the demands for higher transmission rate and more reliable link in rich scattering environment in wireless communications. Using multiple antennas at both the transmitter side and the receiver side increases the channel capacity without additional frequency spectrum and transmitted power. However, due to the limited space at the size-limited terminal devices, the most critical problem in designing multiple antennas is the severe mutual coupling among them. The aim of this thesis is to provide compact, decoupled and efficient multiple antenna designs for terminal devices. At the same time, we propose a simple and cost effective method in multiple antenna measurement. All these efforts contribute to the development of terminal devices for the fourth generation wireless communication. The background and theory of multiple antenna systems are introduced first, in which three operating schemes of multiple antenna systems are discussed. Critical factors influencing the performance of multiple antenna systems are also analyzed in details. To design efficient multiple antenna systems in compact terminals, several decoupling methods, including defected ground plane, current localization, orthogonal polarization and decoupling networks, are proposed. The working mechanism and design procedure of each method are introduced, and their effectiveness is compared. Those methods can be applied to most of the terminal antennas, reducing the mutual coupling by at least 6dB. In some special cases, especially for low frequency bands below 1GHz, the chassis of the device itself radiates like an antenna, which complicates the antenna decoupling. Thus, we extend the general decoupling methods to the cases when the chassis is excited. Based on the characteristic mode analysis, three different solutions are provided, i.e., optimizing antenna locations, localizing antenna currents and creating orthogonal modes. These methods are applied to mobile phones, providing a more reliable link and a higher transmission rate, which are evaluated by diversity gain and channel capacity, respectively. In order to measure the performance of multiple antenna systems, it is necessary to obtain the correlation coefficients. However, the traditional measurement technique, which requires the phase and polarization information of the radiation patterns, is very expensive and time consuming. In this thesis, a more practical and convenient method is proposed. Fairly good accuracy is achieved when it is applied to various kinds of antennas. To design a compact and efficient multiple antenna system, besides the reduction of mutual coupling, the performance of each single antenna is also important. The techniques for antenna reconfiguration are demonstrated. Frequency and pattern reconfigurable antennas are constructed, providing more flexibility to multiple antenna systems.
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