| 1. |
- Azremi, Abdullah Al-Hadi, et al.
(författare)
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Design and Measurement-Based Evaluation of Multi-Antenna Mobile Terminals for LTE 3500 MHz Band
- 2013
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Ingår i: Progress in Electromagnetics Research B. - 1937-6472. ; 53:53, s. 241-266
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Tidskriftsartikel (refereegranskat)abstract
- Design of multi-element antennas for small mobile terminals operating at higher frequencies remains challenging despite smaller antenna dimension and possibility of achieving electrically large separation between them. In this paper, the importance of the type of radiating elements operating at 3400-3600 MHz and their locations on the terminal chassis are highlighted. An isotropic radiation pattern that receives incoming signals from arbitrary directions is obtained by combining the radiation patterns of multiple antennas with localized chassis current distribution. Four multiport antennas configurations with two- and eight-element antennas are designed and evaluated experimentally in indoor propagation environments. Our proposed designs of multi-element antennas provide the highest MIMO channel capacity compared to their counterparts using antennas with less localized chassis current distribution, even in the presence of user's hand.
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| 2. |
- Azremi, A.A.H., et al.
(författare)
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On diversity performance of two-element coupling element based antenna structure for mobile terminal
- 2010
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Ingår i: EuCAP 2010 Fourth European Conference on Antennas and Propagation, Barcelona, 12-16 April 2010.
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Konferensbidrag (refereegranskat)abstract
- In wireless communication systems, multipath interference has a significant impact on system design and performance. Fast fading is caused by the coherent summation of one or more echoes from many reflection points reaching the receive antenna. Antenna diversity can be used to mitigate multipath fading. The main challenge of antenna diversity in practical application is the integration of multiple antennas on a small ground plane. Two-element antenna structure based on coupling element antenna concept for diversity application has been studied in previous work and it has shown to be feasible for low frequency diversity application with stable and low envelope correlation across wide frequency range. The studied structure has been tuned to be operating at 1600 MHz for measurement evaluation purpose. This paper presents an analysis of diversity performance of the structure in terms of efficiencies, envelope correlation, and apparent and effective diversity gains in isotropic (i.e. statistically uniform) propagation channel, using spherical near-field technique in an ideal line-of-sight environment (anechoic chamber) and inside reverberation chamber. The envelope correlation is less than 0.1 and the diversity gain is equal to 10.2 dB at 99% reliability level using selection combining technique across simulation and both measurement methods. The measurement techniques are compared to show how accurately the diversity performance of a mobile terminal antenna can be estimated.
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| 3. |
- Gomez-Calero, C., et al.
(författare)
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Comparison of different MIMO antenna arrays and user's effect on their performances
- 2013
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Ingår i: Microwave and Optical Technology Letters. - : Wiley. - 1098-2760 .- 0895-2477. ; 55:9, s. 2039-2043
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Tidskriftsartikel (refereegranskat)abstract
- Multiple-input multiple-output (MIMO) systems have entailed a great enhancement in wireless communications performances. The use of multiple antennas at each side of the radio link has been included in recent drafts and standards such as WLAN, WIMAX, or DVB-T2. The MIMO performances depend on the antenna array characteristics and thus several aspects have to be taken into account to design MIMO antennas. In the literature, many articles can be found in terms of capacity or antenna design, but in this article, different types of antenna arrays for MIMO systems are measured in a reverberation chamber with and without a phantom as a users head. As a result, the MIMO performances are degraded by the user in terms of efficiency, diversity gain, and capacity. Omnidirectional antennas such as monopoles with high radiation efficiency offer the highest performance for a rich scattering nonline of sight indoor environment.
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| 4. |
- Gómez Calero, Carlos, 1981, et al.
