| 1. |
|
|
| 2. |
- Li, Hui, et al.
(författare)
-
An efficient co-located MIMO antenna for compact terminals
- 2012
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)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.
|
|
| 3. |
- Li, Hui, et al.
(författare)
-
An efficient method of calculating signal correlation in lossy dipole arrays based on equivalent circuits
- 2013
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)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.
|
|
| 4. |
- Li, Hui, et al.
(författare)
-
Analysis and estimation of MIMO-SAR for multi-antenna mobile handsets
- 2017
-
Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; , s. 1522-1527
-
Tidskriftsartikel (refereegranskat)abstract
- Measuring MIMO-SAR is an important part of mobile handset evaluation, following the introduction of uplink MIMO transmission schemes in LTE-Advanced. However, the measurement of MIMO-SAR is complex and time-consuming. In this paper, 6 unique dual-antenna mobile handsets, including both typical and novel designs, are analyzed to determine the dependence of MIMO-SAR on antenna configuration and correlation. It is found that, for certain antenna configurations, the location of the maximum MIMO-SAR and the corresponding relative phase between the ports can be predicted. This can be applied to drastically reduce measurement time. In addition, dual-antennas with low envelope correlation coefficients in the radiation patterns also offer near-orthogonal electric near-fields. This leads to smaller MIMO-SAR than stand-alone SAR (S-SAR) over all relative phases, making MIMO-SAR measurement unnecessary. The results also provide guidelines for designing multi-antenna handsets with low SARs. For verification, the S- SAR and MIMO-SAR at relative phase of 0° were measured for several handsets. The measured SAR distributions showed good agreement with the simulated ones.
|
|
| 5. |
- Li, Hui, et al.
(författare)
-
Analysis of SAR on flat phantom for different multi-antenna mobile terminals
- 2014
-
Ingår i: European Conference on Antennas and Propagation (EuCAP), 2014. - 2164-3342. - 9788890701849 ; , s. 1989-1989
-
Konferensbidrag (refereegranskat)abstract
- Evaluation of Specific Absorption Rate (SAR) for multiple antenna systems is becoming important, with the upcoming deployment of LTE-Advanced. In this work, the influence of different antenna locations and antenna types was investigated for stand-alone SAR and simultaneous SAR, to provide some guidelines for antenna design in multi-antenna handsets. For simultaneous SAR, different phase shifts between antenna ports were considered and the averaged SAR was used as a metrics for comparison. The SAR performances were evaluated in simulation for the body worn scenario, and different placements of the mobile handset, i.e., with either the screen or back side closer to the body, were studied.
|
|
| 6. |
- Li, Hui, et al.
(författare)
-
Angle and polarization diversity in compact dual-antenna terminals with chassis excitation
- 2011
-
Ingår i: URSI Gen. Assem. Sci. Symp., URSIGASS. - 9781424451173 - 9781424460519
-
Konferensbidrag (refereegranskat)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%.
|
|
| 7. |
- Li, Hui, et al.
(författare)
-
Antenna design tradeoff of multiple antenna terminals with ground plane excitation
- 2010
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- It is known that the compactness of mobile terminals complicates the design of multiple antennas, since coupling between the antennas increases when they are placed in proximity of one another. While it is possible to mitigate coupling between closely spaced antennas, a tradeoff in bandwidth is required. In this paper, we highlight ground plane excitation as an additional dimension to consider in the design of multiple antenna terminals. This is because small ground plane can interact with the antenna elements and contribute significantly to their radiation characteristics. In particular, the ground plane effect is important for mobile frequency bands lower than 1 GHz, due to the physical dimensions of today’s mobile terminals. Our results show that several design parameters, namely element locations, spacing between elements, and radiation characteristics of individual elements, must be jointly considered in order to achieve the optimum performance tradeoff for multiple antenna terminals. For example, for a two-antenna setup, even though coupling between the elements can be reduced by decreasing the element spacing to avoid ground plane excitation for one of the antennas, the bandwidth is reduced.
|
|
| 8. |
- Li, Hui, et al.
(författare)
-
Body-worn specific absorption rate for MIMO handsets with different antenna setups
- 2014
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Evaluation of Specific Absorption Rate (SAR) for multiple antenna systems is expected with the upcoming deployment of LTE Advanced, where multi-antennas are excited in both uplink and downlink. In this work, the influence of different antenna locations and antenna types was investigated for stand-alone SAR and simultaneous SAR, to provide some guidelines for antenna design in multi-antenna handsets. For simultaneous SAR, different phase shifts between antenna ports were considered and the averaged SAR was used as a metrics for comparison. The SAR performances were evaluated in the simulation for the body worn scenario (i.e., on the flat phantom), and diffe rent placements of the mobile handset, i.e., with either the screen or back side closer to the body, were studied.
|
|
| 9. |
- Li, Hui, et al.
(författare)
-
Calculating signal correlation in lossy dipole arrays using scattering parameters and efficiencies
- 2013
-
Ingår i: 2013 7th European Conference on Antennas and Propagation, EuCAP 2013. - : EurAAP. - 2164-3342. - 9788890701832 - 9781467321877 ; , s. 519-523
-
Konferensbidrag (refereegranskat)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.
|
|
| 10. |
|
|
