| 1. |
- Ahlberg, M., et al.
(author)
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Downlink propagation measurements in the GSM 900 and 1800 MHz bands
- 1999
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In: IEEE Antennas and Propagation Society International Symposium. 1999 Digest. Held in conjunction with: USNC/URSI National Radio Science Meeting (Cat. No.99CH37010). ; , s. 1506-1509 vol.3
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Conference paper (peer-reviewed)abstract
- The authors investigate radio propagation in the GSM 900 and 1800 MHz bands in a typical Swedish suburban environment to determine whether or not it is practically feasible to co-site GSM 900 with GSM 1800 systems. They show that propagation in the GSM 1800 band is considerable higher (about 12 dB) than in the old GSM 900. In many cases this difference can be reduced by using dual band sector antennas with 3 dB higher gain at 1800 MHz. However, they also show that in small cells (radius <1000 m) this difference is of little concern and therefore it is possible to co-locate GSM 1800 sites within existing 900 MHz sites as a cost-effective way to increase the system capacity.
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| 2. |
- Beckman, Claes, 1962-, et al.
(author)
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Antenna diversity for mobile telephones
- 1998
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In: <em>IEEE Antennas and Propagation Society International Symposium. 1998 Digest. Antennas: Gateways to the Global Network. Held in conjunction with: USNC/URSI National Radio Science Meeting (Cat. No.98CH36</em>, Atlanta, GA, 1998, pp. 2220-2223 vol.4.. ; , s. 2220-2223
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Conference paper (peer-reviewed)abstract
- There have been several studies made on new diversity antennas for the mobile telephones. The main idea has been to have a built-in (planar) antenna working together with the conventional external. The purpose of this paper is to examine the concept of diversity further and to design two different concepts, one with two external antennas and one with an external antenna combined with an in-built. For evaluation a MATLAB program developed by the Center for Personkommunikation, CPK, in Aalborg, Denmark, is used. Given the radiation pattern from each antenna and the incoming field distribution from the environment, this program calculates the diversity performance of the system assuming that selection combining is used to combine the signals
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| 3. |
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| 4. |
- Beckman, Claes, 1962-
(author)
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Antenna-to-Antenna Isolation Measurements
- 1999
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Reports (other academic/artistic)abstract
- In this document we show results from measurements of the antenna-to-antenna isolation between different types of base station antenna configurations. The measurements are conducted on antennas for the GSM1800 band. However, since this band is relatively close to the IMT-2000 band it is reasonable to assume similar results for antennas to be used in this band.In this report we present measurement results from antennas with both vertical and slanted dual polarisation, and different horizontal beamwidths. The different antennas are shown in Table 1. The isolation is measured with the antennas positioned for some different configurations.
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| 5. |
- Beckman, Claes, 1962-, et al.
(author)
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Confocal fundus imaging with a scanning laser ophthalmoscope in eyes with cataract.
- 1995
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In: British Journal of Ophthalmology. - : BMJ. - 0007-1161 .- 1468-2079. ; 79:10, s. 900-4
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Journal article (peer-reviewed)abstract
- AIMS/BACKGROUND: The study aimed to determine the influence of increased intraocular light scatter on the contrast in scanning laser ophthalmoscope (SLO) images and to examine to what extent SLO images can visualise the fundus through media opacities due to cataract.METHODS: Intraocular light scatter was estimated from measurements of letter contrast sensitivity before and after cataract surgery in five eyes. SLO images were obtained before and after surgery using confocal apertures of 1, 2, 4, and 10 mm, at laser wavelengths of 633 and 780 nm. Visibility of the fundus was determined by measurements of retinal contrast. SLO images were compared with standard fundus photographs.RESULTS: SLO images obtained before surgery revealed details of the retina that were unresolvable in the fundus photographs because of light scattering. By using one of the three smallest apertures, image contrast was further improved. However, no simple relations between aperture size, estimated light scatter, and image contrast could be found.CONCLUSION: SLO imaging was found to be superior to fundus photography for viewing the retina in eyes with cataract. Owing to the inhomogeneous nature of cataracts, the optimal choice of confocal aperture and laser wavelength is not simple and must be individualised.