(författare)
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Effect of Mutual Coupling and Human Body on MIMO Performances
- 2009
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Ingår i: 2009 Proceedings of the Third European Conference on Antenna and Propagation, EuCAP. - 9783000245732 ; , s. 1042-1046
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Konferensbidrag (refereegranskat)abstract
- In the last recent years, MIMO (Multiple Input and Multiple Output) system have been studied and developed by many researchers. These systems allow an increase in the binary data rate and the improvement of the quality of received signals, due to spatial multiplexing and space-time diversity. The performances of MIMO systems depend on the antenna design. In this paper, we focused on the importance of mutual coupling and human effect on the MIMO performances. Three different types of antennas have been designed: monopoles, cross-polarized dipoles and a Planar Inverted-F Antennas (PIFAs). The antennas work at 2.45 GHz for WLAN applications and also PIFAs work at GSM 1800 and 5.4 GHz for the other WLAN band. The results show the importance of spacing among radiating elements due to the mutual coupling and measurements in a reverberation chamber comparing the effect of the user's head.
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| 5. |
- Jamaly, Nima, 1979, et al.
(författare)
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A Revisit to Spatial Correlation in Terms of Input Network Parameters
- 2012
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Ingår i: IEEE Antennas and Wireless Propagation Letters. - 1548-5757 .- 1536-1225. ; 11, s. 1342-1345
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Tidskriftsartikel (refereegranskat)abstract
- An alternative compact formula in terms of input network parameters for calculation of envelope correlations is provided. The main advantage of this formula is that it can be simply modified to include cases of lossy structures and general cases of correlated nonuniform multipath environments. This formula is based on the open-circuit covariance matrix of the multiport antennas. The latter can be either estimated or quickly measured in a reverberation chamber, which removes the need for costly measurements of the embedded far field patterns.
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| 6. |
- Jamaly, Nima, 1979, et al.
(författare)
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Analysis and Measurement of Multiple Antenna Systems for Fading Channel Prediction in Moving Relays
- 2014
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Ingår i: 2014 8TH EUROPEAN CONFERENCE ON ANTENNAS AND PROPAGATION (EUCAP). - 2164-3342. - 9788890701849 ; , s. 2015-2019
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The performance of wireless data transmission to mobile vehicles is improved if channel state information is available at the transmitter but movement of vehicles causes outdating of channel estimates. The concept of a predictor antenna has recently been proposed, where an antenna is placed in front of other antennas on the roof of the vehicle to sense the radio environment in advance. This can comparatively provide an order-of-magnitude improvement in channel prediction performance. A potential problem with this idea is that closely placed antennas will experience mutual electromagnetic couplings. These may reduce the efficiency of the predictor antenna concept if they are not taken into account. In this paper, we discuss about how to treat the forgoing issue and eventually evaluate a promising candidate on measured channels. We argue that only open-circuit voltage method would be realistic for the present application. The usefulness of the proposed decoupling method is demonstrated on field measurements obtained in downtown Dresden, Germany. We also partly address the sensitivity of the open-circuit decoupling method to the accuracy of the utilized network parameters.
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| 7. |
- Jamaly, Nima, 1979, et al.
(författare)
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Analysis of Antenna Pattern Overlap Matrix in Correlated Nonuniform Multipath Environments
- 2013
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Ingår i: Proceedings of the 7th European Conference on Antennas and Propagation. - 2164-3342. - 9788890701832 ; , s. 2113-2117
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Konferensbidrag (refereegranskat)abstract
- In this paper the covariance matrix of received voltage signals across ports of a multiport antenna in correlated multipath environments is formulated. This eventually leads to some expressions for mean effective gain and directivity in these environments, which to our best knowledge has not been addressed before. The notion of pattern overlap matrix is utilized to coin correlated pattern overlap matrix. We show the crucial role of the latter parameter in general correlated multipath environments.
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| 8. |
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| 9. |
- Jamaly, Nima, 1979, et al.
(författare)
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Compact Formulas for Diversity Gain of Two-Port Antennas
- 2010
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Ingår i: IEEE Antennas and Wireless Propagation Letters. - 1548-5757 .- 1536-1225. ; 9, s. 970-973
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Accuracy limitation in evaluation of diversity gains based on cumulative distribution function curves is highlighted. New devised closed-form formulas are provided for Selection Combining and Maximum Ratio Combining diversity schemes rendering diversity gain as a function of correlation and radiation efficiencies. Accuracy of these formulas is studied and verified by numerical simulations. These formulas take a central role for the cases when engineers are limited to a finite number of measured voltage samples at different ports to provide them with accurate calculation of ergodic diversity gain. This letter also reveals dependency of different diversity gains upon total embedded efficiencies of branches and underscores the significance of identical efficiencies of two-element terminals for their optimum performance in multipath environments. © 2010 IEEE.
