| 1. |
- Bach Andersen, Jørgen, et al.
(författare)
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Compact multiple antennas in a random world
- 2007
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Ingår i: International Workshop on Antenna Technology: Small and Smart Antennas Metamaterials and Applications, 2007. IWAT '07. - 1424410886
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Konferensbidrag (refereegranskat)abstract
- Recent work on compact multiple antennas in a random environment is reviewed, including extensions of the energy density antenna and the MIMO cube. The performance of handsets with multiple antennas is dependent on many factors due to the close proximity of the antennas. The distribution of scatterers in the environment has an impact on the distributed directivity of the antennas, the powers absorbed in the loads, and the correlation between the open-circuit signals. Matching the antennas is non-trivial, since the matching changes the output correlations and the efficiency. The antennas may be matched for maximum MIMO capacity for a given environment. Basic bandwidth limitations will also be discussed.
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| 2. |
- Bach Andersen, Jørgen, et al.
(författare)
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On closely coupled dipoles in a random field
- 2006
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Ingår i: IEEE Antennas and Wireless Propagation Letters. - 1548-5757. ; 5:1, s. 73-75
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Tidskriftsartikel (refereegranskat)abstract
- Reception of partially correlated fields by two closely coupled electrical dipoles is discussed as a function of load impedances and open-circuit correlations. Two local maxima of the power may be achieved for two different load impedances, but in those cases the output correlations are high. Choosing the loads to give zero output correlations is possible for almost any real-valued open-circuit correlation with a resulting reduction of received power or gain. However, the excess loss is only of the order 1.5 $ dB$ for a spacing as small as 0.05 wavelength.
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| 3. |
- Fei, Yuanyuan, et al.
(författare)
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Experiments of closely coupled monopoles with load matching in a random field
- 2006
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Ingår i: First European Conference on Antennas and Propagation EuCAP, 2006. - 9789290929376
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Konferensbidrag (refereegranskat)abstract
- Recent theoretical and simulation studies reveal that closely coupled antennas with appropriately chosen impedance matching loads can yield desired characteristics of small antenna correlation coefficients and/or high received power levels. However, no experiment has been performed to verify these claims. Here, we describe an experimental setup used to investigate the correlation and received power of closely coupled antennas with impedance matching. Specifically, a two-monopole array with a small antenna spacing 0.05 wavelength and five different matching networks are constructed and measured. Whereas our experimental results largely confirm theoretical predictions, some discrepancies due to simplifications made in the theoretical models are observed.
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| 4. |
- Hansson Mild, Kjell, 1942-, et al.
(författare)
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Is there any exposure from a mobile phone in stand-by mode?
- 2012
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Ingår i: Electromagnetic Biology and Medicine. - : Informa Healthcare. - 1536-8378 .- 1536-8386. ; 31:1, s. 52-56
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Tidskriftsartikel (refereegranskat)abstract
- Several studies have been using a GSM mobile phone in stand-by mode as the source for exposure, and they claimed that this caused effects on for instance sleep and testicular function. In stand-by mode the phone is only active in periodic location updates, and this occurs with a frequency set by the net operator. Typical updates occur with 2-5 h in between, and between these updates the phone is to be considered as a passive radio receiver with no microwave emission. Thus, the exposure in stand-by mode can be considered negligible.
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| 5. |
- Lau, Buon Kiong
(creator_code:cre_t)
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An antenna system and a method for operating an antenna system
- 2011
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Patent (övrigt vetenskapligt/konstnärligt)abstract
- An antenna system is disclosed that includes two or more antennas and an impedance matching network. The antennas of the antenna system are closely separated, such as by a distance of no more than a wavelength of received signals divided by two. The impedance matching network is adapted to respond to and counteract performance degradation resulting from cross coupling between the antennas. Related methods for use in an antenna system are disclosed.
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| 6. |
- Lau, Buon Kiong, et al.
(författare)
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Antenna matching for capacity maximization in compact MIMO systems
- 2006
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Ingår i: 3rd International Symposium on Wireless Communication Systems, ISWCS '06. - 9781424403974 ; , s. 253-257
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Konferensbidrag (refereegranskat)abstract
- As MIMO technology slowly matures, it is finding its way into more wireless applications. However, some important applications, including mobile communications, require compact implementations. One important challenge in miniaturizing MIMO systems for compact terminals is to overcome capacity performance degradation resulting from mutual coupling among closely separated antennas. In this contribution, we begin with a review of the state-of-the-art, with particular emphasis on impedance matching and its impact on capacity. Whereas it has been shown that a multiport extension of the conjugate match is optimum in a reference environment with uniform 3D angular power spectrum, its bandwidth is severely reduced by decreasing antenna separation. On the other hand, noncoupled, individual port matching is inherently simpler to implement and broader in bandwidth, but offers a smaller capacity. Here, we demonstrate that mean capacity can be easily maximized with respect to individual port matching in a given random field. The extent of capacity gains provided by the optimized matching network over existing individual port matching networks strongly depends on the propagation environment.
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| 7. |
- Lau, Buon Kiong, et al.