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| 6. |
- Beckman, Claes, 1962-, et al.
(author)
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Dual Band Base Station Antenna Systems
- 1998
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In: Broad Band Radio Access. - Linköping. - 9163072254 ; , s. 69-74
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Conference paper (other academic/artistic)abstract
- An analysis of the possibilities of using dualband antennas in cellular radio is presented. Results from simultaneous measurements at 900 MHz and 1800 MHz are presented and analyzed. Based on the measured results, a dual polarized, dual band base station antenna has been designed. Such an antenna proveides the opportunity to replace a 4 antenna space diversity installation with a single antenna, thereby reducing costs and tower space.
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| 7. |
- Beckman, Claes, 1962-
(author)
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Dual polarised multibeam antenna
- 1999
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In: Electronics Letters. - : Institution of Engineering and Technology (IET). - 0013-5194 .- 1350-911X. ; 35:25, s. 2158-2160
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Journal article (peer-reviewed)abstract
- A dual polarised four-beam antenna array for the 1850-1990 MHz frequency band is presented. The polarisations are ±45° to vertical. The antenna has eight inputs corresponding to two orthogonal polarisations and four beams. The return loss and cross-polar isolation for a single Butler beam exceeds 15 and 22 dB, respectively. The radiation pattern is similar to an ideal Butler pattern and the cross-polarisation level is <-21 dB in the beams
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| 8. |
- Beckman, Claes, 1962-
(author)
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Implications of Dual Band Functionality on Base Station Antenna Development
- 1997
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In: Dual Band/Multi Band '97. - London.
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Conference paper (other academic/artistic)abstract
- The recent growth in cellular communications has rapidly created a need for more radio channels. In order to make better use of the available frequency bands new access techniques such as TDMA (Time Division Multiple Access), FDMA (Frequency DMA) and CDMA (Code DMA) have been introduced. Still, the need for new channels is strong and new frequency bands have therefore been allocated for wireless communication systems.These new communication systems, e.g. the European Personal Communication Network (PCN: 1710-1880MHz) and the North American Personal Communication System (PCS: 1850-1990MHz), use frequencies about twice as high as their predecessors (e.g. AMPS: 824-894MHz and GSM: 880-960MHz). However, at a time when our downtown areas already are littered with antennas, operators are not keen to install more.One solution could be to replace existing GSM or AMPS antennas with dual band GSM/PCN or AMPS/PCS. This would reduce the windload of the towers, the number of feeder cables and the whole cost of tower installations. If the dual band antennas were to be dual polarized also, the four antennas today being needed for receiving the PCN and GSM bands in a sector, could actually be replaced by one only.
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| 9. |
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| 10. |
- Beckman, Claes, 1962-
(author)
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Plausibility of assuming ideal arrays for direction of arrival estimation
- 1996
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In: IEEE Antennas and Propagation Society International Symposium. 1996 Digest. ; , s. 1364-1367 vol.2
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Conference paper (peer-reviewed)abstract
- In order to fulfil the increasing demands on capacity and coverage of mobile communication systems smart or intelligent antennas have been suggested. These antennas increase the spectral efficiency of a wireless system by using arrays of antenna elements to shape RF signals in particular directions. Generally, smart antennas can be divided into two approaches: switched multi-beam and adaptive. Adaptive antennas utilize sophisticated signal processing algorithms to continuously distinguish between the desired signal, multipath and interfering signal as well as to calculate their direction of arrival (DOA). This makes it possible to smoothly track users with main lobes and interferers with nulls and thereby constantly maximizing the SINR (signal-to-interference and noise ratio). The DOA is one of the most important parameter for an adaptive antenna system to estimate. It is also the main subject of this paper. We establish whether or not it is plausible to assume the array to be ideal (which is often assumed in array signal processing theory) when the received signals are actually collected with a physical array consisting of standard folded dipoles. In doing so we first measured the element patterns (or steering vectors) of a twelve element antenna array. The results were then used in array signal processing simulations. The performance of two DOA estimation algorithms, MUSIC and ESPRIT, are studied and compared.
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