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| 10. |
- Jamaly, Nima, 1979, et al.
(författare)
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Coupling effects on richness threshold of multi-port antennas in multipath environments
- 2012
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Ingår i: 15th International Symposium on Antenna Technology and Applied Electromagnetics, ANTEM 2012, Toulouse, 25-28 June 2012. - 9781467302906
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Konferensbidrag (refereegranskat)abstract
- This paper investigates convergence in diversity gain of multi-port antennas in non-rich multipath environments. It is shown that diversity gain convergence is faster in the presence of strong coupling. In this situation, richness threshold is also smaller. Furthermore, by linking convergence in diversity gain to convergence in antenna ports' correlations, the role of pattern diversity caused by coupling is highlighted. A range of variation for correlations is defined whose upper bound is used to quantify pattern diversity. The lower bound for this range is the corresponding spatial correlation in a rich multipath environment.
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| 11. |
- Jamaly, Nima, 1979, et al.
(författare)
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Effects of coupling and overspeeding on performance of predictor antenna systems in wireless moving relays
- 2019
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Ingår i: IET Microwaves, Antennas and Propagation. - : Institution of Engineering and Technology (IET). - 1751-8725 .- 1751-8733. ; 13:3, s. 367-372
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Tidskriftsartikel (refereegranskat)abstract
- Using predictor antenna systems for modern wireless moving relays and base stations on top of vehicles such as buses, trains etc. proves to be a reliable approach for collecting channel state information to such fast moving nodes. Recently, it has been shown that coupling between different ports of a multiport antenna system used as a part of a predictor system can reduce the prediction performance. In this study, by integrating position and velocity vectors in the channel covariance matrix as seen at the antenna ports in a rich multipath environment, the authors quantify the impact of antenna coupling on prediction performance. Moreover, practically these predictor systems are designed for a certain target velocity. They further quantify the adverse effect of velocities, different from the target velocity, on prediction performance. In case open-circuit decoupling is necessary, the sensitivity of the predictor antenna system performance with respect to the accuracy of the input network parameters is disclosed.
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| 12. |
- Jamaly, Nima, 1979, et al.
(författare)
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Efficiency characterisation of multi-port antennas
- 2012
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Ingår i: Electronics Letters. - : Institution of Engineering and Technology (IET). - 1350-911X .- 0013-5194. ; 48:4, s. 196-197
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Tidskriftsartikel (refereegranskat)abstract
- A simple radiation efficiency metric is introduced to include the effects of non-ideal source/receiver impedances. The features of this parameter are highlighted and its compact formula is derived. The notion of mean matching efficiency is established. Simulations prove that this matching efficiency is quite useful in a quick estimation of diversity performance of multi-port antennas in rich isotropic multipath environments.
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| 13. |
- Jamaly, Nima, 1979, et al.
(författare)
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Fast Measurement of Antenna Pattern Overlap Matrix in Reverberation Chamber
- 2013
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Ingår i: Electronics Letters. - : Institution of Engineering and Technology (IET). - 1350-911X .- 0013-5194. ; 49:5, s. 318-319
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Tidskriftsartikel (refereegranskat)abstract
- Presented is a fast way for the measurement of the pattern overlap matrix in an arbitrary multi-port antenna system by a reverberation chamber. This parameter is central for calculation of the spatial correlation between different elements with arbitrary terminations. To the authors' knowledge, this is the fastest method for the measurement of the pattern overlap matrix in a lossy structure.
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| 14. |
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| 15. |
- Jamaly, Nima, 1979, et al.
(författare)
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Multi-port matching efficiency in antenna systems with cascaded networks
- 2012
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Ingår i: 15th International Symposium on Antenna Technology and Applied Electromagnetics, ANTEM 2012, Toulouse, 25-28 June 2012. - 9781467302906
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Konferensbidrag (refereegranskat)abstract
- A general compact formula for multi-port matching efficiency in the presence of an arbitrary number of cascaded networks is introduced. A comparison between the decoupling efficiency and multi-port matching efficiency is presented. Similarly, a compact formula for decoupling efficiency in a cascaded chain is provided. The presented compact formulas are quite advantageous for optimization of radiation efficiencies by designing a proper matching network.