(författare)
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Direction-of-arrival estimation for closely coupled arrays with impedance matching
- 2007
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Ingår i: 6th International Conference on Information, Communications & Signal Processing, 2007. - 9781424409822 ; , s. 1015-1019
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Konferensbidrag (refereegranskat)abstract
- Conventionally, the spacing between adjacent elements in an antenna array are set at half-a-wavelength in order to obtain maximum spatial resolution while avoiding spurious sidelobes. However, for antenna arrays that are implemented in a compact manner, the spacing between the adjacent elements can be significantly less than half-a- wavelength. The small spacing between the antennas results in strong mutual coupling between the antennas, which has been shown to affect the performance of array algorithms, through modifying the antenna pattern and reducing the antenna efficiency. Recently, impedance matching techniques have been proposed for multiple antenna systems for diversity and MIMO applications, in order to counteract the aforesaid coupling effects. In this paper, we study the impact of different impedance matching conditions on the Cramer-Rao bound performance of direction-of-arrival estimation using closely coupled arrays. We demonstrate that an appropriate matching network can drastically improve the CRB performance with respect to 50 ohm termination or self impedance termination with coupling, and the case of ideal antenna arrays with no coupling. For example, a tenfold reduction in RMSE over the simple matching terminations was obtained with the multiport conjugate match for a two signal scenario and an antenna separation of 0.1 wavelength.
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| 8. |
- Lau, Buon Kiong, et al.
(författare)
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Impact of impedance matching on direction-of-arrival estimation of compact antenna arrays
- 2007
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Conventionally, the spacing between adjacent elements in an antenna array are set at half-a-wavelength in order to obtain maximum spatial resolution while avoiding spurious sidelobes. However, for antenna arrays that are implemented in a compact manner, the spacing between the adjacent elements can be significantly less than half-a-wavelength. The small spacing between the antennas results in strong mutual coupling between the antennas, which has been shown to affect the performance of array algorithms, through modifying the antenna pattern and reducing the antenna efficiency. Recently, impedance matching techniques have been proposed for multiple antenna systems for diversity and MIMO applications, in order to counteract the aforesaid coupling effects. In this paper, we study the impact of different impedance matching conditions on the Cramer-Rao bound performance of direction-of-arrival estimation of compact antenna arrays. We demonstrate that an appropriate matching network can drastically improve the CRB performance with respect to both 50 ohm termination and the case of ideal antenna arrays with no coupling. For example, a ten-fold reduction in RMSE was obtained with the multiport conjugate match for a two signal scenario and an antenna separation of 0.1*wavelength.
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| 9. |
- Lau, Buon Kiong, et al.
(författare)
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Impact of matching network on bandwidth of compact antenna arrays
- 2006
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 54:11, s. 3225-3238
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Tidskriftsartikel (refereegranskat)abstract
- We analyze the impact of the matching network on compact multiple-input multiple-output systems. Existing studies have found that the matching network has a significant influence on the performance of multiple antenna systems when the antennas are in close proximity. However, none has examined the wide-band case. In this paper, we investigate the wide-band performance of four different matching networks for multiple dipole antennas. The performance of the matching networks is given in terms of the bandwidths of correlation and matching efficiency, which are extensions of the single-antenna concept of bandwidth to multiple antenna systems. We also investigate the impact of the propagation conditions on the matching and bandwidth. For a uniform two-dimensional (2-D) angular power spectrum, we find that while individual-port matching can achieve in excess of 3% fractional correlation bandwidth for envelope correlation of 0.5 at an antenna separation of 0.01 lambda, multiport matching is required for efficiency bandwidth to exist for a return loss of -6 dB. Moreover, even with multiport matching, both correlation and efficiency bandwidths decrease drastically at small antenna separations. At 0.01 lambda, the correlation and efficiency bandwidths are 0.4% and 0.2%, respectively. Similar evaluations were performed for measured outdoor-to-indoor channels with moderate to small 2-D angular spreads. We find that the efficiency advantage of multiport matching over individual-port matching diminishes with decreasing angular spread.
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| 10. |
- Lau, Buon Kiong, et al.
(författare)
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Impact of matching network on the capacity of compact MIMO systems
- 2006
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Ingår i: Antenn 06 - The Nordic Antenna Symposium.
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Konferensbidrag (refereegranskat)abstract
- MIMO is an undisputed breakthrough in advanced wireless technology, as it offers potentially linear increase in information-theoretic capacity with the number of antennas. However, the implementation of MIMO in compact terminals is a relatively uncharted topic, due to challenging problems with high antenna correlation and mismatch loss, both of which greatly reduces the expected MIMO gains. In this paper, we investigate the remedial impact of matching networks on the capacity degradation in such systems with respect to both uniform 2D angular power spectrum and measured wideband outdoor-toindoor channels. We find that the optimum narrowband multiport-matching network can perform poorly in the wideband case. For a modest 2.3% fractional bandwidth, the narrowband and wideband capacities (per unit bandwidth) can differ by as much as 60%. The multipath richness of the propagation scenario is also shown to have an important effect on the benefits that can be derived from more sophisticated matching networks which take into account mutual coupling in their designs.
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