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| 16. |
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| 17. |
- Jamaly, Nima, 1979
(författare)
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Multiport Antenna Systems for Space-Time Wireless Communications
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Multiport antenna systems are indispensable part of modern wireless communication systems. Their crucial impact on the overall performance requires sufficient regard and dedication to a precise design and characterisation. This concern has been to a considerable extent addressed in the frame of the current thesis. The thesis starts by a brief review of the evolution on wireless communication systems. In particular, the role of multiport antennas in modern communication systems is highlighted. The multidisciplinary nature of multiport radiation terminals makes them the subject of many research groups worldwide, resulting in inconsistent nomenclature. Thus, a few words are dedicated to throwing light upon some important metrics in this discipline. The notion of richness threshold as a further crucial performance metric is introduced. The importance of the latter parameter is emphasised by virtue of some practical examples. We describe how an RF Butler network can be used to remarkably enhance the performance of spatial diversity systems. Subsequently, the advantage of a predictor antenna system in modern moving relays is underlined. We illustrate and quantify how the coupling removal can improve the prediction capability of this system. This can be most conveniently carried out through signal processing, amplifying the prediction reliability. To verify the foregoing achievement, some results associated with measurements in actual scenarios are presented. Moreover, a quick and inexpensive measurement of antennas in multipath environments is of foremost concern for antenna system designers. This issue is simply possible by reverberation chamber technologies. We briefly clarify how further analysis can be utilised to facilitate measurements in these chambers. At the end, we devote a short discussion to some state-of-the-art antenna designs which are suitable for the modern compact mobile terminals, manifesting certain rewarding features.
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| 18. |
- Jamaly, Nima, 1979, et al.
(författare)
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Performance evaluation of diversity antennas in multipath environments of finite richness
- 2012
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Ingår i: Proceedings of 6th European Conference on Antennas and Propagation, EuCAP 2012. Prague, 26-30 March 2012. - 9781457709180 ; , s. 368-372
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Konferensbidrag (refereegranskat)abstract
- The simulation tool introduced in [1] is extended further to include the emulation of non-uniform multipath environments. This extension creates a trend to generalize the definition of effective diversity gain to be applicable to non-uniform multipath environments too. We introduce the richness threshold as a further metric for diversity performance of multi-port antennas. By virtue of this novel parameter, we demonstrate that beam-forming, which is ineffective in a rich isotropic multipath environment, is beneficial in non-rich isotropic multipath environments.
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| 19. |
- Jamaly, Nima, 1979, et al.
(författare)
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Performance of directive multi-element antennas versus multi-beam arrays in MIMO communication systems
- 2010
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Ingår i: EuCAP 2010 Fourth European Conference on Antennas and Propagation, Barcelona, 12-16 April 2010. - 9781424464319
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Konferensbidrag (refereegranskat)abstract
- In an isotropic rich scattering environment, the shape of the patterns of the elements has long been considered as irrelevant to their Multiple-Input and Multiple-Output (MIMO) performances. In the current communication it is cleared that the directivities of the embedded elements, which are immediate outcomes of their patterns, contribute to the diversity gains as well as capacity of the system. Indeed, the number of scatterers plays a significant role in this respect. It is demonstrated that unless the number of scatterers is high enough, the diversity gain and capacity do not reach their final limits, even though the spatial correlation and radiation efficiencies reside on their ideally best levels. A brief study of the matter is presented in this paper and the simulation results are verified by measurements in reverberation chamber.
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| 20. |
- Jamaly, Nima, 1979
(författare)
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Spatial Characterization of Multi-element Antennas
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The overall goal of the current thesis is to establish some bases for understanding and characterization of multi-port antennas in a rich multipath environment. Multi-port antennas are the inevitable keystone of multiple input and multiple output wireless communication systems. Due to multidisciplinary nature of the applications of multi-element antennas, they are the subjects of many research groups worldwide resulting in inconsistent nomenclature among them. In this thesis, much effort is expended to look upon this realm of engineering in a unifying approach, with the major stress on electromagnetic aspects of this area. The thesis throws light upon different significant parameters as the key-gauges for characterization of multi-port antennas. We illustrate the dependency of precise measurement of diversity gains upon total number of independent measured samples. Two closed-form formulas are devised rendering diversity gains of two-port antennas in a rich scattering environment. Some examples are presented to verify the accuracy of these formulas. Moreover, received signals at different ports of a multi-element antenna in a multipath environment are the major sources for its assessment. There are certain functions governing the relation between the received signals at different ports of a radiation system and an arbitrary incident electromagnetic wave. The precise derivation of these formulas for different cases of interest are presented in this thesis. Furthermore, it has been frequently acknowledged that in a uniform rich multipath environment the beam-forming technique does not prove beneficial. Here for the first time, we stress that in a uniform non-rich scattering environment, beam-forming technique bestows considerable gain. We demonstrate that the achieved gain in respect to a similar radiation system reduces as the multipath environment becomes richer. In addition to that, it is known that reverberation chambers are the contemporary measurement tools for antenna systems to be used in scattering environments. The shape of these measurement tools plays a significant role in their ultimate performance. We show that rectangular reverberation chambers prove to be more advantageous compared with their cylindrical and spherical counterparts.
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| 21. |
- Jamaly, Nima, 1979, et al.
(författare)
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Spatial Diversity Performance of Multiport Antennas in the Presence of a Butler Network
- 2013
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X .- 1558-2221. ; 61:11, s. 5697-5705
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Tidskriftsartikel (refereegranskat)abstract
- The main concern of this paper is to study the presence of a cascaded Butler network in diversity antenna systems. The advantages of a cascaded Butler network in 2Dmultipath environments have been already shown. These advantages are limited to either correlated or nonuniform multipath environments with a line-of-sight component. In the frame of this paper, for the first time, we show a further advantage of a cascaded Butler network in 3D multipath environments, including the effects of coupling. This advantage is associated with an improved convergence in received signals’ covariance matrix in a multipath environment wherein the number of independent incoming waves is limited, i.e., non-rich multipath environment. For this purpose, we use a simulation tool in which a multipath scenario with certain number of incoming waves is emulated and some selected multiport antennas are exposed to it. Afterwards, the simulated random received signals are used to yield different performance metrics like spatial correlation. This advantage achieves considerable practical interest since a typical actual multipath scenario is most likely a non-rich multipath environment.
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| 22. |
- Jamaly, Nima, 1979, et al.
(författare)
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Study of Excitation on Beam Ports versus Element Ports in Performance Evaluation of Diversity and MIMO Arrays
- 2009
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Ingår i: 3rd European Conference on Antennas and Propagation, EuCAP 2009; Berlin; Germany; 23 March 2009 through 27 March 2009. - 9783000245732 ; , s. 1753-1757
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Konferensbidrag (refereegranskat)abstract
- The main concern of the current communication is to elicit the influences of beam-forming upon different Multiple- Input Multiple-Output (MIMO) parameters in a rich scattering environment. A detailed study of desired parameters is presented with particular stress on total radiation efficiencies observed on Element ports and Beam ports. Measurements are performed in a Reverberation Chamber (RC). The results illustrate that performance as viewed through Element and Beam ports are, in general, equal. Hence, they confirm that in a rich and isotropic scattering environment, beam-forming technique does not prove beneficial. They also demonstrate that as long as received radiation power is preserved, the shapes of the elements' patterns are irrelevant.
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| 23. |
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| 24. |
- Kildal, Per-Simon, 1951, et al.
(författare)
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Performance of different theoretical small antennas in isotropic 3-D and horizontal 2-D multipath environments with application to OTA testing
- 2010
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Ingår i: 2010 IEEE International Symposium on Antennas and Propagation, Toronto, July 11-17, 2010. - 1522-3965. - 9781424449682
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Konferensbidrag (refereegranskat)abstract
- We have studied the performance of antennas in inherently polarization-balanced horizontal 2-D multipath environments with angles of arrival in the horizontal plane only. The average received power may vary up to 3 dB depending on type of small antenna and its orientation, and, the observed polarization balanced may be anything between +3 and 3 dB, depending on the antenna by which it is measured.
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| 25. |
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